rfc9065.original   rfc9065.txt 
TSVWG G. Fairhurst Internet Engineering Task Force (IETF) G. Fairhurst
Internet-Draft University of Aberdeen Request for Comments: 9065 University of Aberdeen
Intended status: Informational C. Perkins Category: Informational C. Perkins
Expires: October 20, 2021 University of Glasgow ISSN: 2070-1721 University of Glasgow
April 18, 2021 June 2021
Considerations around Transport Header Confidentiality, Network Considerations around Transport Header Confidentiality, Network
Operations, and the Evolution of Internet Transport Protocols Operations, and the Evolution of Internet Transport Protocols
draft-ietf-tsvwg-transport-encrypt-21
Abstract Abstract
To protect user data and privacy, Internet transport protocols have To protect user data and privacy, Internet transport protocols have
supported payload encryption and authentication for some time. Such supported payload encryption and authentication for some time. Such
encryption and authentication is now also starting to be applied to encryption and authentication are now also starting to be applied to
the transport protocol headers. This helps avoid transport protocol the transport protocol headers. This helps avoid transport protocol
ossification by middleboxes, mitigate attacks against the transport ossification by middleboxes, mitigate attacks against the transport
protocol, and protect metadata about the communication. Current protocol, and protect metadata about the communication. Current
operational practice in some networks inspect transport header operational practice in some networks inspect transport header
information within the network, but this is no longer possible when information within the network, but this is no longer possible when
those transport headers are encrypted. those transport headers are encrypted.
This document discusses the possible impact when network traffic uses This document discusses the possible impact when network traffic uses
a protocol with an encrypted transport header. It suggests issues to a protocol with an encrypted transport header. It suggests issues to
consider when designing new transport protocols or features. consider when designing new transport protocols or features.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for informational purposes.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
This Internet-Draft will expire on October 20, 2021. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9065.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
2. Current uses of Transport Headers within the Network . . . . 4 2. Current Uses of Transport Headers within the Network
2.1. To Separate Flows in Network Devices . . . . . . . . . . 5 2.1. To Separate Flows in Network Devices
2.2. To Identify Transport Protocols and Flows . . . . . . . . 5 2.2. To Identify Transport Protocols and Flows
2.3. To Understand Transport Protocol Performance . . . . . . 6 2.3. To Understand Transport Protocol Performance
2.4. To Support Network Operations . . . . . . . . . . . . . . 13 2.4. To Support Network Operations
2.5. To Mitigate the Effects of Constrained Networks . . . . . 18 2.5. To Mitigate the Effects of Constrained Networks
2.6. To Verify SLA Compliance . . . . . . . . . . . . . . . . 19 2.6. To Verify SLA Compliance
3. Research, Development and Deployment . . . . . . . . . . . . 20 3. Research, Development, and Deployment
3.1. Independent Measurement . . . . . . . . . . . . . . . . . 20 3.1. Independent Measurement
3.2. Measurable Transport Protocols . . . . . . . . . . . . . 21 3.2. Measurable Transport Protocols
3.3. Other Sources of Information . . . . . . . . . . . . . . 22 3.3. Other Sources of Information
4. Encryption and Authentication of Transport Headers . . . . . 23 4. Encryption and Authentication of Transport Headers
5. Intentionally Exposing Transport Information to the Network . 28 5. Intentionally Exposing Transport Information to the Network
5.1. Exposing Transport Information in Extension Headers . . . 28 5.1. Exposing Transport Information in Extension Headers
5.2. Common Exposed Transport Information . . . . . . . . . . 29 5.2. Common Exposed Transport Information
5.3. Considerations for Exposing Transport Information . . . . 29 5.3. Considerations for Exposing Transport Information
6. Addition of Transport OAM Information to Network-Layer 6. Addition of Transport OAM Information to Network-Layer Headers
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.1. Use of OAM within a Maintenance Domain
6.1. Use of OAM within a Maintenance Domain . . . . . . . . . 30 6.2. Use of OAM across Multiple Maintenance Domains
6.2. Use of OAM across Multiple Maintenance Domains . . . . . 30 7. Conclusions
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 31 8. Security Considerations
8. Security Considerations . . . . . . . . . . . . . . . . . . . 34 9. IANA Considerations
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 10. Informative References
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36 Acknowledgements
11. Informative References . . . . . . . . . . . . . . . . . . . 36 Authors' Addresses
Appendix A. Revision information . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
1. Introduction 1. Introduction
The transport layer supports the end-to-end flow of data across a The transport layer supports the end-to-end flow of data across a
network path, providing features such as connection establishment, network path, providing features such as connection establishment,
reliability, framing, ordering, congestion control, flow control, reliability, framing, ordering, congestion control, flow control,
etc., as needed to support applications. One of the core functions etc., as needed to support applications. One of the core functions
of an Internet transport is to discover and adapt to the of an Internet transport is to discover and adapt to the
characteristics of the network path that is currently being used. characteristics of the network path that is currently being used.
For some years, it has been common for the transport layer payload to For some years, it has been common for the transport-layer payload to
be protected by encryption and authentication, but for the transport be protected by encryption and authentication but for the transport-
layer headers to be sent unprotected. Examples of protocols that layer headers to be sent unprotected. Examples of protocols that
behave in this manner include Transport Layer Security (TLS) over TCP behave in this manner include Transport Layer Security (TLS) over TCP
[RFC8446], Datagram TLS [RFC6347] [I-D.ietf-tls-dtls13], the Secure [RFC8446], Datagram TLS [RFC6347] [DTLS], the Secure Real-time
Real-time Transport Protocol [RFC3711], and tcpcrypt [RFC8548]. The Transport Protocol [RFC3711], and tcpcrypt [RFC8548]. The use of
use of unencrypted transport headers has led some network operators, unencrypted transport headers has led some network operators,
researchers, and others to develop tools and processes that rely on researchers, and others to develop tools and processes that rely on
observations of transport headers both in aggregate and at the flow observations of transport headers both in aggregate and at the flow
level to infer details of the network's behaviour and inform level to infer details of the network's behaviour and inform
operational practice. operational practice.
Transport protocols are now being developed that encrypt some or all Transport protocols are now being developed that encrypt some or all
of the transport headers, in addition to the transport payload data. of the transport headers, in addition to the transport payload data.
The QUIC transport protocol [I-D.ietf-quic-transport] is an example The QUIC transport protocol [RFC9000] is an example of such a
of such a protocol. Such transport header encryption makes it protocol. Such transport header encryption makes it difficult to
difficult to observe transport protocol behaviour from the vantage observe transport protocol behaviour from the vantage point of the
point of the network. This document discusses some implications of network. This document discusses some implications of transport
transport header encryption for network operators and researchers header encryption for network operators and researchers that have
that have previously observed transport headers, and highlights some previously observed transport headers, and it highlights some issues
issues to consider for transport protocol designers. to consider for transport protocol designers.
As discussed in [RFC7258], the IETF has concluded that Pervasive As discussed in [RFC7258], the IETF has concluded that Pervasive
Monitoring (PM) is a technical attack that needs to be mitigated in Monitoring (PM) is a technical attack that needs to be mitigated in
the design of IETF protocols. This document supports that the design of IETF protocols. This document supports that
conclusion. It also recognises that RFC7258 states "Making networks conclusion. It also recognises that [RFC7258] states, "Making
unmanageable to mitigate PM is not an acceptable outcome, but networks unmanageable to mitigate PM is not an acceptable outcome,
ignoring PM would go against the consensus documented here. An but ignoring PM would go against the consensus documented here. An
appropriate balance will emerge over time as real instances of this appropriate balance will emerge over time as real instances of this
tension are considered". This document is written to provide input tension are considered." This document is written to provide input
to the discussion around what is an appropriate balance, by to the discussion around what is an appropriate balance by
highlighting some implications of transport header encryption. highlighting some implications of transport header encryption.
Current uses of transport header information by network devices on Current uses of transport header information by network devices on
the Internet path are explained. These uses can be beneficial or the Internet path are explained. These uses can be beneficial or
malicious. This is written to provide input to the discussion around malicious. This is written to provide input to the discussion around
what is an appropriate balance, by highlighting some implications of what is an appropriate balance by highlighting some implications of
transport header encryption. transport header encryption.
2. Current uses of Transport Headers within the Network 2. Current Uses of Transport Headers within the Network
In response to pervasive monitoring [RFC7624] revelations and the In response to pervasive surveillance [RFC7624] revelations and the
IETF consensus that "Pervasive Monitoring is an Attack" [RFC7258], IETF consensus that "Pervasive Monitoring Is an Attack" [RFC7258],
efforts are underway to increase encryption of Internet traffic. efforts are underway to increase encryption of Internet traffic.
Applying confidentiality to transport header fields can improve Applying confidentiality to transport header fields can improve
privacy, and can help to mitigate certain attacks or manipulation of privacy and can help to mitigate certain attacks or manipulation of
packets by devices on the network path, but it can also affect packets by devices on the network path, but it can also affect
network operations and measurement [RFC8404]. network operations and measurement [RFC8404].
When considering what parts of the transport headers should be When considering what parts of the transport headers should be
encrypted to provide confidentiality, and what parts should be encrypted to provide confidentiality and what parts should be visible
visible to network devices (including non-encrypted but authenticated to network devices (including unencrypted but authenticated headers),
headers), it is necessary to consider both the impact on network it is necessary to consider both the impact on network operations and
operations and management, and the implications for ossification and management and the implications for ossification and user privacy
user privacy [Measurement]. Different parties will view the relative [Measurement]. Different parties will view the relative importance
importance of these concerns differently. For some, the benefits of of these concerns differently. For some, the benefits of encrypting
encrypting all the transport headers outweigh the impact of doing so; all the transport headers outweigh the impact of doing so; others
others might analyse the security, privacy, and ossification impacts might analyse the security, privacy, and ossification impacts and
and arrive at a different trade-off. arrive at a different trade-off.
This section reviews examples of the observation of transport layer This section reviews examples of the observation of transport-layer
headers within the network by devices on the network path, or using headers within the network by using devices on the network path or by
information exported by an on-path device. Unencrypted transport using information exported by an on-path device. Unencrypted
headers provide information that can support network operations and transport headers provide information that can support network
management, and this section notes some ways in which this has been operations and management, and this section notes some ways in which
done. Unencrypted transport header information also contributes this has been done. Unencrypted transport header information also
metadata that can be exploited for purposes unrelated to network contributes metadata that can be exploited for purposes unrelated to
transport measurement, diagnostics or troubleshooting (e.g., to block network transport measurement, diagnostics, or troubleshooting (e.g.,
or to throttle traffic from a specific content provider), and this to block or to throttle traffic from a specific content provider),
section also notes some threats relating to unencrypted transport and this section also notes some threats relating to unencrypted
headers. transport headers.
Exposed transport information also provides a source of information Exposed transport information also provides a source of information
that contributes to linked data sets, which could be exploited to that contributes to linked data sets, which could be exploited to
deduce private information, e.g., user patterns, user location, deduce private information, e.g., user patterns, user location,
tracking behaviour, etc. This might reveal information the parties tracking behaviour, etc. This might reveal information the parties
did not intend to be revealed. [RFC6973] aims to make designers, did not intend to be revealed. [RFC6973] aims to make designers,
implementers, and users of Internet protocols aware of privacy- implementers, and users of Internet protocols aware of privacy-
related design choices in IETF protocols. related design choices in IETF protocols.
This section does not consider intentional modification of transport This section does not consider intentional modification of transport
headers by middleboxes, such as devices performing Network Address headers by middleboxes, such as devices performing Network Address
Translation (NAT) or Firewalls. Translation (NAT) or firewalls.
2.1. To Separate Flows in Network Devices 2.1. To Separate Flows in Network Devices
Some network layer mechanisms separate network traffic by flow, Some network-layer mechanisms separate network traffic by flow
without resorting to identifying the type of traffic. Hash-based without resorting to identifying the type of traffic: hash-based load
load-sharing sharing across paths (e..g., equal cost multi path, sharing across paths (e.g., Equal-Cost Multipath (ECMP)); sharing
ECMP), sharing across a group of links (e.g., using a link across a group of links (e.g., using a Link Aggregation Group (LAG));
aggregation group, LAG), ensuring equal access to link capacity ensuring equal access to link capacity (e.g., Fair Queuing (FQ)); or
(e.g., fair queuing, FQ), or distributing traffic to servers (e.g., distributing traffic to servers (e.g., load balancing). To prevent
load balancing). To prevent packet reordering, forwarding engines packet reordering, forwarding engines can consistently forward the
can consistently forward the same transport flows along the same same transport flows along the same forwarding path, often achieved
forwarding path, often achieved by calculating a hash using an by calculating a hash using an n-tuple gleaned from a combination of
n-tuple gleaned from a combination of link header information through link header information through to transport header information.
to transport header information. This n-tuple can use the MAC This n-tuple can use the Media Access Control (MAC) address and IP
address, IP addresses, and can include observable transport header addresses and can include observable transport header information.
information.
When transport header information cannot be observed, there can be When transport header information cannot be observed, there can be
less information to separate flows at equipment along the path. Flow less information to separate flows at equipment along the path. Flow
separation might not be possible when, a transport that forms traffic separation might not be possible when a transport forms traffic into
into an encrypted aggregate. For IPv6, the Flow Label [RFC6437] can an encrypted aggregate. For IPv6, the Flow Label [RFC6437] can be
be used even when all transport information is encrypted, enabling used even when all transport information is encrypted, enabling Flow
Flow Label-based ECMP [RFC6438] and Load-Sharing [RFC7098]. Label-based ECMP [RFC6438] and load sharing [RFC7098].
2.2. To Identify Transport Protocols and Flows 2.2. To Identify Transport Protocols and Flows
Information in exposed transport layer headers can be used by the Information in exposed transport-layer headers can be used by the
network to identify transport protocols and flows [RFC8558]. The network to identify transport protocols and flows [RFC8558]. The
ability to identify transport protocols, flows, and sessions is a ability to identify transport protocols, flows, and sessions is a
common function performed, for example, by measurement activities, common function performed, for example, by measurement activities,
Quality of Service (QoS) classifiers, and firewalls. These functions Quality of Service (QoS) classifiers, and firewalls. These functions
can be beneficial, and performed with the consent of, and in support can be beneficial and performed with the consent of, and in support
of, the end user. Alternatively, the same mechanisms could be used of, the end user. Alternatively, the same mechanisms could be used
to support practises that might be adversarial to the end user, to support practises that might be adversarial to the end user,
including blocking, de-prioritising, and monitoring traffic without including blocking, deprioritising, and monitoring traffic without
consent. consent.
Observable transport header information, together with information in Observable transport header information, together with information in
the network header, has been used to identify flows and their the network header, has been used to identify flows and their
connection state, together with the set of protocol options being connection state, together with the set of protocol options being
used. Transport protocols, such as TCP [RFC7414] and the Stream used. Transport protocols, such as TCP [RFC7414] and the Stream
Control Transport Protocol (SCTP) [RFC4960], specify a standard base Control Transmission Protocol (SCTP) [RFC4960], specify a standard
header that includes sequence number information and other data. base header that includes sequence number information and other data.
They also have the possibility to negotiate additional headers at They also have the possibility to negotiate additional headers at
connection setup, identified by an option number in the transport connection setup, identified by an option number in the transport
header. header.
In some uses, an assigned transport port (e.g., 0..49151) can In some uses, an assigned transport port (e.g., 0..49151) can
identify the upper-layer protocol or service [RFC7605]. However, identify the upper-layer protocol or service [RFC7605]. However,
port information alone is not sufficient to guarantee identification. port information alone is not sufficient to guarantee identification.
Applications can use arbitrary ports and do not need to use assigned Applications can use arbitrary ports and do not need to use assigned
port numbers. The use of an assigned port number is also not limited port numbers. The use of an assigned port number is also not limited
to the protocol for which the port is intended. Multiple sessions to the protocol for which the port is intended. Multiple sessions
can also be multiplexed on a single port, and ports can be re-used by can also be multiplexed on a single port, and ports can be reused by
subsequent sessions. subsequent sessions.
Some flows can be identified by observing signalling data (e.g., Some flows can be identified by observing signalling data (e.g., see
[RFC3261], [RFC8837]) or through the use of magic numbers placed in [RFC3261] and [RFC8837]) or through the use of magic numbers placed
the first byte(s) of a datagram payload [RFC7983]. in the first byte(s) of a datagram payload [RFC7983].
When transport header information cannot be observed, this removes When transport header information cannot be observed, this removes
information that could have been used to classify flows by passive information that could have been used to classify flows by passive
observers along the path. More ambitious ways could be used to observers along the path. More ambitious ways could be used to
collect, estimate, or infer flow information, including heuristics collect, estimate, or infer flow information, including heuristics
based on the analysis of traffic patterns, such as classification of based on the analysis of traffic patterns, such as classification of
flows relying on timing, volumes of information, and correlation flows relying on timing, volumes of information, and correlation
between multiple flows. For example, an operator that cannot access between multiple flows. For example, an operator that cannot access
the Session Description Protocol (SDP) session descriptions [RFC4566] the Session Description Protocol (SDP) session descriptions [RFC8866]
to classify a flow as audio traffic, might instead use (possibly to classify a flow as audio traffic might instead use (possibly less-
less-reliable) heuristics to infer that short UDP packets with reliable) heuristics to infer that short UDP packets with regular
regular spacing carry audio traffic. Operational practises aimed at spacing carry audio traffic. Operational practises aimed at
inferring transport parameters are out of scope for this document, inferring transport parameters are out of scope for this document,
and are only mentioned here to recognise that encryption does not and are only mentioned here to recognise that encryption does not
prevent operators from attempting to apply practises that were used prevent operators from attempting to apply practises that were used
with unencrypted transport headers. with unencrypted transport headers.
The IAB [RFC8546] have provided a summary of expected implications of The IAB [RFC8546] has provided a summary of expected implications of
increased encryption on network functions that use the observable increased encryption on network functions that use the observable
headers and describe the expected benefits of designs that explicitly headers and describe the expected benefits of designs that explicitly
declare protocol invariant header information that can be used for declare protocol-invariant header information that can be used for
this purpose. this purpose.
2.3. To Understand Transport Protocol Performance 2.3. To Understand Transport Protocol Performance
This subsection describes use by the network of exposed transport This subsection describes use by the network of exposed transport-
layer headers to understand transport protocol performance and layer headers to understand transport protocol performance and
behaviour. behaviour.
2.3.1. Using Information Derived from Transport Layer Headers 2.3.1. Using Information Derived from Transport-Layer Headers
Observable transport headers enable explicit measurement and analysis Observable transport headers enable explicit measurement and analysis
of protocol performance, and detection of network anomalies at any of protocol performance and detection of network anomalies at any
point along the Internet path. Some operators use passive monitoring point along the Internet path. Some operators use passive monitoring
to manage their portion of the Internet by characterising the to manage their portion of the Internet by characterising the
performance of link/network segments. Inferences from transport performance of link/network segments. Inferences from transport
headers are used to derive performance metrics: headers are used to derive performance metrics:
Traffic Rate and Volume: Per-application traffic rate and volume Traffic Rate and Volume:
measures can be used to characterise the traffic that uses a Per-application traffic rate and volume measures can be used to
network segment or the pattern of network usage. Observing the characterise the traffic that uses a network segment or the
protocol sequence number and packet size offers one way to measure pattern of network usage. Observing the protocol sequence number
this (e.g., measurements observing counters in periodic reports and packet size offers one way to measure this (e.g., measurements
such as RTCP; or measurements observing protocol sequence numbers observing counters in periodic reports, such as RTCP [RFC3550]
in statistical samples of packet flows, or specific control [RFC3711] [RFC4585], or measurements observing protocol sequence
numbers in statistical samples of packet flows or specific control
packets, such as those observed at the start and end of a flow). packets, such as those observed at the start and end of a flow).
Measurements can be per endpoint, or for an endpoint aggregate. Measurements can be per endpoint or for an endpoint aggregate.
These could be used to assess usage or for subscriber billing. These could be used to assess usage or for subscriber billing.
Such measurements can be used to trigger traffic shaping, and to Such measurements can be used to trigger traffic shaping and to
associate QoS support within the network and lower layers. This associate QoS support within the network and lower layers. This
can be done with consent and in support of an end user, to improve can be done with consent and in support of an end user to improve
quality of service; or could be used by the network to de- quality of service or could be used by the network to deprioritise
prioritise certain flows without user consent. certain flows without user consent.
The traffic rate and volume can be determined providing that the The traffic rate and volume can be determined, providing that the
packets belonging to individual flows can be identified, but there packets belonging to individual flows can be identified, but there
might be no additional information about a flow when the transport might be no additional information about a flow when the transport
headers cannot be observed. headers cannot be observed.
Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g., Loss Rate and Loss Pattern:
from transport sequence numbers or inferred from observing Flow loss rate can be derived (e.g., from transport sequence
transport protocol interactions) and has been used as a metric for numbers or inferred from observing transport protocol
performance assessment and to characterise transport behaviour. interactions) and has been used as a metric for performance
Network operators have used the variation in patterns to detect assessment and to characterise transport behaviour. Network
changes in the offered service. Understanding the location and operators have used the variation in patterns to detect changes in
root cause of loss can help an operator determine whether this the offered service. Understanding the location and root cause of
requires corrective action. loss can help an operator determine whether this requires
corrective action.
There are various causes of loss, including: corruption of link There are various causes of loss, including: corruption of link
frames (e.g., due to interference on a radio link), buffering loss frames (e.g., due to interference on a radio link); buffering loss
(e.g., overflow due to congestion, Active Queue Management, AQM (e.g., overflow due to congestion, Active Queue Management (AQM)
[RFC7567], or inadequate provision following traffic pre-emption), [RFC7567], or inadequate provision following traffic preemption),
and policing (traffic management [RFC2475]). Understanding flow and policing (e.g., traffic management [RFC2475]). Understanding
loss rates requires maintaining per-flow state (flow flow loss rates requires maintaining the per-flow state (flow
identification often requires transport layer information) and identification often requires transport-layer information) and
either observing the increase in sequence numbers in the network either observing the increase in sequence numbers in the network
or transport headers, or comparing a per-flow packet counter with or transport headers or comparing a per-flow packet counter with
the number of packets that the flow actually sent. Per-hop loss the number of packets that the flow actually sent. Per-hop loss
can also sometimes be monitored at the interface level by devices can also sometimes be monitored at the interface level by devices
on the network path, or using in-situ methods operating over a on the network path or by using in-situ methods operating over a
network segment (see Section 3.3). network segment (see Section 3.3).
The pattern of loss can provide insight into the cause of loss. The pattern of loss can provide insight into the cause of loss.
Losses can often occur as bursts, randomly-timed events, etc. It Losses can often occur as bursts, randomly timed events, etc. It
can also be valuable to understand the conditions under which loss can also be valuable to understand the conditions under which loss
occurs. This usually requires relating loss to the traffic occurs. This usually requires relating loss to the traffic
flowing at a network node or segment at the time of loss. flowing at a network node or segment at the time of loss.
Transport header information can help identify cases where loss Transport header information can help identify cases where loss
could have been wrongly identified, or where the transport did not could have been wrongly identified or where the transport did not
require retransmission of a lost packet. require retransmission of a lost packet.
Throughput and Goodput: Throughput is the amount of payload data Throughput and Goodput:
sent by a flow per time interval. Goodput (the subset of Throughput is the amount of payload data sent by a flow per time
throughput consisting of useful traffic) (see Section 2.5 of interval. Goodput (the subset of throughput consisting of useful
[RFC7928] and [RFC5166]) is a measure of useful data exchanged. traffic; see Section 2.5 of [RFC7928] and [RFC5166]) is a measure
The throughput of a flow can be determined in the absence of of useful data exchanged. The throughput of a flow can be
transport header information, providing that the individual flow determined in the absence of transport header information,
can be identified, and the overhead known. Goodput requires providing that the individual flow can be identified, and the
ability to differentiate loss and retransmission of packets, for overhead known. Goodput requires the ability to differentiate
example by observing packet sequence numbers in the TCP or RTP loss and retransmission of packets, for example, by observing
headers [RFC3550]. packet sequence numbers in the TCP or RTP headers [RFC3550].
Latency: Latency is a key performance metric that impacts Latency:
application and user-perceived response times. It often Latency is a key performance metric that impacts application and
indirectly impacts throughput and flow completion time. This user-perceived response times. It often indirectly impacts
determines the reaction time of the transport protocol itself, throughput and flow completion time. This determines the reaction
impacting flow setup, congestion control, loss recovery, and other time of the transport protocol itself, impacting flow setup,
transport mechanisms. The observed latency can have many congestion control, loss recovery, and other transport mechanisms.
components [Latency]. Of these, unnecessary/unwanted queueing in The observed latency can have many components [Latency]. Of
buffers of the network devices on the path has often been observed these, unnecessary/unwanted queueing in buffers of the network
as a significant factor [bufferbloat]. Once the cause of unwanted devices on the path has often been observed as a significant
latency has been identified, this can often be eliminated. factor [bufferbloat]. Once the cause of unwanted latency has been
identified, this can often be eliminated.
To measure latency across a part of a path, an observation point To measure latency across a part of a path, an observation point
[RFC7799] can measure the experienced round trip time (RTT) using [RFC7799] can measure the experienced round-trip time (RTT) by
packet sequence numbers and acknowledgements, or by observing using packet sequence numbers and acknowledgements or by observing
header timestamp information. Such information allows an header timestamp information. Such information allows an
observation point on the network path to determine not only the observation point on the network path to determine not only the
path RTT, but also allows measurement of the upstream and path RTT but also allows measurement of the upstream and
downstream contribution to the RTT. This could be used to locate downstream contribution to the RTT. This could be used to locate
a source of latency, e.g., by observing cases where the median RTT a source of latency, e.g., by observing cases where the median RTT
is much greater than the minimum RTT for a part of a path. is much greater than the minimum RTT for a part of a path.
The service offered by network operators can benefit from latency The service offered by network operators can benefit from latency
information to understand the impact of configuration changes and information to understand the impact of configuration changes and
to tune deployed services. Latency metrics are key to evaluating to tune deployed services. Latency metrics are key to evaluating
and deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit and deploying AQM [RFC7567], Diffserv [RFC2474], and Explicit
Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements
could identify excessively large buffers, indicating where to could identify excessively large buffers, indicating where to
deploy or configure AQM. An AQM method is often deployed in deploy or configure AQM. An AQM method is often deployed in
combination with other techniques, such as scheduling [RFC7567] combination with other techniques, such as scheduling [RFC7567]
[RFC8290] and although parameter-less methods are desired [RFC8290], and although parameter-less methods are desired
[RFC7567], current methods often require tuning [RFC8290] [RFC7567], current methods often require tuning [RFC8290]
[RFC8289] [RFC8033] because they cannot scale across all possible [RFC8289] [RFC8033] because they cannot scale across all possible
deployment scenarios. deployment scenarios.
Latency and round-trip time information can potentially expose Latency and round-trip time information can potentially expose
some information useful for approximate geolocation, as discussed some information useful for approximate geolocation, as discussed
in [PAM-RTT]. in [PAM-RTT].
Variation in delay: Some network applications are sensitive to Variation in Delay:
(small) changes in packet timing (jitter). Short and long-term Some network applications are sensitive to (small) changes in
delay variation can impact on the latency of a flow and hence the packet timing (jitter). Short- and long-term delay variation can
perceived quality of applications using a network path. For impact the latency of a flow and hence the perceived quality of
example, jitter metrics are often cited when characterising paths applications using a network path. For example, jitter metrics
supporting real-time traffic. The expected performance of such are often cited when characterising paths supporting real-time
applications, can be inferred from a measure of the variation in traffic. The expected performance of such applications can be
delay observed along a portion of the path [RFC3393] [RFC5481]. inferred from a measure of the variation in delay observed along a
The requirements resemble those for the measurement of latency. portion of the path [RFC3393] [RFC5481]. The requirements
resemble those for the measurement of latency.
Flow Reordering: Significant packet reordering within a flow can Flow Reordering:
impact time-critical applications and can be interpreted as loss Significant packet reordering within a flow can impact time-
by reliable transports. Many transport protocol techniques are critical applications and can be interpreted as loss by reliable
impacted by reordering (e.g., triggering TCP retransmission or re- transports. Many transport protocol techniques are impacted by
buffering of real-time applications). Packet reordering can occur reordering (e.g., triggering TCP retransmission or rebuffering of
for many reasons, from equipment design to misconfiguration of real-time applications). Packet reordering can occur for many
reasons, e.g., from equipment design to misconfiguration of
forwarding rules. Flow identification is often required to avoid forwarding rules. Flow identification is often required to avoid
significant packet mis-ordering (e.g., when using ECMP, or LAG). significant packet misordering (e.g., when using ECMP, or LAG).
Network tools can detect and measure unwanted/excessive Network tools can detect and measure unwanted/excessive reordering
reordering, and the impact on transport performance. and the impact on transport performance.
There have been initiatives in the IETF transport area to reduce There have been initiatives in the IETF transport area to reduce
the impact of reordering within a transport flow, possibly leading the impact of reordering within a transport flow, possibly leading
to a reduction in the requirements for preserving ordering. These to a reduction in the requirements for preserving ordering. These
have potential to simplify network equipment design as well as the have potential to simplify network equipment design as well as the
potential to improve robustness of the transport service. potential to improve robustness of the transport service.
Measurements of reordering can help understand the present level Measurements of reordering can help understand the present level
of reordering, and inform decisions about how to progress new of reordering and inform decisions about how to progress new
mechanisms. mechanisms.
Techniques for measuring reordering typically observe packet Techniques for measuring reordering typically observe packet
sequence numbers. Metrics have been defined that evaluate whether sequence numbers. Metrics have been defined that evaluate whether
a network path has maintained packet order on a packet-by-packet a network path has maintained packet order on a packet-by-packet
basis [RFC4737] [RFC5236]. Some protocols provide in-built basis [RFC4737] [RFC5236]. Some protocols provide in-built
monitoring and reporting functions. Transport fields in the RTP monitoring and reporting functions. Transport fields in the RTP
header [RFC3550] [RFC4585] can be observed to derive traffic header [RFC3550] [RFC4585] can be observed to derive traffic
volume measurements and provide information on the progress and volume measurements and provide information on the progress and
quality of a session using RTP. Metadata assists in understanding quality of a session using RTP. Metadata assists in understanding
the context under which the data was collected, including the the context under which the data was collected, including the
time, observation point [RFC7799], and way in which metrics were time, observation point [RFC7799], and way in which metrics were
accumulated. The RTCP protocol directly reports some of this accumulated. The RTCP protocol directly reports some of this
information in a form that can be directly visible by devices on information in a form that can be directly visible by devices on
the network path. the network path.
In some cases, measurements could involve active injection of test In some cases, measurements could involve active injection of test
traffic to perform a measurement (see Section 3.4 of [RFC7799]). traffic to perform a measurement (see Section 3.4 of [RFC7799]).
However, most operators do not have access to user equipment, However, most operators do not have access to user equipment;
therefore the point of test is normally different from the transport therefore, the point of test is normally different from the transport
endpoint. Injection of test traffic can incur an additional cost in endpoint. Injection of test traffic can incur an additional cost in
running such tests (e.g., the implications of capacity tests in a running such tests (e.g., the implications of capacity tests in a
mobile network segment are obvious). Some active measurements mobile network segment are obvious). Some active measurements
[RFC7799] (e.g., response under load or particular workloads) perturb [RFC7799] (e.g., response under load or particular workloads) perturb
other traffic, and could require dedicated access to the network other traffic and could require dedicated access to the network
segment. segment.
Passive measurements (see Section 3.6 of [RFC7799]) can have Passive measurements (see Section 3.6 of [RFC7799]) can have
advantages in terms of eliminating unproductive test traffic, advantages in terms of eliminating unproductive test traffic,
reducing the influence of test traffic on the overall traffic mix, reducing the influence of test traffic on the overall traffic mix,
and the ability to choose the point of observation (see and having the ability to choose the point of observation (see
Section 2.4.1). Measurements can rely on observing packet headers, Section 2.4.1). Measurements can rely on observing packet headers,
which is not possible if those headers are encrypted, but could which is not possible if those headers are encrypted, but could
utilise information about traffic volumes or patterns of interaction utilise information about traffic volumes or patterns of interaction
to deduce metrics. to deduce metrics.
Passive packet sampling techniques are also often used to scale the Passive packet sampling techniques are also often used to scale the
processing involved in observing packets on high rate links. This processing involved in observing packets on high-rate links. This
exports only the packet header information of (randomly) selected exports only the packet header information of (randomly) selected
packets. Interpretation of the exported information relies on packets. Interpretation of the exported information relies on
understanding of the header information. The utility of these understanding of the header information. The utility of these
measurements depends on the type of network segment/link and number measurements depends on the type of network segment/link and number
of mechanisms used by the network devices. Simple routers are of mechanisms used by the network devices. Simple routers are
relatively easy to manage, but a device with more complexity demands relatively easy to manage, but a device with more complexity demands
understanding of the choice of many system parameters. understanding of the choice of many system parameters.
2.3.2. Using Information Derived from Network Layer Header Fields 2.3.2. Using Information Derived from Network-Layer Header Fields
Information from the transport header can be used by a multi-field Information from the transport header can be used by a multi-field
(MF) classifier as a part of policy framework. Policies are commonly (MF) classifier as a part of policy framework. Policies are commonly
used for management of the QoS or Quality of Experience (QoE) in used for management of the QoS or Quality of Experience (QoE) in
resource-constrained networks, or by firewalls to implement access resource-constrained networks or by firewalls to implement access
rules (see also Section 2.2.2 of [RFC8404]). Policies can support rules (see also Section 2.2.2 of [RFC8404]). Policies can support
user applications/services or protect against unwanted, or lower user applications/services or protect against unwanted or lower-
priority traffic (Section 2.4.4). priority traffic (Section 2.4.4).
Transport layer information can also be explicitly carried in Transport-layer information can also be explicitly carried in
network-layer header fields that are not encrypted, serving as a network-layer header fields that are not encrypted, serving as a
replacement/addition to the exposed transport header information replacement/addition to the exposed transport header information
[RFC8558]. This information can enable a different forwarding [RFC8558]. This information can enable a different forwarding
treatment by the devices forming the network path, even when a treatment by the devices forming the network path, even when a
transport employs encryption to protect other header information. transport employs encryption to protect other header information.
On the one hand, the user of a transport that multiplexes multiple On the one hand, the user of a transport that multiplexes multiple
sub-flows might want to obscure the presence and characteristics of subflows might want to obscure the presence and characteristics of
these sub-flows. On the other hand, an encrypted transport could set these subflows. On the other hand, an encrypted transport could set
the network-layer information to indicate the presence of sub-flows, the network-layer information to indicate the presence of subflows
and to reflect the service requirements of individual sub-flows. and to reflect the service requirements of individual subflows.
There are several ways this could be done: There are several ways this could be done:
IP Address: Applications normally expose the endpoint addresses used IP Address:
in the forwarding decisions in network devices. Address and other Applications normally expose the endpoint addresses used in the
protocol information can be used by a MF-classifier to determine forwarding decisions in network devices. Address and other
how traffic is treated [RFC2475], and hence affect the quality of protocol information can be used by an MF classifier to determine
how traffic is treated [RFC2475] and hence affects the quality of
experience for a flow. Common issues concerning IP address experience for a flow. Common issues concerning IP address
sharing are described in [RFC6269]. sharing are described in [RFC6269].
Using the IPv6 Network-Layer Flow Label: A number of Standards Track Using the IPv6 Network-Layer Flow Label:
and Best Current Practice RFCs (e.g., [RFC8085], [RFC6437], A number of Standards Track and Best Current Practice RFCs (e.g.,
[RFC6438]) encourage endpoints to set the IPv6 flow label field of [RFC8085], [RFC6437], and [RFC6438]) encourage endpoints to set
the network-layer header. IPv6 "source nodes SHOULD assign each the IPv6 Flow Label field of the network-layer header. As per
unrelated transport connection and application data stream to a [RFC6437], IPv6 source nodes "SHOULD assign each unrelated
new flow" [RFC6437]. A multiplexing transport could choose to use transport connection and application data stream to a new flow."
multiple flow labels to allow the network to independently forward A multiplexing transport could choose to use multiple flow labels
sub-flows. RFC6437 provides further guidance on choosing a flow to allow the network to independently forward subflows. [RFC6437]
label value, stating these "should be chosen such that their bits provides further guidance on choosing a flow label value, stating
exhibit a high degree of variability", and chosen so that "third these "should be chosen such that their bits exhibit a high degree
parties should be unlikely to be able to guess the next value that of variability" and chosen so that "third parties should be
a source of flow labels will choose". unlikely to be able to guess the next value that a source of flow
labels will choose."
Once set, a flow label can provide information that can help Once set, a flow label can provide information that can help
inform network-layer queueing and forwarding, including use with inform network-layer queueing and forwarding, including use with
IPsec, [RFC6294] and use with Equal Cost Multi-Path routing and IPsec [RFC6294], Equal-Cost Multipath routing, and Link
Link Aggregation[RFC6438]. Aggregation [RFC6438].
The choice of how to assign a flow label needs to avoid The choice of how to assign a flow label needs to avoid
introducing linkages between flows that a network device could not introducing linkages between flows that a network device could not
otherwise observe. Inappropriate use by the transport can have otherwise observe. Inappropriate use by the transport can have
privacy implications (e.g., assigning the same label to two privacy implications (e.g., assigning the same label to two
independent flows that ought not to be classified the same). independent flows that ought not to be classified similarly).
Using the Network-Layer Differentiated Services Code Point: Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to network Applications can expose their delivery expectations to network
devices by setting the Differentiated Services Code Point (DSCP) devices by setting the Differentiated Services Code Point (DSCP)
field of IPv4 and IPv6 packets [RFC2474]. For example, WebRTC field of IPv4 and IPv6 packets [RFC2474]. For example, WebRTC
applications identify different forwarding treatments for applications identify different forwarding treatments for
individual sub-flows (audio vs. video) based on the value of the individual subflows (audio vs. video) based on the value of the
DSCP field [I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit DSCP field [RFC8837]). This provides explicit information to
information to inform network-layer queueing and forwarding, inform network-layer queueing and forwarding, rather than an
rather than an operator inferring traffic requirements from operator inferring traffic requirements from transport and
transport and application headers via a multi-field classifier. application headers via a multi-field classifier. Inappropriate
Inappropriate use by the transport can have privacy implications use by the transport can have privacy implications (e.g.,
(e.g., assigning a different DSCP to a subflow could assist in a assigning a different DSCP to a subflow could assist in a network
network device discovering the traffic pattern used by an device discovering the traffic pattern used by an application).
application). The field is mutable, i.e., some network devices The field is mutable, i.e., some network devices can be expected
can be expected to change this field. Since the DSCP value can to change this field. Since the DSCP value can impact the quality
impact the quality of experience for a flow, observations of of experience for a flow, observations of service performance have
service performance have to consider this field when a network to consider this field when a network path supports differentiated
path supports differentiated service treatment. service treatment.
Using Explicit Congestion Marking: ECN [RFC3168] is a transport Using Explicit Congestion Notification:
Explicit Congestion Notification (ECN) [RFC3168] is a transport
mechanism that uses the ECN field in the network-layer header. mechanism that uses the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport Use of ECN explicitly informs the network layer that a transport
is ECN-capable, and requests ECN treatment of the flow. An ECN- is ECN capable and requests ECN treatment of the flow. An ECN-
capable transport can offer benefits when used over a path with capable transport can offer benefits when used over a path with
equipment that implements an AQM method with CE marking of IP equipment that implements an AQM method with Congestion
packets [RFC8087], since it can react to congestion without also Experienced (CE) marking of IP packets [RFC8087], since it can
having to recover from lost packets. react to congestion without also having to recover from lost
packets.
ECN exposes the presence of congestion. The reception of CE- ECN exposes the presence of congestion. The reception of CE-
marked packets can be used to estimate the level of incipient marked packets can be used to estimate the level of incipient
congestion on the upstream portion of the path from the point of congestion on the upstream portion of the path from the point of
observation (Section 2.5 of [RFC8087]). Interpreting the marking observation (Section 2.5 of [RFC8087]). Interpreting the marking
behaviour (i.e., assessing congestion and diagnosing faults) behaviour (i.e., assessing congestion and diagnosing faults)
requires context from the transport layer, such as path RTT. requires context from the transport layer, such as path RTT.
AQM and ECN offer a range of algorithms and configuration options. AQM and ECN offer a range of algorithms and configuration options.
Tools therefore have to be available to network operators and Tools therefore have to be available to network operators and
researchers to understand the implication of configuration choices researchers to understand the implication of configuration choices
and transport behaviour as the use of ECN increases and new and transport behaviour as the use of ECN increases and new
methods emerge [RFC7567]. methods emerge [RFC7567].
Network-Layer Options Network protocols can carry optional headers Network-Layer Options:
(see Section 5.1). These can explicitly expose transport header Network protocols can carry optional headers (see Section 5.1).
information to on-path devices operating at the network layer (as These can explicitly expose transport header information to on-
discussed further in Section 6). path devices operating at the network layer (as discussed further
in Section 6).
IPv4 [RFC0791] has provision for optional header fields. IP IPv4 [RFC0791] has provisions for optional header fields. IP
routers can examine these headers and are required to ignore IPv4 routers can examine these headers and are required to ignore IPv4
options that they do not recognise. Many current paths include options that they do not recognise. Many current paths include
network devices that forward packets that carry options on a network devices that forward packets that carry options on a
slower processing path. Some network devices (e.g., firewalls) slower processing path. Some network devices (e.g., firewalls)
can be (and are) configured to drop these packets [RFC7126]. BCP can be (and are) configured to drop these packets [RFC7126]. BCP
186 [RFC7126] provides Best Current Practice guidance on how 186 [RFC7126] provides guidance on how operators should treat IPv4
operators should treat IPv4 packets that specify options. packets that specify options.
IPv6 can encode optional network-layer information in separate IPv6 can encode optional network-layer information in separate
headers that may be placed between the IPv6 header and the upper- headers that may be placed between the IPv6 header and the upper-
layer header [RFC8200]. (e.g., the IPv6 Alternate Marking Method layer header [RFC8200] (e.g., the IPv6 Alternate Marking Method
[I-D.ietf-6man-ipv6-alt-mark], which can be used to measure packet [IPV6-ALT-MARK], which can be used to measure packet loss and
loss and delay metrics). The Hop-by-Hop options header, when delay metrics). The Hop-by-Hop Options header, when present,
present, immediately follows the IPv6 header. IPv6 permits this immediately follows the IPv6 header. IPv6 permits this header to
header to be examined by any node along the path if explicitly be examined by any node along the path if explicitly configured
configured [RFC8200]. [RFC8200].
Careful use of the network layer features (e.g., Extension Headers Careful use of the network-layer features (e.g., extension headers
can Section 5) help provide similar information in the case where the can; see Section 5) help provide similar information in the case
network is unable to inspect transport protocol headers. where the network is unable to inspect transport protocol headers.
2.4. To Support Network Operations 2.4. To Support Network Operations
Some network operators make use of on-path observations of transport Some network operators make use of on-path observations of transport
headers to analyse the service offered to the users of a network headers to analyse the service offered to the users of a network
segment, and to inform operational practice, and can help detect and segment and inform operational practice and can help detect and
locate network problems. [RFC8517] gives an operator's perspective locate network problems. [RFC8517] gives an operator's perspective
about such use. about such use.
When observable transport header information is not available, those When observable transport header information is not available, those
seeking an understanding of transport behaviour and dynamics might seeking an understanding of transport behaviour and dynamics might
learn to work without that information. Alternatively, they might learn to work without that information. Alternatively, they might
use more limited measurements combined with pattern inference and use more limited measurements combined with pattern inference and
other heuristics to infer network behaviour (see Section 2.1.1 of other heuristics to infer network behaviour (see Section 2.1.1 of
[RFC8404]). Operational practises aimed at inferring transport [RFC8404]). Operational practises aimed at inferring transport
parameters are out of scope for this document, and are only mentioned parameters are out of scope for this document and are only mentioned
here to recognise that encryption does not necessarily stop operators here to recognise that encryption does not necessarily stop operators
from attempting to apply practises that have been used with from attempting to apply practises that have been used with
unencrypted transport headers. unencrypted transport headers.
This section discusses topics concerning observation of transport This section discusses topics concerning observation of transport
flows, with a focus on transport measurement. flows, with a focus on transport measurement.
2.4.1. Problem Location 2.4.1. Problem Location
Observations of transport header information can be used to locate Observations of transport header information can be used to locate
the source of problems or to assess the performance of a network the source of problems or to assess the performance of a network
segment. Often issues can only be understood in the context of the segment. Often issues can only be understood in the context of the
other flows that share a particular path, particular device other flows that share a particular path, particular device
configuration, interface port, etc. A simple example is monitoring configuration, interface port, etc. A simple example is monitoring
of a network device that uses a scheduler or active queue management of a network device that uses a scheduler or active queue management
technique [RFC7567], where it could be desirable to understand technique [RFC7567], where it could be desirable to understand
whether the algorithms are correctly controlling latency, or if whether the algorithms are correctly controlling latency or if
overload protection is working. This implies knowledge of how overload protection is working. This implies knowledge of how
traffic is assigned to any sub-queues used for flow scheduling, but traffic is assigned to any subqueues used for flow scheduling but can
can require information about how the traffic dynamics impact active require information about how the traffic dynamics impact active
queue management, starvation prevention mechanisms, and circuit- queue management, starvation prevention mechanisms, and circuit
breakers. breakers.
Sometimes correlating observations of headers at multiple points Sometimes correlating observations of headers at multiple points
along the path (e.g., at the ingress and egress of a network along the path (e.g., at the ingress and egress of a network segment)
segment), allows an observer to determine the contribution of a allows an observer to determine the contribution of a portion of the
portion of the path to an observed metric. e.g., to locate a source path to an observed metric (e.g., to locate a source of delay,
of delay, jitter, loss, reordering, or congestion marking. jitter, loss, reordering, or congestion marking).
2.4.2. Network Planning and Provisioning 2.4.2. Network Planning and Provisioning
Traffic rate and volume measurements are used to help plan deployment Traffic rate and volume measurements are used to help plan deployment
of new equipment and configuration in networks. Data is also of new equipment and configuration in networks. Data is also
valuable to equipment vendors who want to understand traffic trends valuable to equipment vendors who want to understand traffic trends
and patterns of usage as inputs to decisions about planning products and patterns of usage as inputs to decisions about planning products
and provisioning for new deployments. and provisioning for new deployments.
Trends in aggregate traffic can be observed and can be related to the Trends in aggregate traffic can be observed and can be related to the
skipping to change at page 14, line 42 skipping to change at line 659
network use, applications, and user characteristics. In general, network use, applications, and user characteristics. In general,
when only a small proportion of the traffic has a specific when only a small proportion of the traffic has a specific
(different) characteristic, such traffic seldom leads to operational (different) characteristic, such traffic seldom leads to operational
concern, although the ability to measure and monitor it is lower. concern, although the ability to measure and monitor it is lower.
The desire to understand the traffic and protocol interactions The desire to understand the traffic and protocol interactions
typically grows as the proportion of traffic increases. The typically grows as the proportion of traffic increases. The
challenges increase when multiple instances of an evolving protocol challenges increase when multiple instances of an evolving protocol
contribute to the traffic that share network capacity. contribute to the traffic that share network capacity.
Operators can manage traffic load (e.g., when the network is severely Operators can manage traffic load (e.g., when the network is severely
overloaded) by deploying rate-limiters, traffic shaping, or network overloaded) by deploying rate limiters, traffic shaping, or network
transport circuit breakers [RFC8084]. The information provided by transport circuit breakers [RFC8084]. The information provided by
observing transport headers is a source of data that can help to observing transport headers is a source of data that can help to
inform such mechanisms. inform such mechanisms.
Congestion Control Compliance of Traffic: Congestion control is a Congestion Control Compliance of Traffic:
key transport function [RFC2914]. Many network operators Congestion control is a key transport function [RFC2914]. Many
implicitly accept that TCP traffic complies with a behaviour that network operators implicitly accept that TCP traffic complies with
is acceptable for the shared Internet. TCP algorithms have been a behaviour that is acceptable for the shared Internet. TCP
continuously improved over decades, and have reached a level of algorithms have been continuously improved over decades and have
efficiency and correctness that is difficult to match in custom reached a level of efficiency and correctness that is difficult to
application-layer mechanisms [RFC8085]. match in custom application-layer mechanisms [RFC8085].
A standards-compliant TCP stack provides congestion control that A standards-compliant TCP stack provides congestion control that
is judged safe for use across the Internet. Applications is judged safe for use across the Internet. Applications
developed on top of well-designed transports can be expected to developed on top of well-designed transports can be expected to
appropriately control their network usage, reacting when the appropriately control their network usage, reacting when the
network experiences congestion, by back-off and reduce the load network experiences congestion, by backing off and reducing the
placed on the network. This is the normal expected behaviour for load placed on the network. This is the normal expected behaviour
IETF-specified transports (e.g., TCP and SCTP). for IETF-specified transports (e.g., TCP and SCTP).
Congestion Control Compliance for UDP traffic: UDP provides a Congestion Control Compliance for UDP Traffic:
minimal message-passing datagram transport that has no inherent UDP provides a minimal message-passing datagram transport that has
congestion control mechanisms. Because congestion control is no inherent congestion control mechanisms. Because congestion
critical to the stable operation of the Internet, applications and control is critical to the stable operation of the Internet,
other protocols that choose to use UDP as a transport have to applications and other protocols that choose to use UDP as a
employ mechanisms to prevent collapse, avoid unacceptable transport have to employ mechanisms to prevent collapse, avoid
contributions to jitter/latency, and to establish an acceptable unacceptable contributions to jitter/latency, and establish an
share of capacity with concurrent traffic [RFC8085]. acceptable share of capacity with concurrent traffic [RFC8085].
UDP flows that expose a well-known header can be observed to gain UDP flows that expose a well-known header can be observed to gain
understanding of the dynamics of a flow and its congestion control understanding of the dynamics of a flow and its congestion control
behaviour. For example, tools exist to monitor various aspects of behaviour. For example, tools exist to monitor various aspects of
RTP header information and RTCP reports for real-time flows (see RTP header information and RTCP reports for real-time flows (see
Section 2.3). The Secure RTP and RTCP extensions [RFC3711] were Section 2.3). The Secure RTP and RTCP extensions [RFC3711] were
explicitly designed to expose some header information to enable explicitly designed to expose some header information to enable
such observation, while protecting the payload data. such observation while protecting the payload data.
A network operator can observe the headers of transport protocols A network operator can observe the headers of transport protocols
layered above UDP to understand if the datagram flows comply with layered above UDP to understand if the datagram flows comply with
congestion control expectations. This can help inform a decision congestion control expectations. This can help inform a decision
on whether it might be appropriate to deploy methods such as rate- on whether it might be appropriate to deploy methods, such as rate
limiters to enforce acceptable usage. The available information limiters, to enforce acceptable usage. The available information
determines the level of precision with which flows can be determines the level of precision with which flows can be
classified and the design space for conditioning mechanisms (e.g., classified and the design space for conditioning mechanisms (e.g.,
rate limiting, circuit breaker techniques [RFC8084], or blocking rate-limiting, circuit breaker techniques [RFC8084], or blocking
of uncharacterised traffic) [RFC5218]. uncharacterised traffic) [RFC5218].
When anomalies are detected, tools can interpret the transport header When anomalies are detected, tools can interpret the transport header
information to help understand the impact of specific transport information to help understand the impact of specific transport
protocols (or protocol mechanisms) on the other traffic that shares a protocols (or protocol mechanisms) on the other traffic that shares a
network. An observer on the network path can gain an understanding network. An observer on the network path can gain an understanding
of the dynamics of a flow and its congestion control behaviour. of the dynamics of a flow and its congestion control behaviour.
Analysing observed flows can help to build confidence that an Analysing observed flows can help to build confidence that an
application flow backs-off its share of the network load under application flow backs off its share of the network load under
persistent congestion, and hence to understand whether the behaviour persistent congestion and hence to understand whether the behaviour
is appropriate for sharing limited network capacity. For example, it is appropriate for sharing limited network capacity. For example, it
is common to visualise plots of TCP sequence numbers versus time for is common to visualise plots of TCP sequence numbers versus time for
a flow to understand how a flow shares available capacity, deduce its a flow to understand how a flow shares available capacity, deduce its
dynamics in response to congestion, etc. dynamics in response to congestion, etc.
The ability to identify sources and flows that contribute to The ability to identify sources and flows that contribute to
persistent congestion is important to the safe operation of network persistent congestion is important to the safe operation of network
infrastructure, and can inform configuration of network devices to infrastructure and can inform configuration of network devices to
complement the endpoint congestion avoidance mechanisms [RFC7567] complement the endpoint congestion avoidance mechanisms [RFC7567]
[RFC8084] to avoid a portion of the network being driven into [RFC8084] to avoid a portion of the network being driven into
congestion collapse [RFC2914]. congestion collapse [RFC2914].
2.4.4. To Characterise "Unknown" Network Traffic 2.4.4. To Characterise "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity change The patterns and types of traffic that share Internet capacity change
over time as networked applications, usage patterns and protocols over time as networked applications, usage patterns, and protocols
continue to evolve. continue to evolve.
Encryption can increase the volume of "unknown" or "uncharacterised" Encryption can increase the volume of "unknown" or "uncharacterised"
traffic seen by the network. If these traffic patterns form a small traffic seen by the network. If these traffic patterns form a small
part of the traffic aggregate passing through a network device or part of the traffic aggregate passing through a network device or
segment of the network path, the dynamics of the uncharacterised segment of the network path, the dynamics of the uncharacterised
traffic might not have a significant collateral impact on the traffic might not have a significant collateral impact on the
performance of other traffic that shares this network segment. Once performance of other traffic that shares this network segment. Once
the proportion of this traffic increases, monitoring the traffic can the proportion of this traffic increases, monitoring the traffic can
determine if appropriate safety measures have to be put in place. determine if appropriate safety measures have to be put in place.
skipping to change at page 16, line 48 skipping to change at line 761
2.4.5. To Support Network Security Functions 2.4.5. To Support Network Security Functions
On-path observation of the transport headers of packets can be used On-path observation of the transport headers of packets can be used
for various security functions. For example, Denial of Service (DoS) for various security functions. For example, Denial of Service (DoS)
and Distributed DoS (DDoS) attacks against the infrastructure or and Distributed DoS (DDoS) attacks against the infrastructure or
against an endpoint can be detected and mitigated by characterising against an endpoint can be detected and mitigated by characterising
anomalous traffic (see Section 2.4.4) on a shorter timescale. Other anomalous traffic (see Section 2.4.4) on a shorter timescale. Other
uses include support for security audits (e.g., verifying the uses include support for security audits (e.g., verifying the
compliance with cipher suites), client and application fingerprinting compliance with cipher suites), client and application fingerprinting
for inventory, and to provide alerts for network intrusion detection for inventory, and alerts provided for network intrusion detection
and other next generation firewall functions. and other next generation firewall functions.
When using an encrypted transport, endpoints can directly provide When using an encrypted transport, endpoints can directly provide
information to support these security functions. Another method, if information to support these security functions. Another method, if
the endpoints do not provide this information, is to use an on-path the endpoints do not provide this information, is to use an on-path
network device that relies on pattern inferences in the traffic, and network device that relies on pattern inferences in the traffic and
heuristics or machine learning instead of processing observed header heuristics or machine learning instead of processing observed header
information. An endpoint could also explicitly cooperate with an on- information. An endpoint could also explicitly cooperate with an on-
path device (e.g., a QUIC endpoint could share information about path device (e.g., a QUIC endpoint could share information about
current uses of connection IDs). current uses of connection IDs).
2.4.6. Network Diagnostics and Troubleshooting 2.4.6. Network Diagnostics and Troubleshooting
Operators monitor the health of a network segment to support a Operators monitor the health of a network segment to support a
variety of operational tasks [RFC8404] including procedures to variety of operational tasks [RFC8404], including procedures to
provide early warning and trigger action: to diagnose network provide early warning and trigger action, e.g., to diagnose network
problems, to manage security threats (including DoS), to evaluate problems, to manage security threats (including DoS), to evaluate
equipment or protocol performance, or to respond to user performance equipment or protocol performance, or to respond to user performance
questions. Information about transport flows can assist in setting questions. Information about transport flows can assist in setting
buffer sizes, and help identify whether link/network tuning is buffer sizes and help identify whether link/network tuning is
effective. Information can also support debugging and diagnosis of effective. Information can also support debugging and diagnosis of
the root causes of faults that concern a particular user's traffic the root causes of faults that concern a particular user's traffic
and can support post-mortem investigation after an anomaly. and can support postmortem investigation after an anomaly. Sections
Section 3.1.2 and Section 5 of [RFC8404] provide further examples. 3.1.2 and 5 of [RFC8404] provide further examples.
Network segments vary in their complexity. The design trade-offs for Network segments vary in their complexity. The design trade-offs for
radio networks are often very different from those of wired networks radio networks are often very different from those of wired networks
[RFC8462]. A radio-based network (e.g., cellular mobile, enterprise [RFC8462]. A radio-based network (e.g., cellular mobile, enterprise
Wireless LAN (WLAN), satellite access/back-haul, point-to-point Wireless LAN (WLAN), satellite access/backhaul, point-to-point radio)
radio) adds a subsystem that performs radio resource management, with adds a subsystem that performs radio resource management, with impact
impact on the available capacity, and potentially loss/reordering of on the available capacity and potentially loss/reordering of packets.
packets. This impact can differ by traffic type, and can be This impact can differ by traffic type and can be correlated with
correlated with link propagation and interference. These can impact link propagation and interference. These can impact the cost and
the cost and performance of a provided service, and is expected to performance of a provided service and is expected to increase in
increase in importance as operators bring together heterogeneous importance as operators bring together heterogeneous types of network
types of network equipment and deploy opportunistic methods to access equipment and deploy opportunistic methods to access a shared radio
shared radio spectrum. spectrum.
2.4.7. Tooling and Network Operations 2.4.7. Tooling and Network Operations
A variety of open source and proprietary tools have been deployed A variety of open source and proprietary tools have been deployed
that use the transport header information observable with widely used that use the transport header information observable with widely used
protocols such as TCP or RTP/UDP/IP. Tools that dissect network protocols, such as TCP or RTP/UDP/IP. Tools that dissect network
traffic flows can alert to potential problems that are hard to derive traffic flows can alert to potential problems that are hard to derive
from volume measurements, link statistics or device measurements from volume measurements, link statistics, or device measurements
alone. alone.
Any introduction of a new transport protocol, protocol feature, or Any introduction of a new transport protocol, protocol feature, or
application might require changes to such tools, and so could impact application might require changes to such tools and could impact
operational practice and policies. Such changes have associated operational practice and policies. Such changes have associated
costs that are incurred by the network operators that need to update costs that are incurred by the network operators that need to update
their tooling or develop alternative practises that work without their tooling or develop alternative practises that work without
access to the changed/removed information. access to the changed/removed information.
The use of encryption has the desirable effect of preventing The use of encryption has the desirable effect of preventing
unintended observation of the payload data and these tools seldom unintended observation of the payload data, and these tools seldom
seek to observe the payload, or other application details. A flow seek to observe the payload or other application details. A flow
that hides its transport header information could imply "don't touch" that hides its transport header information could imply "don't touch"
to some operators. This might limit a trouble-shooting response to to some operators. This might limit a trouble-shooting response to
"can't help, no trouble found". "can't help, no trouble found".
An alternative that does not require access to observable transport An alternative that does not require access to an observable
headers is to access endpoint diagnostic tools or to include user transport headers is to access endpoint diagnostic tools or to
involvement in diagnosing and troubleshooting unusual use cases or to include user involvement in diagnosing and troubleshooting unusual
troubleshoot non-trivial problems. Another approach is to use use cases or to troubleshoot nontrivial problems. Another approach
traffic pattern analysis. Such tools can provide useful information is to use traffic pattern analysis. Such tools can provide useful
during network anomalies (e.g., detecting significant reordering, information during network anomalies (e.g., detecting significant
high or intermittent loss), however indirect measurements need to be reordering, high or intermittent loss); however, indirect
carefully designed to provide information for diagnostics and measurements need to be carefully designed to provide information for
troubleshooting. diagnostics and troubleshooting.
If new protocols, or protocol extensions, are made to closely If new protocols, or protocol extensions, are made to closely
resemble or match existing mechanisms, then the changes to tooling resemble or match existing mechanisms, then the changes to tooling
and the associated costs can be small. Equally, more extensive and the associated costs can be small. Equally, more extensive
changes to the transport tend to require more extensive, and more changes to the transport tend to require more extensive, and more
expensive, changes to tooling and operational practice. Protocol expensive, changes to tooling and operational practice. Protocol
designers can mitigate these costs by explicitly choosing to expose designers can mitigate these costs by explicitly choosing to expose
selected information as invariants that are guaranteed not to change selected information as invariants that are guaranteed not to change
for a particular protocol (e.g., the header invariants and the spin- for a particular protocol (e.g., the header invariants and the spin
bit in QUIC [I-D.ietf-quic-transport]). Specification of common log bit in QUIC [RFC9000]). Specification of common log formats and
formats and development of alternative approaches can also help development of alternative approaches can also help mitigate the
mitigate the costs of transport changes. costs of transport changes.
2.5. To Mitigate the Effects of Constrained Networks 2.5. To Mitigate the Effects of Constrained Networks
Some link and network segments are constrained by the capacity they Some link and network segments are constrained by the capacity they
can offer, by the time it takes to access capacity (e.g., due to can offer by the time it takes to access capacity (e.g., due to
under-lying radio resource management methods), or by asymmetries in underlying radio resource management methods) or by asymmetries in
the design (e.g., many link are designed so that the capacity the design (e.g., many link are designed so that the capacity
available is different in the forward and return directions; some available is different in the forward and return directions; some
radio technologies have different access methods in the forward and radio technologies have different access methods in the forward and
return directions resulting from differences in the power budget). return directions resulting from differences in the power budget).
The impact of path constraints can be mitigated using a proxy The impact of path constraints can be mitigated using a proxy
operating at or above the transport layer to use an alternate operating at or above the transport layer to use an alternate
transport protocol. transport protocol.
In many cases, one or both endpoints are unaware of the In many cases, one or both endpoints are unaware of the
characteristics of the constraining link or network segment and characteristics of the constraining link or network segment, and
mitigations are applied below the transport layer: Packet mitigations are applied below the transport layer. Packet
classification and QoS methods (described in various sections) can be classification and QoS methods (described in various sections) can be
beneficial in differentially prioritising certain traffic when there beneficial in differentially prioritising certain traffic when there
is a capacity constraint or additional delay in scheduling link is a capacity constraint or additional delay in scheduling link
transmissions. Another common mitigation is to apply header transmissions. Another common mitigation is to apply header
compression over the specific link or subnetwork (see Section 2.5.1). compression over the specific link or subnetwork (see Section 2.5.1).
2.5.1. To Provide Header Compression 2.5.1. To Provide Header Compression
Header compression saves link capacity by compressing network and Header compression saves link capacity by compressing network and
transport protocol headers on a per-hop basis. This has been widely transport protocol headers on a per-hop basis. This has been widely
used with low bandwidth dial-up access links, and still finds used with low bandwidth dial-up access links and still finds
application on wireless links that are subject to capacity application on wireless links that are subject to capacity
constraints. These methods are effective for bit-congestive links constraints. These methods are effective for bit-congestive links
sending small packets (e.g., reducing the cost for sending control sending small packets (e.g., reducing the cost for sending control
packets or small data packets over radio links). packets or small data packets over radio links).
Examples of header compression include use with TCP/IP and RTP/UDP/IP Examples of header compression include use with TCP/IP and RTP/UDP/IP
flows [RFC2507], [RFC6846], [RFC2508], [RFC5795], [RFC8724]. flows [RFC2507] [RFC6846] [RFC2508] [RFC5795] [RFC8724]. Successful
Successful compression depends on observing the transport headers and compression depends on observing the transport headers and
understanding of the way fields change between packets, and is hence understanding the way fields change between packets and is hence
incompatible with header encryption. Devices that compress transport incompatible with header encryption. Devices that compress transport
headers are dependent on a stable header format, implying headers are dependent on a stable header format, implying
ossification of that format. ossification of that format.
Introducing a new transport protocol, or changing the format of the Introducing a new transport protocol, or changing the format of the
transport header information, will limit the effectiveness of header transport header information, will limit the effectiveness of header
compression until the network devices are updated. Encrypting the compression until the network devices are updated. Encrypting the
transport protocol headers will tend to cause the header compression transport protocol headers will tend to cause the header compression
to fall back to compressing only the network layer headers, with a to fall back to compressing only the network-layer headers, with a
significant reduction in efficiency. This can limit connectivity if significant reduction in efficiency. This can limit connectivity if
the resulting flow exceeds the link capacity, or if the packets are the resulting flow exceeds the link capacity or if the packets are
dropped because they exceed the link MTU. dropped because they exceed the link Maximum Transmission Unit (MTU).
The Secure RTP (SRTP) extensions [RFC3711] were explicitly designed The Secure RTP (SRTP) extensions [RFC3711] were explicitly designed
to leave the transport protocol headers unencrypted, but to leave the transport protocol headers unencrypted, but
authenticated, since support for header compression was considered authenticated, since support for header compression was considered
important. important.
2.6. To Verify SLA Compliance 2.6. To Verify SLA Compliance
Observable transport headers coupled with published transport Observable transport headers coupled with published transport
specifications allow operators and regulators to explore and verify specifications allow operators and regulators to explore and verify
compliance with Service Level Agreements (SLAs). It can also be used compliance with Service Level Agreements (SLAs). It can also be used
to understand whether a service is providing differential treatment to understand whether a service is providing differential treatment
to certain flows. to certain flows.
When transport header information cannot be observed, other methods When transport header information cannot be observed, other methods
have to be found to confirm that the traffic produced conforms to the have to be found to confirm that the traffic produced conforms to the
expectations of the operator or developer. expectations of the operator or developer.
Independently verifiable performance metrics can be utilised to Independently verifiable performance metrics can be utilised to
demonstrate regulatory compliance in some jurisdictions, and as a demonstrate regulatory compliance in some jurisdictions and as a
basis for informing design decisions. This can bring assurance to basis for informing design decisions. This can bring assurance to
those operating networks, often avoiding deployment of complex those operating networks, often avoiding deployment of complex
techniques that routinely monitor and manage Internet traffic flows techniques that routinely monitor and manage Internet traffic flows
(e.g., avoiding the capital and operational costs of deploying flow (e.g., avoiding the capital and operational costs of deploying flow
rate-limiting and network circuit-breaker methods [RFC8084]). rate-limiting and network circuit breaker methods [RFC8084]).
3. Research, Development and Deployment 3. Research, Development, and Deployment
Research and development of new protocols and mechanisms need to be Research and development of new protocols and mechanisms need to be
informed by measurement data (as described in the previous section). informed by measurement data (as described in the previous section).
Data can also help promote acceptance of proposed standards Data can also help promote acceptance of proposed standards
specifications by the wider community (e.g., as a method to judge the specifications by the wider community (e.g., as a method to judge the
safety for Internet deployment). safety for Internet deployment).
Observed data is important to ensure the health of the research and Observed data is important to ensure the health of the research and
development communities, and provides data needed to evaluate new development communities and provides data needed to evaluate new
proposals for standardisation. Open standards motivate a desire to proposals for standardisation. Open standards motivate a desire to
include independent observation and evaluation of performance and include independent observation and evaluation of performance and
deployment data. Independent data helps compare different methods, deployment data. Independent data helps compare different methods,
judge the level of deployment and ensure the wider applicability of judge the level of deployment, and ensure the wider applicability of
the results. This is important when considering when a protocol or the results. This is important when considering when a protocol or
mechanism should be standardised for use in the general Internet. mechanism should be standardised for use in the general Internet.
This, in turn, demands control/understanding about where and when This, in turn, demands control/understanding about where and when
measurement samples are collected. This requires consideration of measurement samples are collected. This requires consideration of
the methods used to observe information and the appropriate balance the methods used to observe information and the appropriate balance
between encrypting all and no transport header information. between encrypting all and no transport header information.
There can be performance and operational trade-offs in exposing There can be performance and operational trade-offs in exposing
selected information to network tools. This section explores key selected information to network tools. This section explores key
implications of tools and procedures that observe transport implications of tools and procedures that observe transport protocols
protocols, but does not endorse or condemn any specific practises. but does not endorse or condemn any specific practises.
3.1. Independent Measurement 3.1. Independent Measurement
Encrypting transport header information has implications on the way Encrypting transport header information has implications on the way
network data is collected and analysed. Independent observation by network data is collected and analysed. Independent observations by
multiple actors is currently used by the transport community to multiple actors is currently used by the transport community to
maintain an accurate understanding of the network within transport maintain an accurate understanding of the network within transport
area working groups, IRTF research groups, and the broader research area working groups, IRTF research groups, and the broader research
community. This is important to be able to provide accountability, community. This is important to be able to provide accountability
and demonstrate that protocols behave as intended, although when and demonstrate that protocols behave as intended; although, when
providing or using such information, it is important to consider the providing or using such information, it is important to consider the
privacy of the user and their incentive for providing accurate and privacy of the user and their incentive for providing accurate and
detailed information. detailed information.
Protocols that expose the state of the transport protocol in their Protocols that expose the state of the transport protocol in their
header (e.g., timestamps used to calculate the RTT, packet numbers header (e.g., timestamps used to calculate the RTT, packet numbers
used to assess congestion and requests for retransmission) provide an used to assess congestion, and requests for retransmission) provide
incentive for a sending endpoint to provide consistent information, an incentive for a sending endpoint to provide consistent
because a protocol will not work otherwise. An on-path observer can information, because a protocol will not work otherwise. An on-path
have confidence that well-known (and ossified) transport header observer can have confidence that well-known (and ossified) transport
information represents the actual state of the endpoints, when this header information represents the actual state of the endpoints when
information is necessary for the protocol's correct operation. this information is necessary for the protocol's correct operation.
Encryption of transport header information could reduce the range of Encryption of transport header information could reduce the range of
actors that can observe useful data. This would limit the actors that can observe useful data. This would limit the
information sources available to the Internet community to understand information sources available to the Internet community to understand
the operation of new transport protocols, reducing information to the operation of new transport protocols, reducing information to
inform design decisions and standardisation of the new protocols and inform design decisions and standardisation of the new protocols and
related operational practises. The cooperating dependence of related operational practises. The cooperating dependence of
network, application, and host to provide communication performance network, application, and host to provide communication performance
on the Internet is uncertain when only endpoints (i.e., at user on the Internet is uncertain when only endpoints (i.e., at user
devices and within service platforms) can observe performance, and devices and within service platforms) can observe performance and
when performance cannot be independently verified by all parties. when performance cannot be independently verified by all parties.
3.2. Measurable Transport Protocols 3.2. Measurable Transport Protocols
Transport protocol evolution, and the ability to measure and Transport protocol evolution and the ability to measure and
understand the impact of protocol changes, have to proceed hand-in- understand the impact of protocol changes have to proceed hand-in-
hand. A transport protocol that provides observable headers can be hand. A transport protocol that provides observable headers can be
used to provide open and verifiable measurement data. Observation of used to provide open and verifiable measurement data. Observation of
pathologies has a critical role in the design of transport protocol pathologies has a critical role in the design of transport protocol
mechanisms and development of new mechanisms and protocols, and aides mechanisms and development of new mechanisms and protocols and aides
understanding of the interactions between cooperating protocols and in understanding the interactions between cooperating protocols and
network mechanisms, the implications of sharing capacity with other network mechanisms, the implications of sharing capacity with other
traffic and the impact of different patterns of usage. The ability traffic, and the impact of different patterns of usage. The ability
of other stakeholders to review transport header traces helps develop of other stakeholders to review transport header traces helps develop
insight into the performance and the traffic contribution of specific insight into the performance and the traffic contribution of specific
variants of a protocol. variants of a protocol.
Development of new transport protocol mechanisms has to consider the Development of new transport protocol mechanisms has to consider the
scale of deployment and the range of environments in which the scale of deployment and the range of environments in which the
transport is used. Experience has shown that it is often difficult transport is used. Experience has shown that it is often difficult
to correctly implement new mechanisms [RFC8085], and that mechanisms to correctly implement new mechanisms [RFC8085] and that mechanisms
often evolve as a protocol matures, or in response to changes in often evolve as a protocol matures or in response to changes in
network conditions, changes in network traffic, or changes to network conditions, in network traffic, or to application usage.
application usage. Analysis is especially valuable when based on the Analysis is especially valuable when based on the behaviour
behaviour experienced across a range of topologies, vendor equipment, experienced across a range of topologies, vendor equipment, and
and traffic patterns. traffic patterns.
Encryption enables a transport protocol to choose which internal Encryption enables a transport protocol to choose which internal
state to reveal to devices on the network path, what information to state to reveal to devices on the network path, what information to
encrypt, and what fields to grease [RFC8701]. A new design can encrypt, and what fields to grease [RFC8701]. A new design can
provide summary information regarding its performance, congestion provide summary information regarding its performance, congestion
control state, etc., or to make available explicit measurement control state, etc., or make explicit measurement information
information. For example, [I-D.ietf-quic-transport] specifies a way available. For example, [RFC9000] specifies a way for a QUIC
for a QUIC endpoint to optionally set the spin-bit to explicitly endpoint to optionally set the spin bit to explicitly reveal the RTT
reveal the RTT of an encrypted transport session to the on-path of an encrypted transport session to the on-path network devices.
network devices. There is a choice of what information to expose. There is a choice of what information to expose. For some
For some operational uses, the information has to contain sufficient operational uses, the information has to contain sufficient detail to
detail to understand, and possibly reconstruct, the network traffic understand, and possibly reconstruct, the network traffic pattern for
pattern for further testing. The interpretation of the information further testing. The interpretation of the information needs to
needs to consider whether this information reflects the actual consider whether this information reflects the actual transport state
transport state of the endpoints. This might require the trust of of the endpoints. This might require the trust of transport protocol
transport protocol implementers, to correctly reveal the desired implementers to correctly reveal the desired information.
information.
New transport protocol formats are expected to facilitate an New transport protocol formats are expected to facilitate an
increased pace of transport evolution, and with it the possibility to increased pace of transport evolution and with it the possibility to
experiment with and deploy a wide range of protocol mechanisms. At experiment with and deploy a wide range of protocol mechanisms. At
the time of writing, there has been interest in a wide range of new the time of writing, there has been interest in a wide range of new
transport methods, e.g., Larger Initial Window, Proportional Rate transport methods, e.g., larger initial window, Proportional Rate
Reduction (PRR), congestion control methods based on measuring Reduction (PRR), congestion control methods based on measuring
bottleneck bandwidth and round-trip propagation time, the bottleneck bandwidth and round-trip propagation time, the
introduction of AQM techniques and new forms of ECN response (e.g., introduction of AQM techniques, and new forms of ECN response (e.g.,
Data Centre TCP, DCTCP, and methods proposed for L4S). The growth Data Centre TCP, DCTCP, and methods proposed for Low Latency Low Loss
and diversity of applications and protocols using the Internet also Scalable throughput (L4S)). The growth and diversity of applications
continues to expand. For each new method or application, it is and protocols using the Internet also continues to expand. For each
desirable to build a body of data reflecting its behaviour under a new method or application, it is desirable to build a body of data
wide range of deployment scenarios, traffic load, and interactions reflecting its behaviour under a wide range of deployment scenarios,
with other deployed/candidate methods. traffic load, and interactions with other deployed/candidate methods.
3.3. Other Sources of Information 3.3. Other Sources of Information
Some measurements that traditionally rely on observable transport Some measurements that traditionally rely on observable transport
information could be completed by utilising endpoint-based logging information could be completed by utilising endpoint-based logging
(e.g., based on Quic-Trace [Quic-Trace] and qlog (e.g., based on QUIC trace [Quic-Trace] and qlog [QLOG]). Such
[I-D.marx-qlog-main-schema]). Such information has a diversity of information has a diversity of uses, including developers wishing to
uses, including developers wishing to debug/understand the transport/ debug/understand the transport/application protocols with which they
application protocols with which they work, researchers seeking to work, researchers seeking to spot trends and anomalies, and to
spot trends and anomalies, and to characterise variants of protocols. characterise variants of protocols. A standard format for endpoint
A standard format for endpoint logging could allow these to be shared logging could allow these to be shared (after appropriate
(after appropriate anonymisation) to understand performance and anonymisation) to understand performance and pathologies.
pathologies.
When measurement datasets are made available by servers or client When measurement datasets are made available by servers or client
endpoints, additional metadata, such as the state of the network and endpoints, additional metadata, such as the state of the network and
conditions in which the system was observed, is often necessary to conditions in which the system was observed, is often necessary to
interpret this data to answer questions about network performance or interpret this data to answer questions about network performance or
understand a pathology. Collecting and coordinating such metadata is understand a pathology. Collecting and coordinating such metadata is
more difficult when the observation point is at a different location more difficult when the observation point is at a different location
to the bottleneck or device under evaluation [RFC7799]. to the bottleneck or device under evaluation [RFC7799].
Despite being applicable in some scenarios, endpoint logs do not Despite being applicable in some scenarios, endpoint logs do not
provide equivalent information to on-path measurements made by provide equivalent information to on-path measurements made by
devices in the network. In particular, endpoint logs contain only a devices in the network. In particular, endpoint logs contain only a
part of the information to understand the operation of network part of the information to understand the operation of network
devices and identify issues such as link performance or capacity devices and identify issues, such as link performance or capacity
sharing between multiple flows. An analysis can require coordination sharing between multiple flows. An analysis can require coordination
between actors at different layers to successfully characterise flows between actors at different layers to successfully characterise flows
and correlate the performance or behaviour of a specific mechanism and correlate the performance or behaviour of a specific mechanism
with an equipment configuration and traffic using operational with an equipment configuration and traffic using operational
equipment along a network path (e.g., combining transport and network equipment along a network path (e.g., combining transport and network
measurements to explore congestion control dynamics, to understand measurements to explore congestion control dynamics to understand the
the implications of traffic on designs for active queue management or implications of traffic on designs for active queue management or
circuit breakers). circuit breakers).
Another source of information could arise from operations, Another source of information could arise from Operations,
administration and management (OAM) (see Section 6) information data Administration, and Maintenance (OAM) (see Section 6). Information
records could be embedded into header information at different layers data records could be embedded into header information at different
to support functions such as performance evaluation, path-tracing, layers to support functions, such as performance evaluation, path
path verification information, classification and a diversity of tracing, path verification information, classification, and a
other uses. diversity of other uses.
In-situ OAM (IOAM) data fields [I-D.ietf-ippm-ioam-data] can be In-situ OAM (IOAM) data fields [IOAM-DATA] can be encapsulated into a
encapsulated into a variety of protocols to record operational and variety of protocols to record operational and telemetry information
telemetry information in an existing packet, while that packet in an existing packet while that packet traverses a part of the path
traverses a part of the path between two points in a network (e.g., between two points in a network (e.g., within a particular IOAM
within a particular IOAM management domain). The IOAM-Data-Fields management domain). IOAM-Data-Fields are independent from the
are independent from the protocols into which the IOAM-Data-Fields protocols into which IOAM-Data-Fields are encapsulated. For example,
are encapsulated. For example, IOAM can provide proof that a certain IOAM can provide proof that a traffic flow takes a predefined path,
traffic flow takes a pre-defined path, SLA verification for the live SLA verification for the live data traffic, and statistics relating
data traffic, and statistics relating to traffic distribution. to traffic distribution.
4. Encryption and Authentication of Transport Headers 4. Encryption and Authentication of Transport Headers
There are several motivations for transport header encryption. There are several motivations for transport header encryption.
One motive to encrypt transport headers is to prevent network One motive to encrypt transport headers is to prevent network
ossification from network devices that inspect well-known transport ossification from network devices that inspect well-known transport
headers. Once a network device observes a transport header and headers. Once a network device observes a transport header and
becomes reliant upon using it, the overall use of that field can becomes reliant upon using it, the overall use of that field can
become ossified, preventing new versions of the protocol and become ossified, preventing new versions of the protocol and
mechanisms from being deployed. Examples include: mechanisms from being deployed. Examples include:
o During the development of TLS 1.3 [RFC8446], the design needed to * During the development of TLS 1.3 [RFC8446], the design needed to
function in the presence of deployed middleboxes that relied on function in the presence of deployed middleboxes that relied on
the presence of certain header fields exposed in TLS 1.2 the presence of certain header fields exposed in TLS 1.2
[RFC5426]. [RFC5426].
o The design of Multipath TCP (MPTCP) [RFC8684] had to account for * The design of Multipath TCP (MPTCP) [RFC8684] had to account for
middleboxes (known as "TCP Normalizers") that monitor the middleboxes (known as "TCP Normalizers") that monitor the
evolution of the window advertised in the TCP header and then evolution of the window advertised in the TCP header and then
reset connections when the window did not grow as expected. reset connections when the window did not grow as expected.
o TCP Fast Open [RFC7413] can experience problems due to middleboxes * TCP Fast Open [RFC7413] can experience problems due to middleboxes
that modify the transport header of packets by removing "unknown" that modify the transport header of packets by removing "unknown"
TCP options. Segments with unrecognised TCP options can be TCP options. Segments with unrecognised TCP options can be
dropped, segments that contain data and set the SYN bit can be dropped, segments that contain data and set the SYN bit can be
dropped, and some middleboxes that disrupt connections that send dropped, and some middleboxes that disrupt connections can send
data before completion of the three-way handshake. data before completion of the three-way handshake.
o Other examples of TCP ossification have included middleboxes that * Other examples of TCP ossification have included middleboxes that
modify transport headers by rewriting TCP sequence and modify transport headers by rewriting TCP sequence and
acknowledgement numbers, but are unaware of the (newer) TCP acknowledgement numbers but are unaware of the (newer) TCP
selective acknowledgement (SACK) option and therefore fail to selective acknowledgement (SACK) option and therefore fail to
correctly rewrite the SACK information to match the changes made correctly rewrite the SACK information to match the changes made
to the fixed TCP header, preventing correct SACK operation. to the fixed TCP header, preventing correct SACK operation.
In all these cases, middleboxes with a hard-coded, but incomplete, In all these cases, middleboxes with a hard-coded, but incomplete,
understanding of a specific transport behaviour (i.e., TCP), understanding of a specific transport behaviour (i.e., TCP)
interacted poorly with transport protocols after the transport interacted poorly with transport protocols after the transport
behaviour was changed. In some cases, the middleboxes modified or behaviour was changed. In some cases, the middleboxes modified or
replaced information in the transport protocol header. replaced information in the transport protocol header.
Transport header encryption prevents an on-path device from observing Transport header encryption prevents an on-path device from observing
the transport headers, and therefore stops ossified mechanisms being the transport headers and therefore stops ossified mechanisms being
used that directly rely on or infer semantics of the transport header used that directly rely on or infer semantics of the transport header
information. This encryption is normally combined with information. This encryption is normally combined with
authentication of the protected information. RFC 8546 summarises authentication of the protected information. [RFC8546] summarises
this approach, stating that it is "The wire image, not the protocol's this approach, stating that "[t]he wire image, not the protocol's
specification, determines how third parties on the network paths specification, determines how third parties on the network paths
among protocol participants will interact with that protocol" among protocol participants will interact with that protocol"
(Section 1 of [RFC8546]), and it can be expected that header (Section 1 of [RFC8546]), and it can be expected that header
information that is not encrypted will become ossified. information that is not encrypted will become ossified.
Encryption does not itself prevent ossification of the network Encryption does not itself prevent ossification of the network
service. People seeking to understand or classify network traffic service. People seeking to understand or classify network traffic
could still come to rely on pattern inferences and other heuristics could still come to rely on pattern inferences and other heuristics
or machine learning to derive measurement data and as the basis for or machine learning to derive measurement data and as the basis for
network forwarding decisions [RFC8546]. This can also create network forwarding decisions [RFC8546]. This can also create
dependencies on the transport protocol, or the patterns of traffic it dependencies on the transport protocol or the patterns of traffic it
can generate, also resulting in ossification of the service. can generate, also resulting in ossification of the service.
Another motivation for using transport header encryption is to Another motivation for using transport header encryption is to
improve privacy and to decrease opportunities for surveillance. improve privacy and to decrease opportunities for surveillance.
Users value the ability to protect their identity and location, and Users value the ability to protect their identity and location and
defend against analysis of the traffic. Revelations about the use of defend against analysis of the traffic. Revelations about the use of
pervasive surveillance [RFC7624] have, to some extent, eroded trust pervasive surveillance [RFC7624] have, to some extent, eroded trust
in the service offered by network operators and have led to an in the service offered by network operators and have led to an
increased use of encryption. Concerns have also been voiced about increased use of encryption. Concerns have also been voiced about
the addition of metadata to packets by third parties to provide the addition of metadata to packets by third parties to provide
analytics, customisation, advertising, cross-site tracking of users, analytics, customisation, advertising, cross-site tracking of users,
to bill the customer, or to selectively allow or block content. customer billing, or selectively allowing or blocking content.
Whatever the reasons, the IETF is designing protocols that include Whatever the reasons, the IETF is designing protocols that include
transport header encryption (e.g., QUIC [I-D.ietf-quic-transport]) to transport header encryption (e.g., QUIC [RFC9000]) to supplement the
supplement the already widespread payload encryption, and to further already widespread payload encryption and to further limit exposure
limit exposure of transport metadata to the network. of transport metadata to the network.
If a transport protocol uses header encryption, the designers have to If a transport protocol uses header encryption, the designers have to
decide whether to encrypt all, or a part of, the transport layer decide whether to encrypt all or a part of the transport-layer
information. Section 4 of [RFC8558] states: "Anything exposed to the information. Section 4 of [RFC8558] states, "Anything exposed to the
path should be done with the intent that it be used by the network path should be done with the intent that it be used by the network
elements on the path". elements on the path."
Certain transport header fields can be made observable to on-path Certain transport header fields can be made observable to on-path
network devices, or can define new fields designed to explicitly network devices or can define new fields designed to explicitly
expose observable transport layer information to the network. Where expose observable transport-layer information to the network. Where
exposed fields are intended to be immutable (i.e., can be observed, exposed fields are intended to be immutable (i.e., can be observed
but not modified by a network device), the endpoints are encouraged but not modified by a network device), the endpoints are encouraged
to use authentication to provide a cryptographic integrity check that to use authentication to provide a cryptographic integrity check that
can detect if these immutable fields have been modified by network can detect if these immutable fields have been modified by network
devices. Authentication can help to prevent attacks that rely on devices. Authentication can help to prevent attacks that rely on
sending packets that fake exposed control signals in transport sending packets that fake exposed control signals in transport
headers (e.g., TCP RST spoofing). Making a part of a transport headers (e.g., TCP RST spoofing). Making a part of a transport
header observable or exposing new header fields can lead to header observable or exposing new header fields can lead to
ossification of that part of a header as network devices come to rely ossification of that part of a header as network devices come to rely
on observations of the exposed fields. on observations of the exposed fields.
The use of transport header authentication and encryption therefore The use of transport header authentication and encryption therefore
exposes a tussle between middlebox vendors, operators, researchers, exposes a tussle between middlebox vendors, operators, researchers,
applications developers, and end-users: applications developers, and end users:
o On the one hand, future Internet protocols that support transport * On the one hand, future Internet protocols that support transport
header encryption assist in the restoration of the end-to-end header encryption assist in the restoration of the end-to-end
nature of the Internet by returning complex processing to the nature of the Internet by returning complex processing to the
endpoints. Since middleboxes cannot modify what they cannot see, endpoints. Since middleboxes cannot modify what they cannot see,
the use of transport header encryption can improve application and the use of transport header encryption can improve application and
end-user privacy by reducing leakage of transport metadata to end-user privacy by reducing leakage of transport metadata to
operators that deploy middleboxes. operators that deploy middleboxes.
o On the other hand, encryption of transport layer information has * On the other hand, encryption of transport-layer information has
implications for network operators and researchers seeking to implications for network operators and researchers seeking to
understand the dynamics of protocols and traffic patterns, since understand the dynamics of protocols and traffic patterns, since
it reduces the information that is available to them. it reduces the information that is available to them.
The following briefly reviews some security design options for The following briefly reviews some security design options for
transport protocols. A Survey of the Interaction between Security transport protocols. "A Survey of the Interaction between Security
Protocols and Transport Services [RFC8922] provides more details Protocols and Transport Services" [RFC8922] provides more details
concerning commonly used encryption methods at the transport layer. concerning commonly used encryption methods at the transport layer.
Security work typically employs a design technique that seeks to Security work typically employs a design technique that seeks to
expose only what is needed [RFC3552]. This approach provides expose only what is needed [RFC3552]. This approach provides
incentives to not reveal any information that is not necessary for incentives to not reveal any information that is not necessary for
the end-to-end communication. The IETF has provided guidelines for the end-to-end communication. The IETF has provided guidelines for
writing Security Considerations for IETF specifications [RFC3552]. writing security considerations for IETF specifications [RFC3552].
Endpoint design choices impacting privacy also need to be considered Endpoint design choices impacting privacy also need to be considered
as a part of the design process [RFC6973]. The IAB has provided as a part of the design process [RFC6973]. The IAB has provided
guidance for analyzing and documenting privacy considerations within guidance for analysing and documenting privacy considerations within
IETF specifications [RFC6973]. IETF specifications [RFC6973].
Authenticating the Transport Protocol Header: Transport layer header Authenticating the Transport Protocol Header:
information can be authenticated. An example transport Transport-layer header information can be authenticated. An
authentication mechanism is TCP-Authentication (TCP-AO) [RFC5925]. example transport authentication mechanism is TCP Authentication
This TCP option authenticates the IP pseudo header, TCP header, Option (TCP-AO) [RFC5925]. This TCP option authenticates the IP
and TCP data. TCP-AO protects the transport layer, preventing pseudo-header, TCP header, and TCP data. TCP-AO protects the
attacks from disabling the TCP connection itself and provides transport layer, preventing attacks from disabling the TCP
replay protection. Such authentication might interact with connection itself and provides replay protection. Such
middleboxes, depending on their behaviour [RFC3234]. authentication might interact with middleboxes, depending on their
behaviour [RFC3234].
The IPsec Authentication Header (AH) [RFC4302] was designed to The IPsec Authentication Header (AH) [RFC4302] was designed to
work at the network layer and authenticate the IP payload. This work at the network layer and authenticate the IP payload. This
approach authenticates all transport headers, and verifies their approach authenticates all transport headers and verifies their
integrity at the receiver, preventing modification by network integrity at the receiver, preventing modification by network
devices on the path. The IPsec Encapsulating Security Payload devices on the path. The IPsec Encapsulating Security Payload
(ESP) [RFC4303] can also provide authentication and integrity (ESP) [RFC4303] can also provide authentication and integrity
without confidentiality using the NULL encryption algorithm without confidentiality using the NULL encryption algorithm
[RFC2410]. SRTP [RFC3711] is another example of a transport [RFC2410]. SRTP [RFC3711] is another example of a transport
protocol that allows header authentication. protocol that allows header authentication.
Integrity Check Transport protocols usually employ integrity checks Integrity Check:
on the transport header information. Security method usually Transport protocols usually employ integrity checks on the
employ stronger checks and can combine this with authentication. transport header information. Security methods usually employ
An integrity check that protects the immutable transport header stronger checks and can combine this with authentication. An
integrity check that protects the immutable transport header
fields, but can still expose the transport header information in fields, but can still expose the transport header information in
the clear, allows on-path network devices to observe these fields. the clear, allows on-path network devices to observe these fields.
An integrity check is not able to prevent modification by network An integrity check is not able to prevent modification by network
devices on the path, but can prevent a receiving endpoint from devices on the path but can prevent a receiving endpoint from
accepting changes and avoid impact on the transport protocol accepting changes and avoid impact on the transport protocol
operation, including some types of attack. operation, including some types of attack.
Selectively Encrypting Transport Headers and Payload: A transport Selectively Encrypting Transport Headers and Payload:
protocol design that encrypts selected header fields, allows A transport protocol design that encrypts selected header fields
specific transport header fields to be made observable by network allows specific transport header fields to be made observable by
devices on the path. This information is explicitly exposed network devices on the path. This information is explicitly
either in a transport header field or lower layer protocol header. exposed either in a transport header field or lower layer protocol
A design that only exposes immutable fields can also perform end- header. A design that only exposes immutable fields can also
to-end authentication of these fields across the path to prevent perform end-to-end authentication of these fields across the path
undetected modification of the immutable transport headers. to prevent undetected modification of the immutable transport
headers.
Mutable fields in the transport header provide opportunities where Mutable fields in the transport header provide opportunities where
on-path network devices can modify the transport behaviour (e.g., on-path network devices can modify the transport behaviour (e.g.,
the extended headers described in the extended headers described in [PLUS-ABSTRACT-MECH]). An
[I-D.trammell-plus-abstract-mech]). An example of a method that example of a method that encrypts some, but not all, transport
encrypts some, but not all, transport header information is GRE- header information is GRE-in-UDP [RFC8086] when used with GRE
in-UDP [RFC8086] when used with GRE encryption. encryption.
Optional Encryption of Header Information: There are implications to Optional Encryption of Header Information:
the use of optional header encryption in the design of a transport There are implications to the use of optional header encryption in
protocol, where support of optional mechanisms can increase the the design of a transport protocol, where support of optional
complexity of the protocol and its implementation, and in the mechanisms can increase the complexity of the protocol and its
management decisions that have to be made to use variable format implementation and in the management decisions that have to be
fields. Instead, fields of a specific type ought to be sent with made to use variable format fields. Instead, fields of a specific
the same level of confidentiality or integrity protection. type ought to be sent with the same level of confidentiality or
integrity protection.
Greasing: Protocols often provide extensibility features, reserving Greasing:
fields or values for use by future versions of a specification. Protocols often provide extensibility features, reserving fields
The specification of receivers has traditionally ignored or values for use by future versions of a specification. The
unspecified values, however on-path network devices have emerged specification of receivers has traditionally ignored unspecified
that ossify to require a certain value in a field, or re-use a values; however, on-path network devices have emerged that ossify
field for another purpose. When the specification is later to require a certain value in a field or reuse a field for another
updated, it is impossible to deploy the new use of the field, and purpose. When the specification is later updated, it is
forwarding of the protocol could even become conditional on a impossible to deploy the new use of the field and forwarding of
specific header field value. the protocol could even become conditional on a specific header
field value.
A protocol can intentionally vary the value, format, and/or A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields at random presence of observable transport header fields at random
[RFC8701]. This prevents a network device ossifying the use of a [RFC8701]. This prevents a network device ossifying the use of a
specific observable field and can ease future deployment of new specific observable field and can ease future deployment of new
uses of the value or code-point. This is not a security uses of the value or code point. This is not a security
mechanism, although the use can be combined with an authentication mechanism, although the use can be combined with an authentication
mechanism. mechanism.
Different transports use encryption to protect their header Different transports use encryption to protect their header
information to varying degrees. The trend is towards increased information to varying degrees. The trend is towards increased
protection. protection.
5. Intentionally Exposing Transport Information to the Network 5. Intentionally Exposing Transport Information to the Network
A transport protocol can choose to expose certain transport A transport protocol can choose to expose certain transport
skipping to change at page 28, line 22 skipping to change at line 1313
Another approach is to expose transport information in a network- Another approach is to expose transport information in a network-
layer extension header (see Section 5.1). Both are examples of layer extension header (see Section 5.1). Both are examples of
explicit information intended to be used by network devices on the explicit information intended to be used by network devices on the
path [RFC8558]. path [RFC8558].
Whatever the mechanism used to expose the information, a decision to Whatever the mechanism used to expose the information, a decision to
expose only specific information places the transport endpoint in expose only specific information places the transport endpoint in
control of what to expose outside of the encrypted transport header. control of what to expose outside of the encrypted transport header.
This decision can then be made independently of the transport This decision can then be made independently of the transport
protocol functionality. This can be done by exposing part of the protocol functionality. This can be done by exposing part of the
transport header or as a network layer option/extension. transport header or as a network-layer option/extension.
5.1. Exposing Transport Information in Extension Headers 5.1. Exposing Transport Information in Extension Headers
At the network-layer, packets can carry optional headers that At the network layer, packets can carry optional headers that
explicitly expose transport header information to the on-path devices explicitly expose transport header information to the on-path devices
operating at the network layer (Section 2.3.2). For example, an operating at the network layer (Section 2.3.2). For example, an
endpoint that sends an IPv6 Hop-by-Hop option [RFC8200] can provide endpoint that sends an IPv6 hop-by-hop option [RFC8200] can provide
explicit transport layer information that can be observed and used by explicit transport-layer information that can be observed and used by
network devices on the path. New hop-by-hop options are not network devices on the path. New hop-by-hop options are not
recommended in RFC 8200 [RFC8200] "because nodes may be configured to recommended in [RFC8200] "because nodes may be configured to ignore
ignore the Hop-by-Hop Options header, drop packets containing a Hop- the Hop-by-Hop Options header, drop packets containing a Hop-by-Hop
by-Hop Options header, or assign packets containing a Hop-by-Hop Options header, or assign packets containing a Hop-by-Hop Options
Options header to a slow processing path. Designers considering header to a slow processing path. Designers considering defining new
defining new hop-by-hop options need to be aware of this likely hop-by-hop options need to be aware of this likely behavior."
behavior."
Network-layer optional headers explicitly indicate the information Network-layer optional headers explicitly indicate the information
that is exposed, whereas use of exposed transport header information that is exposed, whereas use of exposed transport header information
first requires an observer to identify the transport protocol and its first requires an observer to identify the transport protocol and its
format. (See Section 2.2.) format. See Section 2.2.
An arbitrary path can include one or more network devices that drop An arbitrary path can include one or more network devices that drop
packets that include a specific header or option used for this packets that include a specific header or option used for this
purpose (see [RFC7872]). This could impact the proper functioning of purpose (see [RFC7872]). This could impact the proper functioning of
the protocols using the path. Protocol methods can be designed to the protocols using the path. Protocol methods can be designed to
probe to discover whether the specific option(s) can be used along probe to discover whether the specific option(s) can be used along
the current path, enabling use on arbitrary paths. the current path, enabling use on arbitrary paths.
5.2. Common Exposed Transport Information 5.2. Common Exposed Transport Information
skipping to change at page 29, line 18 skipping to change at line 1354
consistently supply common observable information [RFC8558]. A consistently supply common observable information [RFC8558]. A
common approach can result in an open definition of the observable common approach can result in an open definition of the observable
fields. This has the potential that the same information can be fields. This has the potential that the same information can be
utilised across a range of operational and analysis tools. utilised across a range of operational and analysis tools.
5.3. Considerations for Exposing Transport Information 5.3. Considerations for Exposing Transport Information
Considerations concerning what information, if any, it is appropriate Considerations concerning what information, if any, it is appropriate
to expose include: to expose include:
o On the one hand, explicitly exposing derived fields containing * On the one hand, explicitly exposing derived fields containing
relevant transport information (e.g., metrics for loss, latency, relevant transport information (e.g., metrics for loss, latency,
etc) can avoid network devices needing to derive this information etc.) can avoid network devices needing to derive this information
from other header fields. This could result in development and from other header fields. This could result in development and
evolution of transport-independent tools around a common evolution of transport-independent tools around a common
observable header, and permit transport protocols to also evolve observable header and permit transport protocols to also evolve
independently of this ossified header [RFC8558]. independently of this ossified header [RFC8558].
o On the other hand, protocols and implementations might be designed * On the other hand, protocols and implementations might be designed
to avoid consistently exposing external information that to avoid consistently exposing external information that
corresponds to the actual internal information used by the corresponds to the actual internal information used by the
protocol itself. An endpoint/protocol could choose to expose protocol itself. An endpoint/protocol could choose to expose
transport header information to optimise the benefit it gets from transport header information to optimise the benefit it gets from
the network [RFC8558]. The value of this information for the network [RFC8558]. The value of this information for
analysing operation of the transport layer would be enhanced if analysing operation of the transport layer would be enhanced if
the exposed information could be verified to match the transport the exposed information could be verified to match the transport
protocol's observed behavior. protocol's observed behavior.
The motivation to include actual transport header information and the The motivation to include actual transport header information and the
implications of network devices using this information has to be implications of network devices using this information has to be
considered when proposing such a method. RFC 8558 summarises this as considered when proposing such a method. [RFC8558] summarises this
"When signals from endpoints to the path are independent from the as:
signals used by endpoints to manage the flow's state mechanics, they
may be falsified by an endpoint without affecting the peer's | When signals from endpoints to the path are independent from the
understanding of the flow's state. For encrypted flows, this | signals used by endpoints to manage the flow's state mechanics,
divergence is not detectable by on-path devices [RFC8558]. | they may be falsified by an endpoint without affecting the peer's
| understanding of the flow's state. For encrypted flows, this
| divergence is not detectable by on-path devices.
6. Addition of Transport OAM Information to Network-Layer Headers 6. Addition of Transport OAM Information to Network-Layer Headers
Even when the transport headers are encrypted, on-path devices can Even when the transport headers are encrypted, on-path devices can
make measurements by utilising additional protocol headers carrying make measurements by utilising additional protocol headers carrying
OAM information in an additional packet header. OAM information can OAM information in an additional packet header. OAM information can
be included with packets to perform functions such as identification be included with packets to perform functions, such as identification
of transport protocols and flows, to aide understanding of network or of transport protocols and flows, to aide understanding of network or
transport performance, or to support network operations or mitigate transport performance or to support network operations or mitigate
the effects of specific network segments. the effects of specific network segments.
Using network-layer approaches to reveal information has the Using network-layer approaches to reveal information has the
potential that the same method (and hence same observation and potential that the same method (and hence same observation and
analysis tools) can be consistently used by multiple transport analysis tools) can be consistently used by multiple transport
protocols. This approach also could be applied to methods beyond OAM protocols. This approach also could be applied to methods beyond OAM
(see Section 5). There can also be less desirable implications from (see Section 5). There can also be less desirable implications from
separating the operation of the transport protocol from the separating the operation of the transport protocol from the
measurement framework. measurement framework.
6.1. Use of OAM within a Maintenance Domain 6.1. Use of OAM within a Maintenance Domain
OAM information can be restricted to a maintenance domain, typically OAM information can be restricted to a maintenance domain, typically
owned and operated by a single entity. OAM information can be added owned and operated by a single entity. OAM information can be added
at the ingress to the maintenance domain (e.g., an Ethernet protocol at the ingress to the maintenance domain (e.g., an Ethernet protocol
header with timestamps and sequence number information using a method header with timestamps and sequence number information using a method
such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data], or as a such as 802.11ag or in-situ OAM [IOAM-DATA] or as a part of the
part of the encapsulation protocol). This additional header encapsulation protocol). This additional header information is not
information is not delivered to the endpoints and is typically delivered to the endpoints and is typically removed at the egress of
removed at the egress of the maintenance domain. the maintenance domain.
Although some types of measurements are supported, this approach does Although some types of measurements are supported, this approach does
not cover the entire range of measurements described in this not cover the entire range of measurements described in this
document. In some cases, it can be difficult to position measurement document. In some cases, it can be difficult to position measurement
tools at the appropriate segments/nodes and there can be challenges tools at the appropriate segments/nodes, and there can be challenges
in correlating the downstream/upstream information when in-band OAM in correlating the downstream/upstream information when in-band OAM
data is inserted by an on-path device. data is inserted by an on-path device.
6.2. Use of OAM across Multiple Maintenance Domains 6.2. Use of OAM across Multiple Maintenance Domains
OAM information can also be added at the network layer by the sender OAM information can also be added at the network layer by the sender
as an IPv6 extension header or an IPv4 option, or in an as an IPv6 extension header or an IPv4 option or in an encapsulation/
encapsulation/tunnel header that also includes an extension header or tunnel header that also includes an extension header or option. This
option. This information can be used across multiple network information can be used across multiple network segments or between
segments, or between the transport endpoints. the transport endpoints.
One example is the IPv6 Performance and Diagnostic Metrics (PDM) One example is the IPv6 Performance and Diagnostic Metrics (PDM)
destination option [RFC8250]. This allows a sender to optionally destination option [RFC8250]. This allows a sender to optionally
include a destination option that carries header fields that can be include a destination option that carries header fields that can be
used to observe timestamps and packet sequence numbers. This used to observe timestamps and packet sequence numbers. This
information could be authenticated by a receiving transport endpoint information could be authenticated by a receiving transport endpoint
when the information is added at the sender and visible at the when the information is added at the sender and visible at the
receiving endpoint, although methods to do this have not currently receiving endpoint, although methods to do this have not currently
been proposed. This needs to be explicitly enabled at the sender. been proposed. This needs to be explicitly enabled at the sender.
7. Conclusions 7. Conclusions
Header encryption and strong integrity checks are being incorporated Header authentication and encryption and strong integrity checks are
into new transport protocols and have important benefits. The pace being incorporated into new transport protocols and have important
of development of transports using the WebRTC data channel, and the benefits. The pace of the development of transports using the WebRTC
rapid deployment of the QUIC transport protocol, can both be data channel and the rapid deployment of the QUIC transport protocol
attributed to using the combination of UDP as a substrate while can both be attributed to using the combination of UDP as a substrate
providing confidentiality and authentication of the encapsulated while providing confidentiality and authentication of the
transport headers and payload. encapsulated transport headers and payload.
This document has described some current practises, and the This document has described some current practises, and the
implications for some stakeholders, when transport layer header implications for some stakeholders, when transport-layer header
encryption is used. It does not judge whether these practises are encryption is used. It does not judge whether these practises are
necessary, or endorse the use of any specific practise. Rather, the necessary or endorse the use of any specific practise. Rather, the
intent is to highlight operational tools and practises to consider intent is to highlight operational tools and practises to consider
when designing and modifying transport protocols, so protocol when designing and modifying transport protocols, so protocol
designers can make informed choices about what transport header designers can make informed choices about what transport header
fields to encrypt, and whether it might be beneficial to make an fields to encrypt and whether it might be beneficial to make an
explicit choice to expose certain fields to devices on the network explicit choice to expose certain fields to devices on the network
path. In making such a decision, it is important to balance: path. In making such a decision, it is important to balance:
o User Privacy: The less transport header information that is User Privacy:
exposed to the network, the lower the risk of leaking metadata The less transport header information that is exposed to the
that might have user privacy implications. Transports that chose network, the lower the risk of leaking metadata that might have
to expose some header fields need to make a privacy assessment to user privacy implications. Transports that chose to expose some
understand the privacy cost versus benefit trade-off in making header fields need to make a privacy assessment to understand the
that information available. The design of the QUIC spin bit to privacy cost versus benefit trade-off in making that information
the network is an example of such considered analysis. available. The design of the QUIC spin bit to the network is an
example of such considered analysis.
o Transport Ossification: Unencrypted transport header fields are Transport Ossification:
likely to ossify rapidly, as network devices come to rely on their Unencrypted transport header fields are likely to ossify rapidly,
presence, making it difficult to change the transport in future. as network devices come to rely on their presence, making it
This argues that the choice to expose information to the network difficult to change the transport in future. This argues that the
is made deliberately and with care, since it is essentially choice to expose information to the network is made deliberately
defining a stable interface between the transport and the network. and with care, since it is essentially defining a stable interface
Some protocols will want to make that interface as limited as between the transport and the network. Some protocols will want
possible; other protocols might find value in exposing certain to make that interface as limited as possible; other protocols
information to signal to the network, or in allowing the network might find value in exposing certain information to signal to the
to change certain header fields as signals to the transport. The network or in allowing the network to change certain header fields
visible wire image of a protocol should be explicitly designed. as signals to the transport. The visible wire image of a protocol
should be explicitly designed.
o Network Ossification: While encryption can reduce ossification of Network Ossification:
the transport protocol, it does not itself prevent ossification of While encryption can reduce ossification of the transport
the network service. People seeking to understand network traffic protocol, it does not itself prevent ossification of the network
could still come to rely on pattern inferences and other service. People seeking to understand network traffic could still
heuristics or machine learning to derive measurement data and as come to rely on pattern inferences and other heuristics or machine
the basis for network forwarding decisions [RFC8546]. This learning to derive measurement data and as the basis for network
creates dependencies on the transport protocol, or the patterns of forwarding decisions [RFC8546]. This creates dependencies on the
traffic it can generate, resulting in ossification of the service. transport protocol or the patterns of traffic it can generate,
resulting in ossification of the service.
o Impact on Operational Practice: The network operations community Impact on Operational Practice:
has long relied on being able to understand Internet traffic The network operations community has long relied on being able to
patterns, both in aggregate and at the flow level, to support understand Internet traffic patterns, both in aggregate and at the
network management, traffic engineering, and troubleshooting. flow level, to support network management, traffic engineering,
Operational practice has developed based on the information and troubleshooting. Operational practice has developed based on
available from unencrypted transport headers. The IETF has the information available from unencrypted transport headers. The
supported this practice by developing operations and management IETF has supported this practice by developing operations and
specifications, interface specifications, and associated Best management specifications, interface specifications, and
Current Practises. Widespread deployment of transport protocols associated Best Current Practices. Widespread deployment of
that encrypt their information will impact network operations, transport protocols that encrypt their information will impact
unless operators can develop alternative practises that work network operations unless operators can develop alternative
without access to the transport header. practises that work without access to the transport header.
o Pace of Evolution: Removing obstacles to change can enable an Pace of Evolution:
increased pace of evolution. If a protocol changes its transport Removing obstacles to change can enable an increased pace of
header format (wire image), or its transport behaviour, this can evolution. If a protocol changes its transport header format
result in the currently deployed tools and methods becoming no (wire image) or its transport behaviour, this can result in the
longer relevant. Where this needs to be accompanied by currently deployed tools and methods becoming no longer relevant.
development of appropriate operational support functions and Where this needs to be accompanied by development of appropriate
procedures, it can incur a cost in new tooling to catch-up with operational support functions and procedures, it can incur a cost
each change. Protocols that consistently expose observable data in new tooling to catch up with each change. Protocols that
do not require such development, but can suffer from ossification consistently expose observable data do not require such
and need to consider if the exposed protocol metadata has privacy development but can suffer from ossification and need to consider
implications. There is no single deployment context, and if the exposed protocol metadata has privacy implications. There
therefore designers need to consider the diversity of operational is no single deployment context; therefore, designers need to
networks (ISPs, enterprises, DDoS mitigation and firewall consider the diversity of operational networks (ISPs, enterprises,
maintainers, etc.). DDoS mitigation and firewall maintainers, etc.).
o Supporting Common Specifications: Common, open, transport Supporting Common Specifications:
specifications can stimulate engagement by developers, users, Common, open, transport specifications can stimulate engagement by
researchers, and the broader community. Increased protocol developers, users, researchers, and the broader community.
diversity can be beneficial in meeting new requirements, but the Increased protocol diversity can be beneficial in meeting new
ability to innovate without public scrutiny risks point solutions requirements, but the ability to innovate without public scrutiny
that optimise for specific cases, and that can accidentally risks point solutions that optimise for specific cases and that
disrupt operations of/in different parts of the network. The can accidentally disrupt operations of/in different parts of the
social contract that maintains the stability of the Internet network. The social contract that maintains the stability of the
relies on accepting common transport specifications, and on it Internet relies on accepting common transport specifications and
being possible to detect violations. The existence of independent on it being possible to detect violations. The existence of
measurements, transparency, and public scrutiny of transport independent measurements, transparency, and public scrutiny of
protocol behaviour, help the community to enforce the social norm transport protocol behaviour helps the community to enforce the
that protocol implementations behave fairly and conform (at least social norm that protocol implementations behave fairly and
mostly) to the specifications. It is important to find new ways conform (at least mostly) to the specifications. It is important
of maintaining that community trust as increased use of transport to find new ways of maintaining that community trust as increased
header encryption limits visibility into transport behaviour (see use of transport header encryption limits visibility into
also Section 5.3). transport behaviour (see also Section 5.3).
o Impact on Benchmarking and Understanding Feature Interactions: An Impact on Benchmarking and Understanding Feature Interactions:
appropriate vantage point for observation, coupled with timing An appropriate vantage point for observation, coupled with timing
information about traffic flows, provides a valuable tool for information about traffic flows, provides a valuable tool for
benchmarking network devices, endpoint stacks, and/or benchmarking network devices, endpoint stacks, and/or
configurations. This can help understand complex feature configurations. This can help understand complex feature
interactions. An inability to observe transport header interactions. An inability to observe transport header
information can make it harder to diagnose and explore information can make it harder to diagnose and explore
interactions between features at different protocol layers, a interactions between features at different protocol layers, a side
side-effect of not allowing a choice of vantage point from which effect of not allowing a choice of vantage point from which this
this information is observed. New approaches might have to be information is observed. New approaches might have to be
developed. developed.
o Impact on Research and Development: Hiding transport header Impact on Research and Development:
information can impede independent research into new mechanisms, Hiding transport header information can impede independent
measurement of behaviour, and development initiatives. Experience research into new mechanisms, measurements of behaviour, and
shows that transport protocols are complicated to design and development initiatives. Experience shows that transport
complex to deploy, and that individual mechanisms have to be protocols are complicated to design and complex to deploy and that
evaluated while considering other mechanisms, across a broad range individual mechanisms have to be evaluated while considering other
of network topologies and with attention to the impact on traffic mechanisms across a broad range of network topologies and with
sharing the capacity. If increased use of transport header attention to the impact on traffic sharing the capacity. If
encryption results in reduced availability of open data, it could increased use of transport header encryption results in reduced
eliminate the independent checks to the standardisation process availability of open data, it could eliminate the independent
that have previously been in place from research and academic checks to the standardisation process that have previously been in
contributors (e.g., the role of the IRTF Internet Congestion place from research and academic contributors (e.g., the role of
Control Research Group (ICCRG) and research publications in the IRTF Internet Congestion Control Research Group (ICCRG) and
reviewing new transport mechanisms and assessing the impact of research publications in reviewing new transport mechanisms and
their deployment). assessing the impact of their deployment).
Observable transport header information might be useful to various Observable transport header information might be useful to various
stakeholders. Other sets of stakeholders have incentives to limit stakeholders. Other sets of stakeholders have incentives to limit
what can be observed. This document does not make recommendations what can be observed. This document does not make recommendations
about what information ought to be exposed, to whom it ought to be about what information ought to be exposed, to whom it ought to be
observable, or how this will be achieved. There are also design observable, or how this will be achieved. There are also design
choices about where observable fields are placed. For example, one choices about where observable fields are placed. For example, one
location could be a part of the transport header outside of the location could be a part of the transport header outside of the
encryption envelope, another alternative is to carry the information encryption envelope; another alternative is to carry the information
in a network-layer option or extension header. New transport in a network-layer option or extension header. New transport
protocol designs ought to explicitly identify any fields that are protocol designs ought to explicitly identify any fields that are
intended to be observed, consider if there are alternative ways of intended to be observed, consider if there are alternative ways of
providing the information, and reflect on the implications of providing the information, and reflect on the implications of
observable fields being used by on-path network devices, and how this observable fields being used by on-path network devices and how this
might impact user privacy and protocol evolution when these fields might impact user privacy and protocol evolution when these fields
become ossified. become ossified.
As [RFC7258] notes, "Making networks unmanageable to mitigate As [RFC7258] notes, "Making networks unmanageable to mitigate PM is
(pervasive monitoring) is not an acceptable outcome, but ignoring not an acceptable outcome, but ignoring PM would go against the
(pervasive monitoring) would go against the consensus documented consensus documented here." Providing explicit information can help
here." Providing explicit information can help avoid traffic being avoid traffic being inappropriately classified, impacting application
inappropriately classified, impacting application performance. An performance. An appropriate balance will emerge over time as real
appropriate balance will emerge over time as real instances of this instances of this tension are analysed [RFC7258]. This balance
tension are analysed [RFC7258]. This balance between information between information exposed and information hidden ought to be
exposed and information hidden ought to be carefully considered when carefully considered when specifying new transport protocols.
specifying new transport protocols.
8. Security Considerations 8. Security Considerations
This document is about design and deployment considerations for This document is about design and deployment considerations for
transport protocols. Issues relating to security are discussed transport protocols. Issues relating to security are discussed
throughout this document. throughout this document.
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently are identified as transport features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol [RFC8922]. protocol or layer on top of the transport protocol [RFC8922].
Confidentiality and strong integrity checks have properties that can Confidentiality and strong integrity checks have properties that can
also be incorporated into the design of a transport protocol or to also be incorporated into the design of a transport protocol or to
modify an existing transport. Integrity checks can protect an modify an existing transport. Integrity checks can protect an
endpoint from undetected modification of protocol fields by on-path endpoint from undetected modification of protocol fields by on-path
network devices, whereas encryption and obfuscation or greasing can network devices, whereas encryption and obfuscation or greasing can
further prevent these headers being utilised by network devices further prevent these headers being utilised by network devices
[RFC8701]. Preventing observation of headers provides an opportunity [RFC8701]. Preventing observation of headers provides an opportunity
for greater freedom to update the protocols and can ease for greater freedom to update the protocols and can ease
experimentation with new techniques and their final deployment in experimentation with new techniques and their final deployment in
endpoints. A protocol specification needs to weigh the costs of endpoints. A protocol specification needs to weigh the costs of
ossifying common headers, versus the potential benefits of exposing ossifying common headers versus the potential benefits of exposing
specific information that could be observed along the network path to specific information that could be observed along the network path to
provide tools to manage new variants of protocols. provide tools to manage new variants of protocols.
Header encryption can provide confidentiality of some or all of the Header encryption can provide confidentiality of some or all of the
transport header information. This prevents an on-path device from transport header information. This prevents an on-path device from
gaining knowledge of the header field. It therefore prevents gaining knowledge of the header field. It therefore prevents
mechanisms being built that directly rely on the information or seeks mechanisms being built that directly rely on the information or seeks
to infer semantics of an exposed header field. Reduced visibility to infer semantics of an exposed header field. Reduced visibility
into transport metadata can limit the ability to measure and into transport metadata can limit the ability to measure and
characterise traffic, and conversely can provide privacy benefits. characterise traffic and conversely can provide privacy benefits.
Extending the transport payload security context to also include the Extending the transport payload security context to also include the
transport protocol header protects both types of information with the transport protocol header protects both types of information with the
same key. A privacy concern would arise if this key was shared with same key. A privacy concern would arise if this key was shared with
a third party, e.g., providing access to transport header information a third party, e.g., providing access to transport header information
to debug a performance issue, would also result in exposing the to debug a performance issue would also result in exposing the
transport payload data to the same third party. Such risks would be transport payload data to the same third party. Such risks would be
mitigated using a layered security design that provides one domain of mitigated using a layered security design that provides one domain of
protection and associated keys for the transport payload and protection and associated keys for the transport payload and
encrypted transport headers; and a separate domain of protection and encrypted transport headers and a separate domain of protection and
associated keys for any observable transport header fields. associated keys for any observable transport header fields.
Exposed transport headers are sometimes utilised as a part of the Exposed transport headers are sometimes utilised as a part of the
information to detect anomalies in network traffic. "While PM is an information to detect anomalies in network traffic. As stated in
attack, other forms of monitoring that might fit the definition of PM [RFC7258], "While PM is an attack, other forms of monitoring that
can be beneficial and not part of any attack, e.g., network might fit the definition of PM can be beneficial and not part of any
management functions monitor packets or flows and anti-spam attack, e.g., network management functions monitor packets or flows
mechanisms need to see mail message content." [RFC7258]. This can and anti-spam mechanisms need to see mail message content." This can
be used as the first line of defence to identify potential threats be used as the first line of defence to identify potential threats
from DoS or malware and redirect suspect traffic to dedicated nodes from DoS or malware and redirect suspect traffic to dedicated nodes
responsible for DoS analysis, malware detection, or to perform packet responsible for DoS analysis, for malware detection, or to perform
"scrubbing" (the normalisation of packets so that there are no packet "scrubbing" (the normalisation of packets so that there are no
ambiguities in interpretation by the ultimate destination of the ambiguities in interpretation by the ultimate destination of the
packet). These techniques are currently used by some operators to packet). These techniques are currently used by some operators to
also defend from distributed DoS attacks. also defend from distributed DoS attacks.
Exposed transport header fields can also form a part of the Exposed transport header fields can also form a part of the
information used by the receiver of a transport protocol to protect information used by the receiver of a transport protocol to protect
the transport layer from data injection by an attacker. In the transport layer from data injection by an attacker. In
evaluating this use of exposed header information, it is important to evaluating this use of exposed header information, it is important to
consider whether it introduces a significant DoS threat. For consider whether it introduces a significant DoS threat. For
example, an attacker could construct a DoS attack by sending packets example, an attacker could construct a DoS attack by sending packets
skipping to change at page 35, line 38 skipping to change at line 1663
of sequence numbers at the receiving endpoint. This would then of sequence numbers at the receiving endpoint. This would then
introduce additional work at the receiving endpoint, even though the introduce additional work at the receiving endpoint, even though the
data in the attacking packet might not finally be delivered by the data in the attacking packet might not finally be delivered by the
transport layer. This is sometimes known as a "shadowing attack". transport layer. This is sometimes known as a "shadowing attack".
An attack can, for example, disrupt receiver processing, trigger loss An attack can, for example, disrupt receiver processing, trigger loss
and retransmission, or make a receiving endpoint perform unproductive and retransmission, or make a receiving endpoint perform unproductive
decryption of packets that cannot be successfully decrypted (forcing decryption of packets that cannot be successfully decrypted (forcing
a receiver to commit decryption resources, or to update and then a receiver to commit decryption resources, or to update and then
restore protocol state). restore protocol state).
One mitigation to off-path attack is to deny knowledge of what header One mitigation to off-path attacks is to deny knowledge of what
information is accepted by a receiver or obfuscate the accepted header information is accepted by a receiver or obfuscate the
header information, e.g., setting a non-predictable initial value for accepted header information, e.g., setting a nonpredictable initial
a sequence number during a protocol handshake, as in [RFC3550] and value for a sequence number during a protocol handshake, as in
[RFC6056], or a port value that cannot be predicted (see Section 5.1 [RFC3550] and [RFC6056], or a port value that cannot be predicted
of [RFC8085]). A receiver could also require additional information (see Section 5.1 of [RFC8085]). A receiver could also require
to be used as a part of a validation check before accepting packets additional information to be used as a part of a validation check
at the transport layer (e.g., utilising a part of the sequence number before accepting packets at the transport layer, e.g., utilising a
space that is encrypted; or by verifying an encrypted token not part of the sequence number space that is encrypted or by verifying
visible to an attacker). This would also mitigate against on-path an encrypted token not visible to an attacker. This would also
attacks. An additional processing cost can be incurred when mitigate against on-path attacks. An additional processing cost can
decryption is attempted before a receiver discards an injected be incurred when decryption is attempted before a receiver discards
packet. an injected packet.
The existence of open transport protocol standards, and a research The existence of open transport protocol standards and a research and
and operations community with a history of independent observation operations community with a history of independent observation and
and evaluation of performance data, encourages fairness and evaluation of performance data encourage fairness and conformance to
conformance to those standards. This suggests careful consideration those standards. This suggests careful consideration will be made
will be made over where, and when, measurement samples are collected. over where, and when, measurement samples are collected. An
An appropriate balance between encrypting some or all of the appropriate balance between encrypting some or all of the transport
transport header information needs to be considered. Open data, and header information needs to be considered. Open data and
accessibility to tools that can help understand trends in application accessibility to tools that can help understand trends in application
deployment, network traffic and usage patterns can all contribute to deployment, network traffic, and usage patterns can all contribute to
understanding security challenges. understanding security challenges.
The Security and Privacy Considerations in the Framework for Large- The security and privacy considerations in "A Framework for Large-
Scale Measurement of Broadband Performance (LMAP) [RFC7594] contain Scale Measurement of Broadband Performance (LMAP)" [RFC7594] contain
considerations for Active and Passive measurement techniques and considerations for Active and Passive measurement techniques and
supporting material on measurement context. supporting material on measurement context.
Addition of observable transport information to the path increases Addition of observable transport information to the path increases
the information available to an observer and may, when this the information available to an observer and may, when this
information can be linked to a node or user, reduce the privacy of information can be linked to a node or user, reduce the privacy of
the user. See the security considerations of [RFC8558]. the user. See the security considerations of [RFC8558].
9. IANA Considerations 9. IANA Considerations
This memo includes no request to IANA. This document has no IANA actions.
10. Acknowledgements
The authors would like to thank Mohamed Boucadair, Spencer Dawkins,
Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen
Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, Chris
Wood, Thomas Fossati, Mohamed Boucadair, Martin Thomson, David Black,
Martin Duke, Joel Halpern and members of TSVWG for their comments and
feedback.
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No 688421,
and the EU Stand ICT Call 4. The opinions expressed and arguments
employed reflect only the authors' view. The European Commission is
not responsible for any use that might be made of that information.
This work has received funding from the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1.
11. Informative References 10. Informative References
[bufferbloat] [bufferbloat]
Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in Gettys, J. and K. Nichols, "Bufferbloat: Dark Buffers in
the Internet. Communications of the ACM, 55(1):57-65", the Internet", Communications of the ACM, Vol. 55, no. 1,
January 2012. pp. 57-65, DOI 10.1145/2063176.2063196, January 2012,
<https://doi.org/10.1145/2063176.2063196>.
[I-D.ietf-6man-ipv6-alt-mark]
Fioccola, G., Zhou, T., Cociglio, M., and F. Qin, "IPv6
Application of the Alternate Marking Method", draft-ietf-
6man-ipv6-alt-mark-00 (work in progress), May 2020.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-10 (work in
progress), July 2020.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-29 (work
in progress), June 2020.
[I-D.ietf-tls-dtls13] [DTLS] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-38 (work in progress), May 1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
2020. dtls13-43, 30 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
[I-D.ietf-tsvwg-rtcweb-qos] dtls13-43>.
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-18 (work in progress), August 2016.
[I-D.marx-qlog-main-schema] [IOAM-DATA]
Marx, R., "Main logging schema for qlog", draft-marx-qlog- Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
main-schema-02 (work in progress), November 2020. for In-situ OAM", Work in Progress, Internet-Draft, draft-
ietf-ippm-ioam-data-12, 21 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-ippm-
ioam-data-12>.
[I-D.trammell-plus-abstract-mech] [IPV6-ALT-MARK]
Trammell, B., "Abstract Mechanisms for a Cooperative Path Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
Layer under Endpoint Control", draft-trammell-plus- Pang, "IPv6 Application of the Alternate Marking Method",
abstract-mech-00 (work in progress), September 2016. Work in Progress, Internet-Draft, draft-ietf-6man-ipv6-
alt-mark-06, 31 May 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-
ipv6-alt-mark-06>.
[Latency] Briscoe, B., "Reducing Internet Latency: A Survey of [Latency] Briscoe, B., Brunstrom, A., Petlund, A., Hayes, D., Ros,
Techniques and Their Merits, IEEE Comm. Surveys & D., Tsang, I., Gjessing, S., Fairhurst, G., Griwodz, C.,
Tutorials. 26;18(3) p2149-2196", November 2014. and M. Welzl, "Reducing Internet Latency: A Survey of
Techniques and Their Merits", IEEE Communications Surveys
& Tutorials, vol. 18, no. 3, pp. 2149-2196, thirdquarter
2016, DOI 10.1109/COMST.2014.2375213, November 2014,
<https://doi.org/10.1109/COMST.2014.2375213>.
[Measurement] [Measurement]
Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement- Fairhurst, G., Kuehlewind, M., and D. Lopez, "Measurement-
based Protocol Design, Eur. Conf. on Networks and based Protocol Design", European Conference on Networks
Communications, Oulu, Finland.", June 2017. and Communications, Oulu, Finland., June 2017.
[PAM-RTT] Trammell, B. and M. Kuehlewind, "Revisiting the Privacy [PAM-RTT] Trammell, B. and M. Kuehlewind, "Revisiting the Privacy
Implications of Two-Way Internet Latency Data (in Proc. Implications of Two-Way Internet Latency Data", Passive
PAM 2018)", March 2018. and Active Measurement, March 2018.
[PLUS-ABSTRACT-MECH]
Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", Work in Progress, Internet-
Draft, draft-trammell-plus-abstract-mech-00, 28 September
2016, <https://datatracker.ietf.org/doc/html/draft-
trammell-plus-abstract-mech-00>.
[QLOG] Marx, R., Niccolini, L., and M. Seemann, "Main logging
schema for qlog", Work in Progress, Internet-Draft, draft-
ietf-quic-qlog-main-schema-00, 10 June 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
qlog-main-schema-00>.
[Quic-Trace] [Quic-Trace]
"https:QUIC trace utilities //github.com/google/quic- "QUIC trace utilities",
trace". <https://github.com/google/quic-trace>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981, DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>. <https://www.rfc-editor.org/info/rfc791>.
[RFC2410] Glenn, R. and S. Kent, "The NULL Encryption Algorithm and [RFC2410] Glenn, R. and S. Kent, "The NULL Encryption Algorithm and
Its Use With IPsec", RFC 2410, DOI 10.17487/RFC2410, Its Use With IPsec", RFC 2410, DOI 10.17487/RFC2410,
November 1998, <https://www.rfc-editor.org/info/rfc2410>. November 1998, <https://www.rfc-editor.org/info/rfc2410>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
skipping to change at page 39, line 39 skipping to change at line 1841
<https://www.rfc-editor.org/info/rfc3711>. <https://www.rfc-editor.org/info/rfc3711>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, [RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005, DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>. <https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005, RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>. <https://www.rfc-editor.org/info/rfc4303>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/rfc4566>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006, DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>. <https://www.rfc-editor.org/info/rfc4585>.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, [RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737, S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
DOI 10.17487/RFC4737, November 2006, DOI 10.17487/RFC4737, November 2006,
<https://www.rfc-editor.org/info/rfc4737>. <https://www.rfc-editor.org/info/rfc4737>.
skipping to change at page 44, line 44 skipping to change at line 2086
Paasch, "TCP Extensions for Multipath Operation with Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/info/rfc8684>. 2020, <https://www.rfc-editor.org/info/rfc8684>.
[RFC8701] Benjamin, D., "Applying Generate Random Extensions And [RFC8701] Benjamin, D., "Applying Generate Random Extensions And
Sustain Extensibility (GREASE) to TLS Extensibility", Sustain Extensibility (GREASE) to TLS Extensibility",
RFC 8701, DOI 10.17487/RFC8701, January 2020, RFC 8701, DOI 10.17487/RFC8701, January 2020,
<https://www.rfc-editor.org/info/rfc8701>. <https://www.rfc-editor.org/info/rfc8701>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header Zúñiga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724, Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020, DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>. <https://www.rfc-editor.org/info/rfc8724>.
[RFC8837] Jones, P., Dhesikan, S., Jennings, C., and D. Druta, [RFC8837] Jones, P., Dhesikan, S., Jennings, C., and D. Druta,
"Differentiated Services Code Point (DSCP) Packet Markings "Differentiated Services Code Point (DSCP) Packet Markings
for WebRTC QoS", RFC 8837, DOI 10.17487/RFC8837, January for WebRTC QoS", RFC 8837, DOI 10.17487/RFC8837, January
2021, <https://www.rfc-editor.org/info/rfc8837>. 2021, <https://www.rfc-editor.org/info/rfc8837>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
[RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C. [RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C.
Wood, "A Survey of the Interaction between Security Wood, "A Survey of the Interaction between Security
Protocols and Transport Services", RFC 8922, Protocols and Transport Services", RFC 8922,
DOI 10.17487/RFC8922, October 2020, DOI 10.17487/RFC8922, October 2020,
<https://www.rfc-editor.org/info/rfc8922>. <https://www.rfc-editor.org/info/rfc8922>.
Appendix A. Revision information [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
-00 This is an individual draft for the IETF community. DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
-01 This draft was a result of walking away from the text for a few
days and then reorganising the content.
-02 This draft fixes textual errors.
-03 This draft follows feedback from people reading this draft.
-04 This adds an additional contributor and includes significant
reworking to ready this for review by the wider IETF community Colin
Perkins joined the author list.
Comments from the community are welcome on the text and
recommendations.
-05 Corrections received and helpful inputs from Mohamed Boucadair.
-06 Updated following comments from Stephen Farrell, and feedback via
email. Added a draft conclusion section to sketch some strawman
scenarios that could emerge.
-07 Updated following comments from Al Morton, Chris Seal, and other
feedback via email.
-08 Updated to address comments sent to the TSVWG mailing list by
Kathleen Moriarty (on 08/05/2018 and 17/05/2018), Joe Touch on
11/05/2018, and Spencer Dawkins.
-09 Updated security considerations.
-10 Updated references, split the Introduction, and added a paragraph
giving some examples of why ossification has been an issue.
-01 This resolved some reference issues. Updated section on
observation by devices on the path.
-02 Comments received from Kyle Rose, Spencer Dawkins and Tom
Herbert. The network-layer information has also been re-organised
after comments at IETF-103.
-03 Added a section on header compression and rewriting of sections
referring to RTP transport. This version contains author editorial
work and removed duplicate section.
-04 Revised following SecDir Review
o Added some text on TLS story (additional input sought on relevant
considerations).
o Section 2, paragraph 8 - changed to be clearer, in particular,
added "Encryption with secure key distribution prevents"
o Flow label description rewritten based on PS/BCP RFCs.
o Clarify requirements from RFCs concerning the IPv6 flow label and
highlight ways it can be used with encryption. (section 3.1.3)
o Add text on the explicit spin-bit work in the QUIC DT. Added
greasing of spin-bit. (Section 6.1)
o Updated section 6 and added more explanation of impact on
operators.
o Other comments addressed.
-05 Editorial pass and minor corrections noted on TSVWG list.
-06 Updated conclusions and minor corrections. Responded to request
to add OAM discussion to Section 6.1.
-07 Addressed feedback from Ruediger and Thomas.
Section 2 deserved some work to make it easier to read and avoid
repetition. This edit finally gets to this, and eliminates some
duplication. This also moves some of the material from section 2 to
reform a clearer conclusion. The scope remains focussed on the usage
of transport headers and the implications of encryption - not on
proposals for new techniques/specifications to be developed.
-08 Addressed feedback and completed editorial work, including
updating the text referring to RFC7872, in preparation for a WGLC.
-09 Updated following WGLC. In particular, thanks to Joe Touch
(specific comments and commentary on style and tone); Dimitri Tikonov
(editorial); Christian Huitema (various); David Black (various).
Amended privacy considerations based on SECDIR review. Emile Stephan
(inputs on operations measurement); Various others.
Added summary text and refs to key sections. Note to editors: The
section numbers are hard-linked.
-10 Updated following additional feedback from 1st WGLC. Comments
from David Black; Tommy Pauly; Ian Swett; Mirja Kuehlewind; Peter
Gutmann; Ekr; and many others via the TSVWG list. Some people
thought that "needed" and "need" could
represent requirements in the document, etc. this has been clarified.
-11 Updated following additional feedback from Martin Thomson, and
corrections from other reviewers.
-12 Updated following additional feedback from reviewers.
-13 Updated following 2nd WGLC with comments from D.L.Black; T.
Herbert; Ekr; and other reviewers.
-14 Update to resolve feedback to rev -13. This moves the general
discussion of adding fields to transport packets to section 6, and
discusses with reference to material in RFC8558.
-15 Feedback from D.L. Black, T. Herbert, J. Touch, S. Dawkins
and M. Duke. Update to add reference to RFC7605. Clarify a focus
on immutable transport fields, rather than modifying middleboxes with
Tom H. Clarified Header Compression discussion only provides a list
of examples of HC methods for transport. Clarified port usage with
Tom H/Joe T. Removed some duplicated sentences, and minor edits.
Added NULL-ESP. Improved after initial feedback from Martin Duke.
-16 Editorial comments from Mohamed Boucadair. Added DTLS 1.3.
-17 Revised to satisfy ID-NITs and updates REFs to latest rev,
updated HC Refs; cited IAB guidance on security and privacy within
IETF specs.
-18 Revised based on AD review.
-19 Revised after additional AD review request, and request to
restructure.
-20 Revised after directorate reviews and IETF LC comments.
Gen-ART:
o While section 2 does include a discussion of traffic mis-ordering,
it does not include a discussion of ECMP, and the dependence of
ECMP on flow identification to avoid significant packet mis-
ordering.:: ECMP added as example.
o Section 5.1 of this document discusses the use of Hop-by-Hop IPv6
options. It seems that it should acknowledge and discuss the
applicability of the sentence "New hop-by-hop options are not
recommended..." from section 4.8 of RFC 8200. I think a good
argument can be made in this case as to why (based on the rest of
the sentence from 8200) the recommendation does not apply to this
proposal. The document should make the argument.:: Quoted RFC
sentences directly to avoid interpretting them.
o I found the discussion of header compression slightly confusing.
Given that the TCP / UDP header is small even compared to the IP
header, it is difficult to see why encrypting it would have a
significant impact on header compression efficacy. :: Added a
preface that explains that HC methods are most effective for bit-
congestive links.
o The wording in section 6.2 on adding header information to an IP
packet has the drawback of seeming to imply that one could add (or
remove) such information in the network, without adding an
encapsulating header. That is not permitted by RFC 8200 (IPv6).
It would be good to clarify the first paragraph. (The example,
which talks about the sender putting in the information is, of
course, fine.) :: Unintended - added a sentence of preface.
SECDIR:: Previous revisions were updated following Early Review
comments.
OPSEC:: No additional changes were requested in the OPSEC review.
IETF LC:: Tom Herbert: Please refer to 8200 on EH :: addressed in Acknowledgements
response to Joel above. Michael Richardson, Fernando Gont, Tom
Herbert: Continuation of discussion on domains where EH might be (or
not) useful and the tussle on what information to reveal. Unclear
yet what additional text should be changed within this ID.
------------ The authors would like to thank Mohamed Boucadair, Spencer Dawkins,
Tom Herbert, Jana Iyengar, Mirja Kühlewind, Kyle Rose, Kathleen
Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, Chris
Wood, Thomas Fossati, Mohamed Boucadair, Martin Thomson, David Black,
Martin Duke, Joel Halpern, and members of TSVWG for their comments
and feedback.
- 21 Revised after IESG review: This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No 688421 and
the EU Stand ICT Call 4. The opinions expressed and arguments
employed reflect only the authors' views. The European Commission is
not responsible for any use that might be made of that information.
Revision 21 includes revised text after comments from Zahed, Erik This work has received funding from the UK Engineering and Physical
Kline, Rob Wilton, Eric Vyncke, Roman Danyliw, and Benjamin Kaduk. Sciences Research Council under grant EP/R04144X/1.
Authors' Addresses Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen AB24 3UE Aberdeen, Scotland
Scotland AB24 3UE
United Kingdom
EMail: gorry@erg.abdn.ac.uk Email: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/ URI: http://www.erg.abdn.ac.uk/
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
Glasgow G12 8QQ Glasgow, Scotland
Scotland G12 8QQ
United Kingdom
EMail: csp@csperkins.org Email: csp@csperkins.org
URI: https://csperkins.org/ URI: https://csperkins.org/
 End of changes. 229 change blocks. 
926 lines changed or deleted 768 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/