wdiff rfc8622.original rfc8622.txt

Internet Engineering Task Force (IETF) R. Bless
Internet-Draft Karlsruhe Institute of Technology (KIT)
Request for Comments: 8622 KIT
Obsoletes: 3662 (if approved) March 11, June 2019
Updates: 4594,8325 (if approved)
Intended status: 4594, 8325
Category: Standards Track
Expires: September 12, 2019
ISSN: 2070-1721

A Lower Effort Lower-Effort Per-Hop Behavior (LE PHB) for Differentiated Services
draft-ietf-tsvwg-le-phb-10

Abstract

This document specifies properties and characteristics of a Lower Lower-
Effort (LE) per-hop behavior (PHB). Per-Hop Behavior (LE PHB). The primary objective of this LE
PHB is to protect best-effort Best-Effort (BE) traffic (packets forwarded with
the default PHB) from LE traffic in congestion situations, i.e., when
resources become scarce, best-effort BE traffic has precedence over LE traffic
and may preempt it. Alternatively, packets forwarded by the LE PHB
can be associated with a scavenger service class, i.e., they scavenge otherwise unused
otherwise-unused resources only. There are numerous uses for this
PHB, e.g., for background traffic of low precedence, such as bulk
data transfers with low priority in time, non time-critical non-time-critical backups,
larger software updates, web search engines while gathering
information from web servers and so on. This document recommends a
standard DSCP Differentiated Services Code Point (DSCP) value for the LE
PHB.

This specification obsoletes RFC 3662 and updates the DSCP
recommended in RFC RFCs 4594 and RFC 8325 to use the DSCP assigned in this
specification.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 12, 2019.
https://www.rfc-editor.org/info/rfc8622.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 ....................................................3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 ...........................................3
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3 ...................................................3
4. PHB Description . . . . . . . . . . . . . . . . . . . . . . . 6 .................................................6
5. Traffic Conditioning Traffic-Conditioning Actions . . . . . . . . . . . . . . . . 7 ....................................7
6. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 7 DSCP ................................................7
7. Deployment Considerations . . . . . . . . . . . . . . . . . . 7 .......................................8
8. Remarking Re-marking to other Other DSCPs/PHBs . . . . . . . . . . . . . . . . 8 ..................................9
9. Multicast Considerations . . . . . . . . . . . . . . . . . . 9 .......................................10
10. The Update Updates to RFC 4594 . . . . . . . . . . . . . . . . . . . 10 .......................................11
11. The Update Updates to RFC 8325 . . . . . . . . . . . . . . . . . . . 12 .......................................12
12. The Update to draft-ietf-tsvwg-rtcweb-qos . . . . . . . . . . 12
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
14. ...........................................13
13. Security Considerations . . . . . . . . . . . . . . . . . . . 14
15. .......................................14
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
15.1. ....................................................15
14.1. Normative References . . . . . . . . . . . . . . . . . . 15
15.2. .....................................15
14.2. Informative References . . . . . . . . . . . . . . . . . 15 ...................................15
Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 17
Appendix B. .................................18
Acknowledgments . . . . . . . . . . . . . . . . . . 18
Appendix C. Change History . . . . . . . . . . . . . . . . . . . 18
Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 21 ...................................................18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21 ..................................................18

1. Introduction

This document defines a Differentiated Services (DS) per-hop behavior
[RFC2474] called "Lower Effort" (LE), "Lower-Effort Per-Hop Behavior" (LE PHB), which is
intended for traffic of sufficiently low urgency that all other
traffic takes precedence over the LE traffic in consumption of
network link bandwidth. Low
urgency Low-urgency traffic has a low priority for
timely forwarding, which forwarding; note, however, that this does not necessarily
imply that it is generally of minor importance. From this viewpoint,
it can be considered as a network equivalent to a background priority
for processes in an operating system. There may or may not be memory
(buffer) resources allocated for this type of traffic.

Some networks carry packets that ought to consume network resources
only when no other traffic is demanding them. In From this point of
view, packets forwarded by the LE PHB scavenge otherwise unused otherwise-unused
resources
only, which only; this led to the name "scavenger service" in early
Internet2 deployments (see Appendix A). Other commonly used names
for LE PHB
type types of services are "Lower-than-best-effort" "Lower than best effort"
[Carlberg-LBE-2001] or "Less-than-best-
effort". "Less than best effort" [Chown-LBE-2003]. In
summary, with the mentioned feature above, above-mentioned feature, the LE PHB has two
important properties: it should scavenge residual capacity capacity, and it
must be preemptable by the default PHB (or other elevated PHBs) in
case they need more resources. Consequently, the effect of this type
of traffic on all other network traffic is strictly limited
("no (the
"no harm" property). This is distinct from "best-effort" "Best-Effort" (BE)
traffic
traffic, since the network makes no commitment to deliver LE packets.
In contrast, BE traffic receives an implied "good faith" commitment
of at least some available network resources. This document proposes
a Lower Effort Differentiated Services per-hop behavior (LE PHB)
an LE DS PHB for handling this "optional" traffic in a differentiated services DS node.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119][RFC8174] [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. Applicability

A Lower Effort

An LE PHB is applicable for many applications that otherwise use best-effort BE
delivery. More specifically, it is suitable for traffic and services
that can tolerate strongly varying throughput for their data flows,
especially periods of very low throughput or even starvation (i.e.,
long interruptions due to significant or even complete packet loss).
Therefore, an application sending an LE
marked LE-marked flow needs to be able
to tolerate short or (even very) long interruptions due to the
presence of severe congestion conditions during the transmission of
the flow. Thus, there ought to be an expectation that packets of the
LE PHB could be excessively delayed or dropped when any other traffic
is present. It is application-
dependent when Whether or not a lack of progress is considered being to be a
failure is application dependent (e.g., if a transport connection
fails due to timing out, the application may try several times to re-establish
reestablish the transport connection in order to resume the
application session before finally giving up). The LE PHB is
suitable for sending traffic of low urgency across a Differentiated Services (DS) DS domain or DS
region.

Just like best-effort BE traffic, LE traffic SHOULD be congestion controlled
(i.e., use a congestion controlled transport or implement an
appropriate congestion control method [RFC2914] [RFC8085]). Since LE
traffic could be starved completely for a longer period of time,
transport protocols or applications (and their related congestion
control mechanisms) SHOULD be able to detect and react to such a
starvation situation. An appropriate reaction would be to resume the
transfer instead of aborting it, i.e., an LE optimized LE-optimized transport
ought to use appropriate retry strategies (e.g., exponential back-off
with an upper bound) as well as corresponding retry and timeout
limits in order to avoid the loss of the connection due to the
mentioned
above-mentioned starvation periods. While it is desirable to achieve
a quick resumption of the transfer as soon as resources become
available again, it may be difficult to achieve this in practice. In
the case of a lack of a transport protocol and congestion control
that are adapted to LE, applications can also use existing common
transport protocols and implement session resumption by trying to re-establish
reestablish failed connections. Congestion control is not only
useful to let for letting the flows within the LE behavior aggregate Behavior Aggregate (BA)
adapt to the available bandwidth
that bandwidth, which may be highly fluctuating, but fluctuating; it
is also essential if LE traffic is mapped to the default PHB in DS
domains that do not support LE. In this case, the use of background
transport protocols, e.g., similar to
LEDBAT Low Extra Delay Background
Transport (LEDBAT) [RFC6817], is expedient.

Use

The use of the LE PHB might assist a network operator in moving
certain kinds of traffic or users to off-peak times. Furthermore,
packets can be designated for the LE PHB when the goal is to protect
all other packet traffic from competition with the LE aggregate while
not completely banning LE traffic from the network. An LE PHB
SHOULD NOT be used for a customer's "normal Internet" traffic and
packets SHOULD NOT be "downgraded" to the LE PHB instead of being
dropped, particularly when the packets are unauthorized traffic. The
LE PHB is expected to have applicability in networks that have at
least some unused capacity at during certain periods.

The LE PHB allows networks to protect themselves from selected types
of traffic as a complement to giving preferential treatment to other
selected traffic aggregates. LE ought not to be used for the general
case of downgraded traffic, but it could be used by design, e.g., to
protect an internal network from untrusted external traffic sources.
In this case case, there is no way for attackers to preempt internal (non
LE)
(non-LE) traffic by flooding. Another use case in this regard is the
forwarding of multicast traffic from untrusted sources. Multicast
forwarding is currently enabled within domains only for specific
sources within a domain, but domain -- not for sources from anywhere in the
Internet. A One major problem is that multicast routing creates
traffic sources at (mostly) unpredictable branching points within a
domain, potentially leading to congestion and packet loss. In the
case of where multicast traffic packets from untrusted sources are
forwarded as LE traffic, they will not harm traffic from non-LE behavior aggregates. BAs.
A further related use case is mentioned in [RFC3754]: preliminary
forwarding of non-admitted multicast traffic.

There is no intrinsic reason to limit the applicability of the LE PHB
to any particular application or type of traffic. It is intended as
an additional traffic engineering tool for network administrators.
For instance, it can be used to fill protection capacity of
transmission links that is otherwise unused. Some network providers
keep link utilization below 50% to ensure that all traffic is
forwarded without loss after rerouting caused by a link failure (cf.
Section 6 of [RFC3439]). LE marked LE-marked traffic can utilize the normally
unused capacity and will be preempted automatically in the case of
link failure when 100% of the link capacity is required for all other
traffic. Ideally, applications mark their packets as LE traffic,
since
because they know the urgency of flows. Since LE traffic may be
starved for longer periods of time time, it is probably less suitable for
real-time and interactive applications.

Example uses for the LE PHB:

o For traffic caused by world-wide web World Wide Web search engines while they
gather information from web servers.

o For software updates or dissemination of new releases of operating
systems.

o For reporting errors or telemetry data from operating systems or
applications.

o For backup traffic or non-time critical synchronization traffic, non-time-critical synchronization, or
mirroring traffic.

o For content distribution transfers between caches.

o For preloading or prefetching objects from web sites.

o For network news and other "bulk mail" of the Internet.

o For "downgraded" traffic from some other PHB when this does not
violate the operational objectives of the other PHB.

o For multicast traffic from untrusted (e.g., non-local) sources.

4. PHB Description

The LE PHB is defined in relation to the default PHB (best-effort). (BE). A packet
forwarded with the LE PHB SHOULD have lower precedence than packets
forwarded with the default PHB, i.e., in the case of congestion, LE marked
LE-marked traffic SHOULD be dropped prior to dropping any default PHB
traffic. Ideally, LE packets would be forwarded only when no packet
with any other PHB is awaiting transmission. This means that in the
case of link resource contention LE traffic can be starved
completely, which may not be always be desired by the network operator's
policy. The used A scheduler used to implement the LE PHB may reflect this
policy accordingly.

A straightforward implementation could be a simple priority scheduler
serving the default PHB queue with higher priority than the lower-
effort LE PHB
queue. Alternative implementations may use scheduling algorithms
that assign a very small weight to the LE class. This, however,
could sometimes cause better service for LE packets compared to BE
packets in cases when the BE share is fully utilized and the LE share
is not.

If a dedicated LE queue is not available, an active queue management
mechanism within a common BE/LE queue could also be used. This could
drop all arriving LE packets as soon as certain queue length or
sojourn time thresholds are exceeded.

Since congestion control is also useful within the LE traffic class,
Explicit Congestion Notification (ECN) [RFC3168] SHOULD be used for
LE packets, too. More specifically, an LE implementation SHOULD also
apply CE Congestion Experienced (CE) marking for ECT marked ECT-marked packets
("ECT" stands for ECN-Capable Transport), and transport protocols
used for LE SHOULD support and employ ECN. For more information on
the benefits of using ECN ECN, see [RFC8087].

5. Traffic Conditioning Traffic-Conditioning Actions

If possible, packets SHOULD be pre-marked in DS-aware end systems by
applications due to their specific knowledge about the particular
precedence of packets. There is no incentive for DS domains to
distrust this initial marking, because letting LE traffic enter a DS
domain causes no harm. Thus, any policing policing, such as limiting the rate
of LE traffic traffic, is not necessary at the DS boundary.

As for most other PHBs PHBs, an initial classification and marking can be
also be performed at the first DS boundary node according to the DS
domain's own policies (e.g., as a protection measure against
untrusted sources). However, non-LE traffic (e.g., BE traffic)
SHOULD NOT be
remarked re-marked to LE. Remarking Re-marking traffic from another PHB
results in that traffic being "downgraded". This changes the way the
network treats this traffic traffic, and it is important not to violate the
operational objectives of the original PHB. See also remarks with respect to
downgrading in Section Sections 3 and Section 8. 8 for
notes related to downgrading.

6. Recommended DS Codepoint DSCP

The RECOMMENDED codepoint for the LE PHB is '000001'.

Earlier specifications [RFC4594] (e.g., [RFC4594]) recommended to the use CS1 of Class
Selector 1 (CS1) as the codepoint (as mentioned in [RFC3662]). This
is problematic problematic, since it may cause a priority inversion in Diffserv
domains that treat CS1 as originally proposed in [RFC2474], resulting
in forwarding LE packets with higher precedence than BE packets.
Existing implementations SHOULD transition to use the unambiguous LE
codepoint '000001' whenever possible.

This particular codepoint was chosen due to measurements on the
currently observable DSCP remarking Differentiated Services Code Point (DSCP)
re-marking behavior in the Internet
[ietf99-secchi]. [IETF99-Secchi]. Since some
network domains set the former IP
precedence Precedence bits to zero, it is
possible that some other standardized DSCPs get mapped to the LE PHB
DSCP if it were taken from the DSCP
standards action pool Standards Action Pool 1 (xxxxx0). (xxxxx0)
[RFC2474] [RFC8436].

7. Deployment Considerations

In order to enable LE support, DS nodes typically only need

o A BA classifier (Behavior Aggregate classifier, see (see [RFC2475]) that classifies packets according
to the LE DSCP

o A dedicated LE queue

o A suitable scheduling discipline, e.g., simple priority queueing

Alternatively, implementations could use active queue management
mechanisms instead of a dedicated LE queue, e.g., dropping all
arriving LE packets when certain queue length or sojourn time
thresholds are exceeded.

Internet-wide deployment of the LE PHB is eased by the following
properties:

o No harm to other traffic: since the LE PHB has the lowest
forwarding priority priority, it does not consume resources from other
PHBs. Deployment across different provider domains with LE
support causes no trust issues or attack vectors to existing (non LE)
(non-LE) traffic. Thus, providers can trust LE markings from end-systems,
end systems, i.e., there is no need to police or remark re-mark incoming
LE traffic.

o No PHB parameters or configuration of traffic profiles: the LE PHB
itself possesses no parameters that need to be set or configured.
Similarly, since LE traffic requires no admission or policing, it
is not necessary to configure traffic profiles.

o No traffic conditioning traffic-conditioning mechanisms: the LE PHB requires no traffic
meters, droppers, or shapers. See also Section 5 for further
discussion.

Operators of DS domains that cannot or do not want to implement the
LE PHB (e.g., because there is no separate LE queue available in the
corresponding nodes) SHOULD NOT drop packets marked with the LE DSCP.
They SHOULD map packets with this DSCP to the default PHB and SHOULD
preserve the LE DSCP marking. DS domains domain operators that do not
implement the LE PHB should be aware that they violate the "no harm"
property of LE. See also Section 8 for further discussion of
forwarding LE traffic with the default PHB instead. instead of the LE PHB.

8. Remarking Re-marking to other Other DSCPs/PHBs

"DSCP bleaching", i.e., setting the DSCP to '000000' (default PHB) is
NOT RECOMMENDED for this PHB. This may cause effects that are in
contrast to the original intent in protecting to protect BE traffic from LE traffic (no harm
(the "no harm" property). In the case that a DS domain does not
support the LE PHB, its nodes SHOULD treat LE marked LE-marked packets with the
default PHB instead (by mapping the LE DSCP to the default PHB), but
they SHOULD do so without remarking re-marking to DSCP '000000'. The reason for
this This is that later traversed
because DS domains that are traversed later may then have still have the
possibility
opportunity to treat such packets according to the LE PHB.

Operators of DS domains that forward LE traffic within the BE
aggregate need to be aware of the implications, i.e., induced
congestion situations and quality-of-service QoS degradation of the original BE traffic.
In this case, the LE property of not harming other traffic is no
longer fulfilled. To limit the impact in such cases, traffic
policing of the LE aggregate MAY be used.

In the case that LE marked LE-marked packets are effectively carried within with the
default PHB (i.e., forwarded as best-effort traffic) BE traffic), they get a better
forwarding treatment than expected. For some applications and
services, it is favorable if the transmission is finished earlier
than expected. However, in some cases cases, it may be against the
original intention of the LE PHB user to strictly send the traffic
only if
otherwise unused otherwise-unused resources are available. In the case that
LE traffic is mapped to the default PHB, LE traffic may compete with
BE traffic for the same resources and thus adversely affect the
original BE aggregate. Applications that want to ensure the lower
precedence compared to BE traffic even in such cases SHOULD use
additionally use a corresponding Lower-than-Best-Effort lower-than-BE transport protocol
[RFC6297], e.g., LEDBAT [RFC6817].

A DS domain that still uses DSCP CS1 for marking LE traffic
(including Low Priority-Data Low-Priority Data as defined in [RFC4594] or the old
definition in [RFC3662]) SHOULD remark re-mark traffic to the LE DSCP
'000001' at the egress to the next DS domain. This increases the
probability that the DSCP is preserved end-to-end, end to end, whereas a CS1
marked
CS1-marked packet may be remarked re-marked by the default DSCP if the next
domain is applying Diffserv-Interconnection [RFC8100].

9. Multicast Considerations

Basically, the multicast considerations in [RFC3754] apply. However,
using the Lower Effort LE PHB for multicast requires paying special attention to the way
how packets get replicated inside routers. Due to multicast packet
replication, resource contention may actually occur even before a
packet is forwarded to its output port and in port. In the worst case, these
forwarding resources are missing for higher
prioritized higher-priority multicast or
even unicast packets.

Several forward error correction coding schemes schemes, such as fountain
codes (e.g., [RFC5053]) [RFC5053]), allow reliable data delivery even in
environments with a potential potentially high amount of packet loss in
transmission. When used used, for example example, over satellite links or other
broadcast media, this means that receivers that lose 80% of packets
in transmission simply need 5 five times as long longer to receive the complete
data than those receivers experiencing no loss (without any receiver
feedback required).

Superficially viewed, it may sound very attractive to use IP
multicast with the LE PHB to build this type of opportunistic
reliable distribution in IP networks, but it can only be usefully
deployed with routers that do not experience forwarding/replication
resource starvation when a large amount of packets (virtually) need
to be replicated to links where the LE queue is full.

Thus, a packet replication of LE marked mechanism for LE-marked packets should
consider the situation at the respective output links: it is a waste
of internal forwarding resources if a packet is replicated to output
links that have no resources left for LE forwarding. In those cases cases,
a packet would have been replicated just to be dropped immediately
after finding a filled LE queue at the respective output port. Such
behavior could be avoided -- for example example, by using a conditional
internal packet replication: a packet would then only be replicated
in case cases where the output link is not fully used. This conditional
replication, however, is probably not widely implemented.

While the resource contention problem caused by multicast packet
replication is also true for other Diffserv PHBs, LE forwarding is
special, because often it is assumed that LE packets only get
forwarded in the case of available resources at the output ports.
The previously mentioned redundancy data traffic could nicely suitably use
the varying available residual bandwidth being utilized the by the LE
PHB, but only if the specific requirements stated above for
conditional replication in the internal implementation of the network
devices are considered.

10. The Update Updates to RFC 4594

[RFC4594] recommended to the use of CS1 as the codepoint in section its
Section 4.10, whereas CS1 was defined in [RFC2474] to have a higher
precedence than CS0, i.e., the default PHB. Consequently, Diffserv
domains implementing CS1 according to [RFC2474] will cause a priority
inversion for LE packets that contradicts with the original purpose of LE.
Therefore, every occurrence of the CS1 DSCP is replaced by the
LE DSCP.

Changes:

o This update to RFC 4594 removes the following entry from figure its
Figure 3:

|---------------+---------+-------------+--------------------------|
| Low-Priority | CS1 | 001000 | Any flow that has no BW |
| Data | | | assurance |
------------------------------------------------------------------

and replaces this by it with the following entry:

|---------------+---------+-------------+--------------------------|
| Low-Priority | LE | 000001 | Any flow that has no BW |
| Data | | | assurance |
------------------------------------------------------------------

o This update to RFC 4594 extends the Notes text below figure Figure 3 that
currently states "Notes for Figure 3: Default Forwarding (DF) and
Class Selector 0 (CS0) provide equivalent behavior and use the
same DS codepoint, '000000'." to state "Notes for Figure 3:
Default Forwarding (DF) and Class Selector 0 (CS0) provide
equivalent behavior and use the same DS codepoint, DSCP, '000000'. The prior
recommendation to use the CS1 DSCP for Low-Priority Data has been
replaced by the current recommendation to use the LE DSCP,
'000001'."
o This update to RFC 4594 removes the following entry from figure its
Figure 4:

|---------------+------+-------------------+---------+--------+----|
| Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes|
| Data | | | | | |
------------------------------------------------------------------

and replaces this by it with the following entry:

|---------------+------+-------------------+---------+--------+----|

|---------------+------+-------------------+----------+--------+----|
| Low-Priority | LE | Not applicable | RFCXXXX RFC 8622 | Rate | Yes|
| Data | | | | | |
------------------------------------------------------------------
-------------------------------------------------------------------

o Section 2.3 of [RFC4594] specifies: specifies the following: "In network
segments that use IP precedence marking, only one of the two
service classes can be supported, High-Throughput Data or
Low-Priority Data. We RECOMMEND that the DSCP value(s) of the
unsupported service class be changed to 000xx1 on ingress and
changed back to original value(s) on egress of the network segment
that uses precedence marking. For example, if Low-Priority Data
is mapped to Standard service class, then 000001 DSCP marking MAY
be used to distinguish it from Standard marked packets on egress."
This document removes this recommendation, because by using the herein defined LE
DSCP defined herein, such remarking re-marking is not necessary. So So, even
if Low-Priority Data is unsupported (i.e., mapped to the default PHB)
PHB), the LE DSCP should be kept across the domain as RECOMMENDED
in Section 8. That removed text is replaced by: by the following: "In
network segments that use IP Precedence marking, the Low-Priority
Data service class receives the same Diffserv QoS as the Standard
service class when the LE DSCP is used for Low-Priority Data
traffic. This is acceptable behavior for the Low-Priority Data
service class, although it is not the preferred behavior."

o This document removes the following line in Section 4.10 of
RFC 4594,
Section 4.10: 4594: "The RECOMMENDED DSCP marking is CS1 (Class
Selector 1)." and replaces this it with the following text:
"The RECOMMENDED DSCP marking is LE (Lower Effort), which replaces
the prior recommendation for CS1 (Class Selector 1) marking."

11. The Update Updates to RFC 8325

Section 4.2.10 of RFC 8325 [RFC8325] specifies that "[RFC3662] and
[RFC4594] both recommend Low-Priority Data be marked CS1 DSCP."
which This
is updated to "[RFC3662] recommends that Low-Priority Data be marked
CS1 DSCP. [RFC4594] [RFC4594], as updated by [RFCXXXX] RFC 8622, recommends Low-
Priority that
Low-Priority Data be marked LE DSCP."
This document removes the following paragraph of RFC 8325, in Section 4.2.10 of
[RFC8325], because this document makes the anticipated change: "Note:
This marking recommendation may change in the future, as [LE-
PHB] [LE-PHB]
defines a Lower Effort (LE) PHB for Low-Priority Data traffic and
recommends an additional DSCP for this traffic."

Section 4.2.10 of RFC 8325 [RFC8325] specifies that "therefore, it is
RECOMMENDED to map Low-Priority Data traffic marked CS1 DSCP to
UP 1" 1", which is updated to "therefore, it is RECOMMENDED to map
Low-Priority Data traffic marked with LE DSCP or legacy CS1 DSCP
to UP 1" 1".

This update to RFC 8325 replaces the following entry from figure its
Figure 1:

+---------------+------+----------+-------------+--------------------+

+---------------+------+----------+------------+--------------------+
| Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) |
| Data | | | | |
+--------------------------------------------------------------------+

by
+-------------------------------------------------------------------+

with the following entries:

+---------------+------+----------+-------------+--------------------+

+---------------+------+----------+------------+--------------------+
| Low-Priority | LE | RFCXXXX RFC 8622 | 1 | AC_BK (Background) |
| Data | | | | |
+--------------------------------------------------------------------+
+-------------------------------------------------------------------+
| Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) |
| Data (legacy) | | | | |
+--------------------------------------------------------------------+
+-------------------------------------------------------------------+

12. The Update to draft-ietf-tsvwg-rtcweb-qos

Section 5 of [I-D.ietf-tsvwg-rtcweb-qos] describes the Recommended
DSCP Values for WebRTC Applications IANA Considerations

This update to [I-D.ietf-tsvwg-rtcweb-qos] replaces all occurrences
of CS1 with LE in Table 1:

+------------------------+-------+------+-------------+-------------+
| Flow Type | Very | Low | Medium | High |
| | Low | | | |
+------------------------+-------+------+-------------+-------------+
| Audio | LE | DF | EF (46) | EF (46) |
| | (1) | (0) | | |
| | | | | |
| Interactive Video with | document assigns the Differentiated Services Field Codepoint
(DSCP) '000001' from the "Differentiated Services Field Codepoints
(DSCP)" registry (https://www.iana.org/assignments/dscp-registry/)
("DSCP Pool 3 Codepoints", Codepoint Space xxxx01, Standards Action)
[RFC8126] to the LE | DF | AF42, AF43 | AF41, AF42 |
| or without Audio | (1) | (0) | (36, 38) | (34, 36) |
| | | | | |
| Non-Interactive Video | PHB. This document uses a DSCP from Pool 3 in
order to avoid problems for other PHB-marked flows, where they could
become accidentally re-marked as LE | DF | AF32, AF33 | AF31, AF32 |
| with or without Audio | (1) | (0) | (28, 30) | (26, 28) |
| | | | | |
| Data | PHB, e.g., due to partial DSCP
bleaching. See [RFC8436] regarding reclassifying Pool 3 for
Standards Action.

IANA has updated this registry as follows:

o Name: LE | DF | AF11 | AF21 |
| | (1) | (0) | | |
+------------------------+-------+------+-------------+-------------+

and updates the following paragraph:

"The above table assumes that packets marked with CS1

o Value (Binary): 000001

o Value (Decimal): 1

o Reference: RFC 8622

13. Security Considerations

There are treated as
"less than best effort", such no specific security exposures for this PHB. Since it
defines a new class that is of low forwarding priority, re-marking
other traffic as the LE behavior described in
[RFC3662]. However, the treatment traffic may lead to QoS degradation of CS1 such
traffic. Thus, any attacker that is implementation
dependent. If an implementation treats CS1 as other than "less than
best effort", then the actual priority (or, more precisely, able to modify the per-
hop-behavior) DSCP of the packets may be changed from what is intended.
It is common for CS1 a
packet to be treated LE may carry out a downgrade attack. See the same as DF, so applications
and browsers using CS1 cannot assume that CS1 will be treated
differently than DF [RFC7657]. However, it is also possible per general
security considerations in [RFC2474] for CS1 traffic to be given better treatment than DF, thus
caution should be exercised when electing and [RFC2475].

With respect to privacy, an attacker could use CS1. This the information from
the DSCP to infer that the transferred (probably even encrypted)
content is one considered of low priority or low urgency by a user if the cases where marking packets using these recommendations can make
things worse."

as follows:

"The above table assumes that packets marked with LE are treated as
lower effort (i.e., "less than best effort"), such as
DSCP was set per the LE behavior
described in [RFCXXXX]. However, user's request. On the treatment of LE one hand, this disclosed
information is
implementation dependent. If an implementation treats LE useful only if correlation with metadata (such as other
than "less than best effort", then the actual priority (or, more
precisely,
user's IP address) and/or other flows reveal a user's identity. On
the per- hop-behavior) of other hand, it might help an observer (e.g., a state-level actor)
who is interested in learning about the packets user's behavior from observed
traffic: LE-marked background traffic (such as software downloads,
operating system updates, or telemetry data) may be changed from
what is intended. It is common less interesting
for surveillance than general web traffic. Therefore, the LE marking
may help the observer to be treated focus on potentially more interesting
traffic (however, the same as DF,
so applications and browsers using LE cannot assume that LE will be
treated differently than DF [RFC7657]. During development of user may exploit this
document, the CS1 DSCP was recommended for "very low" application
priority traffic; implementations that followed that recommendation
SHOULD be updated to use particular assumption and
deliberately hide interesting traffic in the LE DSCP instead of the CS1 DSCP."

13. IANA Considerations

This document assigns the Differentiated Services Field Codepoint
(DSCP) '000001' aggregate). Apart
from such considerations, the Differentiated Services Field Codepoints
(DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp-
registry.xhtml) (Pool 3, Codepoint Space xxxx01, Standards Action) to impact of disclosed information by the
LE PHB. This document suggests to use a DSCP from Pool 3 in
order to avoid problems for other PHB marked flows to become
accidentally remarked as LE PHB, e.g., due to partial DSCP bleaching.
See [RFC8436] for re-classifying Pool 3 for Standards Action.

IANA is requested to update likely negligible in most cases, given the registry as follows:

o Name: LE

o Value (Binary): 000001

o Value (Decimal): 1

o Reference: [RFC number of this memo]

14. Security Considerations

There are no specific security exposures for this PHB. Since it
defines a new class of low forwarding priority, remarking other
traffic as LE numerous
traffic may lead to quality-of-service degradation of
such traffic. Thus, any attacker that is able to modify the DSCP of
a packet to LE may carry out a downgrade attack. See the analysis possibilities and general
security considerations privacy threats (e.g., see
[RFC6973]).

14. References

14.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2474] Nichols, K., Blake, S., Baker, F., and [RFC2475].

With respect to privacy, an attacker could use the information from
the DSCP to infer that the transferred (probably even encrypted)
content is considered of low priority or low urgency by a user, in
case the DSCP was set on the user's request. On the one hand, this
disclosed information is useful only if correlation with metadata
(such as the user's IP address) and/or other flows reveal user
identity. On the other hand, it might help an observer (e.g., a
state level actor) who is interested in learning about the user's
behavior from observed traffic: LE marked background traffic (such as
software downloads, operating system updates, or telemetry data) may
be less interesting for surveillance than general web traffic.
Therefore, the LE marking may help the observer to focus on
potentially more interesting traffic (however, the user may exploit
this particular assumption and deliberately hide interesting traffic
in the LE aggregate). Apart from such considerations, the impact of
disclosed information by the LE DSCP is likely negligible in most
cases given the numerous traffic analysis possibilities and general
privacy threats (e.g., see [RFC6973]).

15. References

15.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>.
<https://www.rfc-editor.org/info/rfc2474>.

[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<http://www.rfc-editor.org/info/rfc2475>.
<https://www.rfc-editor.org/info/rfc2475>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174,
DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.

15.2.

14.2. Informative References

[carlberg-lbe-2001]

[Carlberg-LBE-2001]
Carlberg, K., Gevros, P., and J. Crowcroft, "Lower than
best effort: a design and implementation", ACM SIGCOMM
Computer Communications Review Communication Review, Volume 31, 31 Issue 2
supplement, DOI 10.1145/844193.844208, April 2001,
<https://doi.org/10.1145/844193.844208>.

[chown-lbe-2003]
<https://dl.acm.org/citation.cfm?doid=844193.844208>.

[Chown-LBE-2003]
Chown, T., Ferrari, T., Leinen, S., Sabatino, R., Simar,
N., and S. Venaas, "Less than Best Effort: Application
Scenarios and Experimental Results", In Proceedings of the
Second International Workshop on Quality of Service in
Multiservice IP Networks (QoS-IP 2003), Lecture Notes in
Computer Science, vol 2601. 2601, Springer, Berlin,
Heidelberg Heidelberg,
Pages 131-144, DOI 10.1007/3-540-36480-3_10,
February 2003,
<https://doi.org/10.1007/3-540-36480-3_10>.

[draft-bless-diffserv-lbe-phb-00] <https://link.springer.com/chapter/
10.1007%2F3-540-36480-3_10>.

[Diffserv-LBE-PHB]
Bless, R. and K. Wehrle, "A Lower Than Best-Effort
Per-Hop Behavior", draft-bless-diffserv-lbe-phb-00 (work Work in
progress), Progress,
draft-bless-diffserv-lbe-phb-00, September 1999, <https://tools.ietf.org/html/
draft-bless-diffserv-lbe-phb-00>.

[I-D.ietf-tsvwg-rtcweb-qos]
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.

[ietf99-secchi] 1999.

[IETF99-Secchi]
Secchi, R., Venne, A., and A. Custura, "Measurements
concerning the DSCP for a LE PHB", Presentation held at
the 99th IETF Meeting, TSVWG, Prague , Prague, July 2017,
<https://datatracker.ietf.org/meeting/99/materials/slides-
99-tsvwg-sessb-31measurements-concerning-the-dscp-for-a-
le-phb-00>.
<https://datatracker.ietf.org/meeting/99/materials/
slides-99-tsvwg-sessb-31measurements-concerning-
the-dscp-for-a-le-phb-00>.

[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>.

[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
<https://www.rfc-editor.org/info/rfc3168>.

[RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural
Guidelines and Philosophy", RFC 3439,
DOI 10.17487/RFC3439, December 2002,
<https://www.rfc-editor.org/info/rfc3439>.

[RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
Per-Domain Behavior (PDB) for Differentiated Services",
RFC 3662, DOI 10.17487/RFC3662, December 2003,
<http://www.rfc-editor.org/info/rfc3662>.
<https://www.rfc-editor.org/info/rfc3662>.

[RFC3754] Bless, R. and K. Wehrle, "IP Multicast in Differentiated
Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754,
April 2004, <http://www.rfc-editor.org/info/rfc3754>. <https://www.rfc-editor.org/info/rfc3754>.

[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<http://www.rfc-editor.org/info/rfc4594>.
<https://www.rfc-editor.org/info/rfc4594>.

[RFC5053] Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer,
"Raptor Forward Error Correction Scheme for Object
Delivery", RFC 5053, DOI 10.17487/RFC5053, October 2007,
<https://www.rfc-editor.org/info/rfc5053>.

[RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort
Transport Protocols", RFC 6297, DOI 10.17487/RFC6297,
June 2011, <http://www.rfc-editor.org/info/rfc6297>. <https://www.rfc-editor.org/info/rfc6297>.

[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
"Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
DOI 10.17487/RFC6817, December 2012,
<http://www.rfc-editor.org/info/rfc6817>.
<https://www.rfc-editor.org/info/rfc6817>.

[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.

[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.

[RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using
Explicit Congestion Notification (ECN)", RFC 8087,
DOI 10.17487/RFC8087, March 2017,
<https://www.rfc-editor.org/info/rfc8087>.

[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <http://www.rfc-editor.org/info/rfc8100>.

[RFC8325] Szigeti, T., Henry, J., <https://www.rfc-editor.org/info/rfc8100>.

[RFC8126] Cotton, M., Leiba, B., and F. Baker, "Mapping Diffserv to
IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February
2018, <https://www.rfc-editor.org/info/rfc8325>.

[RFC8436] Fairhurst, G., "Update to IANA Registration Procedures for
Pool 3 Values in the Differentiated Services Field
Codepoints (DSCP) Registry", RFC 8436,
DOI 10.17487/RFC8436, August 2018,
<https://www.rfc-editor.org/info/rfc8436>.

Appendix A. History of the LE PHB

A first version of this PHB was suggested by Roland Bless and Klaus
Wehrle in September 1999 [draft-bless-diffserv-lbe-phb-00], named "A
Lower Than Best-Effort Per-Hop Behavior". After some discussion in
the Diffserv Working Group Brian Carpenter and Kathie Nichols
proposed a "bulk handling" per-domain behavior and believed a PHB was
not necessary. Eventually, "Lower Effort" was specified as per-
domain behavior and finally became [RFC3662]. More detailed
information about its history can be found in Section 10 of
[RFC3662].

There are several other names in use for this type of PHB or
associated service classes. Well-known is the QBone Scavenger
Service (QBSS) that was proposed in March 2001 within the Internet2
QoS Working Group. Alternative names are "Lower-than-best-effort"
[carlberg-lbe-2001] or "Less-than-best-effort" [chown-lbe-2003].

Appendix B. Acknowledgments

Since text is partially borrowed from earlier Internet-Drafts and
RFCs the co-authors of previous specifications are acknowledged here:
Kathie Nichols and Klaus Wehrle. David Black, Olivier Bonaventure,
Spencer Dawkins, Toerless Eckert, Gorry Fairhurst, Ruediger Geib, and
Kyle Rose provided helpful comments and (partially also text)
suggestions.

Appendix C. Change History

This section briefly lists changes between Internet-Draft versions
for convenience.

Changes in Version 10: (incorporated comments from IESG discussion as
follows)

o Appended "for Differentiated Services" to the title as suggested
by Alexey.

o Addressed Deborah Brungard's discuss: changed phrase to "However,
non-LE traffic (e.g., BE traffic) SHOULD NOT be remarked to LE."
with additional explanation as suggested by Gorry.

o Fixed the sentence "An LE PHB SHOULD NOT be used for a customer's
"normal Internet" traffic nor should packets be "downgraded" to
the LE PHB instead of being dropped, particularly when the packets
are unauthorized traffic." according to Alice's and Mirja's
comments.

o Made reference to RFC8174 normative.

o Added hint for the RFC editor to apply changes from section
Section 12 and to delete it afterwards.

o Incorporated Mirja's and Benjamin's suggestions.

o Editorial suggested by Gorry: In case => In the case that

Changes in Version 09:

o Incorporated comments from IETF Last Call:

* from Olivier Bonaventure: added a bit of text for session
resumption and congestion control aspects as well as ECN usage.

* from Kyle Rose: Revised privacy considerations text in Security
Considerations Section

Changes in Version 08:

o revised two sentences as suggested by Spencer Dawkins

Changes in Version 07:

o revised some text for clarification according to comments from
Spencer Dawkins

Changes in Version 06:

o added Multicast Considerations section with input from Toerless
Eckert

o incorporated suggestions by David Black with respect to better
reflect legacy CS1 handling

Changes in Version 05:

o added scavenger service class into abstract

o added some more history

o added reference for "Myth of Over-Provisioning" in RFC3439 and
references to presentations w.r.t. codepoint choices

o added text to update draft-ietf-tsvwg-rtcweb-qos

o revised text on congestion control in case of remarking to BE

o added reference to DSCP measurement talk @IETF99

o small typo fixes
Changes in Version 04:

o Several editorial changes according to review from Gorry Fairhurst

o Changed the section structure a bit (moved subsections 1.1 and 1.2
into own sections 3 and 7 respectively)

o updated section 2 on requirements language

o added updates to RFC 8325

o tried to be more explicit what changes are required to RFCs 4594
and 8325

Changes in Version 03:

o Changed recommended codepoint to 000001

o Added text to explain the reasons for the DSCP choice

o Removed LE-min,LE-strict discussion

o Added one more potential use case: reporting errors or telemetry
data from OSs

o Added privacy considerations to the security section (not worth an
own section I think)

o Changed IANA considerations section

Changes in Version 02:

o Applied many editorial suggestions from David Black

o Added Multicast traffic use case

o Clarified what is required for deployment in section 1.2
(Deployment Considerations)

o Added text about implementations using AQMs and ECN usage

o Updated IANA section according to David Black's suggestions

o Revised text in the security section

o Changed copyright Notice to pre5378Trust200902

Changes in Version 01:

o Now obsoletes RFC 3662.

o Tried to be more precise in section 1.1 (Applicability) according
to R. Geib's suggestions, so rephrased several paragraphs. Added
text about congestion control

o Change section 2 (PHB Description) according to R. Geib's
suggestions.

o Added RFC 2119 language to several sentences.

o Detailed the description of remarking implications and
recommendations in Section 8.

o Added T. Narten, "Guidelines for
Writing an IANA Considerations Section 10 to explicitly list changes with respect to in RFCs", BCP 26,
RFC
4594, because this document will update it.

Appendix D. Note 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to
IEEE 802.11", RFC Editor

This section lists actions 8325, DOI 10.17487/RFC8325,
February 2018, <https://www.rfc-editor.org/info/rfc8325>.

[RFC8436] Fairhurst, G., "Update to IANA Registration Procedures for
Pool 3 Values in the Differentiated Services Field
Codepoints (DSCP) Registry", RFC editor during final
formatting.

o Apply 8436,
DOI 10.17487/RFC8436, August 2018,
<https://www.rfc-editor.org/info/rfc8436>.

Appendix A. History of the suggested changes LE PHB

A first draft version of section Section 12 this PHB was suggested by Roland Bless and add a
normative reference
Klaus Wehrle in September 1999 [Diffserv-LBE-PHB], named "A Lower
Than Best-Effort Per-Hop Behavior". After some discussion in draft-ietf-tsvwg-rtcweb-qos to this RFC.

o Delete Section 12.

o Please replace the occurrences of RFCXXXX
Diffserv Working Group, Brian Carpenter and Kathie Nichols proposed a
"bulk handling" per-domain behavior and believed a PHB was not
necessary. Eventually, "Lower Effort" was specified as per-domain
behavior and finally became [RFC3662]. More detailed information
about its history can be found in Section 10 and
Section 11 with the assigned RFC number of [RFC3662].

There are several other names in use for this document.

o Delete Appendix C.

o Delete this section. type of PHB or
associated service classes. Well known is the QBone Scavenger
Service (QBSS) that was proposed in March 2001 within the Internet2
QoS Working Group. Alternative names are "Lower than best effort"
[Carlberg-LBE-2001] or "Less than best effort" [Chown-LBE-2003].

Acknowledgments

Since text is partially borrowed from earlier Internet-Drafts and
RFCs, the coauthors of previous specifications are acknowledged here:
Kathie Nichols and Klaus Wehrle. David Black, Olivier Bonaventure,
Spencer Dawkins, Toerless Eckert, Gorry Fairhurst, Ruediger Geib, and
Kyle Rose provided helpful comments and (partially also text)
suggestions.

Author's Address

Roland Bless
Karlsruhe Institute of Technology (KIT)
Institute of Telematics (TM)
Kaiserstr. 12
Karlsruhe 76131
Germany

Phone: +49 721 608 46413
Email: roland.bless@kit.edu