wdiff rfc7555v4.txt rfc7555.txt

Internet Engineering Task Force (IETF) G. Swallow
Request for Comments: 7555 V. Lim
Category: Standards Track Cisco Systems
ISSN: 2070-1721 S. Aldrin
Huawei Technologies
May
June 2015

Proxy MPLS Echo Request

Abstract

This document defines a means of remotely initiating Multiprotocol
Label Switched Protocol (MPLS) Pings on Label Switched Paths. An
MPLS Proxy Ping Request is sent to any Label Switching Router along a
Label Switched Path. The primary motivations for this facility are
first to limit the number of messages and related processing when
using LSP Ping in large Point-to-Multipoint LSPs, and second to
enable tracing from leaf to leaf (or root).

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7555.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction ....................................................3
1.1. Requirements Language ......................................4
1.2. Terminology ................................................5
2. Proxy Ping Overview .............................................5
2.1. Initiating Proxy Ping ......................................6
2.2. Handling at Proxy LSR ......................................6
2.2.1. Backward Compatibility ..............................6
3. Proxy MPLS Echo Request/Reply Procedures ........................7
3.1. Procedures for the Initiator ...............................7
3.2. Procedures for the Proxy LSR ...............................8 ...............................9
3.2.2. Downstream Detailed Maps and Downstream
Maps in Proxy Reply ................................12
3.2.3. Sending an MPLS Proxy Ping Reply ...................12
3.2.4. Sending the MPLS Echo Requests .....................12 .....................13
3.2.4.1. Forming the Base MPLS Echo Request ........12 ........13
3.2.4.2. Per-Interface Sending Procedures ..........14
4. Proxy Ping Request/Reply Messages ..............................15
4.1. Proxy Ping Request/Reply Message Formats ..................15
4.2. Proxy Ping Request Message Contents .......................15
4.3. Proxy Ping Reply Message Contents .........................16
5. TLV Formats ....................................................16
5.1. Proxy Echo Parameters TLV .................................16
5.1.1. Next Hop Sub-TLV ...................................20
5.2. Reply-to Address TLV ......................................21
5.3. Upstream Neighbor Address TLV .............................21
5.4. Downstream Neighbor Address TLV ...........................22
6. Security Considerations ........................................23
7. IANA Considerations ............................................24
7.1. Proxy Echo Parameters Sub-TLVs ............................24
7.2. Proxy Flags ...............................................25
7.3. Downstream Address Mapping Registry .......................25
7.4. Next Hop Sub-TLV Address Type Registry ....................25
8. References .....................................................26
8.1. Normative References ......................................26
8.2. Informative References ....................................27
Acknowledgements ..................................................27
Authors' Addresses ................................................28

1. Introduction

This document is motivated by two broad issues in connection with
diagnosing Point-to-Multipoint (P2MP) Label Switched Paths (LSPs).
The first is scalability due to the automatic replication of
Multiprotocol Label Switching (MPLS) Echo Request messages as they
proceed down the tree. The second, which is primarily motivated by
LDP-based P2MP and Multipoint-to-Multipoint (MP2MP) LSPs [RFC6388],
is the ability to trace a sub-LSP from leaf node to root node.

When tracing from a source to a particular leaf in a P2MP or MP2MP
tree, nodes not along that path will need to process MPLS Echo
Request messages that are received. The number of MPLS Echo Replies
sent in response to an MPLS Echo Request quickly multiplies, as the
Label Switching Routers (LSRs), which are part of the tree but not
along the path of the trace, could be responding to the received MPLS
Echo Request as well. This could also overwhelm the source to
process all the MPLS Echo Reply messages it receives. It is
anticipated that many of the applications for P2MP/MP2MP tunnels will
require OAM that is both rigorous and scalable.

Suppose one wishes to trace a P2MP LSP to localize a fault that is
affecting one egress or a set of egresses. Suppose one follows the
normal procedure for tracing -- namely, repeatedly pinging from the
root, incrementing the Time to Live (TTL) by one after each three or
so pings. Such a procedure has the potential for producing a large
amount of processing at the P2MP-LSP midpoints and egresses. It also
could produce an unwieldy number of replies back to the root.

One alternative would be to begin sending pings from points at or
near the affected egress(es) and then work backwards toward the root.
The TTL could be held constant (say, two), limiting the number of
responses to the number of next-next-hops of the point where a ping
is initiated.

In the case of Resource Reservation Protocol Traffic Engineering
(RSVP-TE), all setup is initiated from the root of the tree. Thus,
the root of the tree has knowledge of all the leaf nodes and usually
the topology of the entire tree. Thus, the above alternative can
easily be initiated by the root node.

In [RFC6388], the situation is quite different. Leaf nodes initiate
connectivity to the tree, which is granted by the first node toward
the root that is part of the tree. The root node may only be aware
of the immediately adjacent (downstream) nodes of the tree.
Initially, the leaf node only has knowledge of the (upstream) node to
which it is immediately adjacent. However, this is sufficient
information to initiate a trace. First, the above procedure is
applied by asking that node to ping across the final link. That is,
a message is sent from the leaf to the upstream node requesting it to
send an MPLS Echo Request for the Forward Equivalence Class (FEC) of
the tree in question on said link. The leaf node also requests the
identity of the upstream neighbor's upstream neighbor for that FEC.
With this information, the procedure can iteratively be applied until
the fault is localized or the root node is reached. In all cases,
the TTL for the request need only be at most 2. Thus, the processing
load of each request is small, since only a limited number of nodes
will receive the request.

This document defines protocol extensions to MPLS ping [RFC4379] to
allow a third party to remotely cause an MPLS Echo Request message to
be sent down an LSP or part of an LSP. The procedure described in
the paragraphs above does require that the initiator know the
previous-hop node to the one which was pinged on the prior iteration.
This information is readily available in [RFC4875]. This document
also provides a means for obtaining this information for P2MP and
MP2MP LSPs that are set up with LDP as described in [RFC6388].

While the motivation for this document came from multicast scaling
concerns, its applicability may be wider. The procedures presented
in this document are applicable to all LSP Ping FEC types where the
MPLS Echo Request/Reply are IP encapsulated and the MPLS Echo Reply
can be sent out of band of the LSP over IP. Remote pinging of LSPs
that involves the use of in-band control channels is beyond the scope
of this document.

Other uses of this facility are beyond the scope of this document.
In particular, the procedures defined in this document only allow
testing of a FEC stack consisting of a single FEC. The procedures
also do not allow the initiator to specify the label assigned to that
FEC, nor do the procedures allow the initiator to cause any
additional labels to be added to the label stack of the actual MPLS
Echo Request message.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

The term "Must Be Zero" (MBZ) is used in TLV descriptions for
reserved fields. These fields MUST be set to zero when sent and
ignored on receipt.

Based on context, the terms "leaf" and "egress" are used
interchangeably. "Egress" is used where consistency with [RFC4379]
was deemed appropriate. "Receiver" is used in the context of
receiving protocol messages.

1.2. Terminology

Term Definition
----- -------------------------------------------
LSP Label Switched Path
LSR Label Switching Router
mLDP Multipoint LDP
MP2MP Multipoint to Multipoint
MTU Maximum Transmission Unit
P2MP Point to Multipoint
TTL Time to Live

2. Proxy Ping Overview

This document defines a protocol interaction between a first LSR and
another LSR that is part of an LSP in order to allow the first LSR to
request that the second LSR initiate an LSP Ping for the LSP on the
first LSR's behalf. Since the second LSR sends the LSP Ping on
behalf of the first LSR, it does not maintain state to be able to
handle the corresponding LSP Ping response. Instead, the responder
to the LSP Ping sends the LSP Ping response to either the first LSR
or another LSR configured to handle it. Two new LSP Ping messages
are defined for remote pinging: the MPLS Proxy Ping Request and the
MPLS Proxy Ping Reply.

A remote ping operation on a P2MP LSP generally involves at least
three LSRs; in some scenarios, none of these are the ingress (root)
or an egress (leaf) of the LSP.

We refer to these LSRs with the following terms:

Initiator - the LSR that initiates the ping operation by sending
an MPLS Proxy Ping Request message

Proxy LSR - the LSR that is the destination of the MPLS Proxy Ping
Request message and the potential initiator of the MPLS Echo
Request

Receiver(s) - the LSR(s) that receive the MPLS Echo Request
message

Responder - A receiver that responds to an MPLS Proxy Ping Request
or an MPLS Echo Request
We note that in some scenarios, the initiator could also be the
responder; in that case, the response would be internal to the LSR.

2.1. Initiating Proxy Ping

The initiator formats an MPLS Proxy Ping Request message and sends it
to the Proxy LSR, an LSR it believes to be on the path of the LSP.
This message instructs the Proxy LSR either to reply with Proxy
information or to send an MPLS Echo Request in-band of the LSP. The
initiator requests Proxy information so that it can learn additional
information it needs to use to form a subsequent MPLS Proxy Ping
Request. For example, during LSP traceroute, an initiator needs the
downstream map information to form an MPLS Echo Request. An
initiator may also want to learn a Proxy LSR's FEC neighbor
information so that it can form Proxy Ping Requests to various LSRs
along the LSP.

2.2. Handling at Proxy LSR

The Proxy LSR either replies with the requested Proxy information or
validates that it has a label mapping for the specified FEC and that
it is authorized to send the specified MPLS Echo Request on behalf of
the initiator.

If the Proxy LSR has a label mapping for the FEC and all
authorization checks have passed, the Proxy LSR formats an MPLS Echo
Request. If the source address of the MPLS Echo Request is not set
to the Proxy Request source address, the initiator MUST include a
Reply-to Address TLV containing the source address to use in the MPLS
Echo Request. It then sends the MPLS Echo Request in-band of the
LSP.

The receivers process the MPLS Echo Request as normal, sending their
MPLS Echo Replies back to the initiator.

If the Proxy LSR failed to send an MPLS Echo Request as normal
because it encountered an issue while attempting to send, an MPLS
Proxy Ping Reply message is sent back with a Return Code indicating
that the MPLS Echo Request could not be sent.

2.2.1. Backward Compatibility

As described in Section 4.4 of [RFC4379], if the packet is not well-
formed, LSR X SHOULD send an MPLS Echo Reply with the Return Code set
to "Malformed echo request received" and the Return Subcode to zero.
If there are any TLVs not marked as "Ignore" that the Proxy LSR does
not understand, the Proxy LSR SHOULD send an MPLS "TLV not
understood" (as appropriate), and the Return Subcode is set to zero.

In the case where the targeted Proxy LSR does not understand the LSP
Ping Echo Request at all, like any other LSR that does not understand
the messages, it MUST drop the message and MUST NOT send any message
back to the initiator.

3. Proxy MPLS Echo Request/Reply Procedures

3.1. Procedures for the Initiator

The initiator creates an MPLS Proxy Ping request message.

The message MUST contain a Target FEC Stack that describes the FEC
being tested. The topmost FEC in the target FEC stack is used at the
Proxy LSR to look up the MPLS label stack that will be used to
encapsulate the MPLS Echo Request packet.

The MPLS Proxy Ping Request message MUST contain a Proxy Echo
Parameters TLV. In that TLV, the address type is set to either IPv4
or IPv6. The Destination IP Address is set to the value to be used
by the Proxy LSR to build the MPLS Echo Request packet. The MPLS
Echo Request IP header destination address is as specified in
[RFC4379]. If the Address Type is IPv4, it MUST be an address is
from the range 127/8; if the Address Type is IPv6, MUST be an address
from the range ::ffff:7f00:0/104.

The Reply Mode and Global Flags of the Proxy Echo Parameters TLV are
set to the values to be used in the MPLS Echo Request message header.
The Source UDP Port is set to the value to be used in the MPLS Echo
Request (the source port is supplied by the Proxy Ping initiator
because it or an LSR known to it handles the LSP Ping responses).
The TTL is set to the value to be used in the outgoing MPLS label
stack. See Section 5.1 for further details.

If the FEC's Upstream/Downstream Neighbor address information is
required, the initiator sets the "Request for FEC neighbor
information" Proxy Flags in the Proxy Echo Parameters TLV.

If a Downstream Detailed Mapping TLV (or Downstream Mapping TLV,
which is deprecated) is required in an MPLS Proxy Ping Reply, the
initiator sets the "Request for Downstream Detailed Mapping" (or
"Request for Downstream Mapping") Proxy Flag in the Proxy Echo
Parameters TLV. Only one of the two flags can be set.

The Proxy Request Reply Mode is set with one of the Reply Modes
defined in [RFC4379] as appropriate.

A list of next-hop IP addresses MAY be included to limit the next
hops towards which the MPLS Echo Request message will be sent. These
are encoded as Next Hop sub-TLVs and included in the Proxy Echo
Parameters TLV.

Although not explicitly spelled out in [RFC4379], LSP Ping packets
can be formed to a desired size using a Pad TLV and then used to test
the Maximum Transmission Unit (MTU) of an LSP. When testing an LSP's
MTU, if the message is transported as an IP datagram, the IP header
DF bit MUST be set to prevent IP fragmentation by the IP forwarding
layer. The Proxy Echo Parameter TLV MPLS Payload Size field is
defined for this purpose and may be set to request that the MPLS Echo
Request (including any IP and UDP header) be zero-padded to the
specified size. When a non-zero MPLS payload size is specified, the
Proxy LSR introduces a Pad TLV to build the MPLS Echo Request packet,
so in this case, the Proxy Ping Request MUST NOT include a Pad TLV.

Any of following TLVs MAY be included. These TLVs are used to form
the MPLS Echo Request messages by the Proxy LSR:

Pad

Vendor Enterprise Number

Reply TOS Byte

P2MP Responder Identifier [RFC6425]

Echo Jitter [RFC6425]

Vendor Private TLVs

Downstream Detailed Mapping (DDMAP) or Downstream Mapping (DSMAP)
TLVs MAY be included. These TLVs will be matched to the next-hop
address for inclusion in those particular MPLS Echo Request messages.

The message is then encapsulated in a UDP packet. The source UDP
port for the MPLS Proxy Ping Request message is chosen by the
initiator; the destination UDP port is set to 3503. The IP header is
set as follows: the source IP address is a routable address of the
initiator; the destination IP address is a routable address to the
Proxy LSR. The packet is then sent with the IP TTL set to 255.

3.2. Procedures for the Proxy LSR

A Proxy LSR that receives an MPLS Proxy Ping Request message parses
the packet to ensure that it is a well-formed packet. It checks that
the TLVs that are not marked "Ignore" are understood. If any part of
the message is malformed, it sets the Return Code to "Malformed echo
request received". If all the TLVs are well-formed and any TLVs are
not understood, the Return Code is set to "TLV not understood". The
Return Subcode is set to zero for both cases.

If the Reply Mode of the message header is not 1 ("Do not reply"), an
MPLS Proxy Ping Reply message SHOULD be sent as described below.

If the Return Code is "TLV not understood", no more processing of the
MPLS Proxy Ping Request message is required. The Proxy LSR sends an
MPLS Proxy Ping Reply message with an Errored TLVs TLV containing
(only) the TLVs that were not understood.

The MPLS Proxy Ping Request is expected to be transported to the
Proxy LSR via IP forwarding mechanisms instead of using the same
techniques that are employed to inject an MPLS Echo Request packet
into an LSP. The MPLS Echo Request would use IP TTL, MPLS TTL,
and/or loopback addresses (IPv4 127.x.x.x or IPv6 ::ffff:7f00/104) in
the IP header destination address field to trigger the packet to be
handled via an LSR's forwarding exception processing path. The Proxy
LSR MUST check whether or not MPLS Proxy Ping Request packets arrive
via exception path. Packets arriving via IP TTL expiry, IP
destination address set to a loopback address, or label TTL expiry
MUST be treated as "Unauthorized" packets. An MPLS Proxy Ping Reply
message MAY be sent with a Return Code of 16, "Proxy Ping not
authorized".

The header fields Sender's Handle and Sequence Number are not
examined, but they are included in the MPLS Proxy Ping Reply or MPLS
Echo Request message, if either is sent as a direct result of the
received message.

The Proxy LSR validates that it has a label mapping for the specified
FEC, determines if it is an ingress, egress, transit or bud node, and
then sets the Return Code as appropriate. A new Return Code of 19,
"Replying router has FEC mapping for topmost FEC", has been defined
for the case where the Proxy LSR is an ingress (for example, the head
of the TE tunnel or a transit router) because the existing Return
Codes defined by RFC 4379 don't match the situation. For example,
when a Proxy LSR is a transit router, it's not appropriate for the
Return Code to describe how the packet would transit because the MPLS
Proxy Ping Request doesn't contain information about what input
interface the MPLS Echo Request would be switched from at the Proxy
LSR.

The Proxy LSR then determines if it is authorized to send the
specified MPLS Echo Request on behalf of the initiator. A Proxy LSR
MUST be capable of filtering addresses to validate initiators. Other
filters on FECs or MPLS Echo Request contents MAY be applied. If a
configured filter has been invoked and an address does not pass the
filter, then an MPLS Echo Request message MUST NOT be sent, and the
event SHOULD be logged. An MPLS Proxy Ping Reply message MAY be sent
with a Return Code of 16, "Proxy Ping not authorized".

The destination address specified in the Proxy Echo Parameters TLV is
checked to ensure that it conforms to the allowed IPv4 or IPv6
address range. If not, the Return Code is set to "Malformed echo
request received" and the Return Subcode is set to zero. If the
Reply Mode of the message header is not 1, an MPLS Proxy Ping Reply
message SHOULD be sent as described below.

The TTL specified in the Proxy Echo Parameters TLV is checked to
ensure it contains a value in the range [1,255]. If not, the Return
Code MUST be set to 17, "Proxy Ping parameters need to be modified".
If the Reply Mode of the message header is not 1, an MPLS Proxy Ping
Reply message SHOULD be sent as described below.

If the "Request for FEC Neighbor Address info" flag is set, the
Upstream Neighbor Address and Downstream Neighbor Address TLVs are
formatted for inclusion in the MPLS Proxy Ping reply. If the
Upstream or Downstream address is unknown, the corresponding TLV is
omitted.

If there are Next Hop sub-TLVs in the Proxy Echo Parameters TLV, each
address is examined to determine if it is a valid next hop for this
FEC. If any are not, the Proxy Echo Parameters TLV SHOULD be updated
to remove unrecognized Next Hop sub-TLVs. The updated Proxy Echo
Parameters TLV MUST be included in the MPLS Proxy Ping Reply.

If the "Request for Downstream Detailed Mapping" or "Request for
Downstream Mapping" flag is set, the Proxy LSR formats (for inclusion
in the MPLS Proxy Ping Reply) a DS/DDMAP TLV for each interface over
which the MPLS Echo Request will be sent.

If the Proxy LSR is the egress for the FEC, the behavior of the Proxy
LSR varies depending on whether the LSR is an egress of a P2P LSP, a
P2MP LSP, or MP2MP LSP. Additional details can be found in Section
3.2.1, "Proxy LSR Handling When It Is Egress for FEC".

If the Reply Mode of the MPLS Proxy Ping Request message header is 1
("Do not reply"), no MPLS Proxy Ping Reply is sent. Otherwise, an
MPLS Proxy Ping Reply message or MPLS Echo Request SHOULD be sent as
described below.

3.2.1. Proxy LSR Handling When It Is Egress for FEC

This section describes the different behaviors for the Proxy LSR when
it's the egress for the FEC. In the P2MP bud node and MP2MP bud node
egress cases, different behavior is required.

In the case where an MPLS Echo Request is originated by an LSR that
is a bud or egress node of a P2MP/MP2MP, MPLS Echo Replies are
returned from downstream/upstream LSRs and will not include an MPLS
Echo Reply from the LSR that originated the MPLS Echo Request. This
section describes the behavior required at a bud or egress node to
return or not return information from MPLS Echo Replies in the Proxy
Echo Reply so that no changes are required in implementations that
are compliant with [RFC4379]. The Proxy Initiator should receive the
same MPLS Echo Replies as in the case of the originator of the LSP
Ping; any additional information (such as the Proxy LSR being a bud
or egress node) is returned in the MPLS Proxy Ping Reply.

When the Proxy LSR is the egress of a P2P FEC, an MPLS Proxy Ping
Reply SHOULD be sent to the initiator with the Return Code set to 3,
"Replying router is an egress for the FEC at stack-depth", with
Return Subcode set to zero.

When the Proxy LSR is the egress of a P2MP FEC, it can be either a
bud node or just an egress. If the Proxy LSR is a bud node, an MPLS
Proxy Ping Reply SHOULD be sent to the initiator with the return code
set to 3, "Replying router is an egress for the FEC at stack-depth",
and Return Subcode set to zero. DS/DDMAPs are included only if the
Proxy Initiator requested information be returned in an MPLS Proxy
Ping Reply. If the Proxy LSR is a bud node but there has not been a
request to return an MPLS Proxy Ping Reply, the Proxy LSR SHOULD send
MPLS Echo Request packet(s) to the downstream neighbors (no MPLS Echo
Reply is sent to the Proxy Initiator to indicate that the Proxy LSR
is an egress). If the Proxy LSR is just an egress, an MPLS Proxy
Ping Reply SHOULD be sent to the initiator with the Return Code set
to 3, "Replying router is an egress for the FEC at stack-depth", and
Return Subcode set to zero.

When the Proxy LSR is the egress of a MP2MP FEC, it can be either a
bud node or just an egress. LSP Pings sent from a leaf of a MP2MP
have different behavior in this case. MPLS Echo Requests are sent to
all upstream/downstream neighbors. The Proxy LSRs need to be
consistent with this variation in behavior. If the Proxy LSR is a
bud node or just an egress, an MPLS Proxy Ping Reply SHOULD be sent
to the Proxy Initiator with the return code set to 3, "Replying
router is an egress for the FEC at stack-depth", with Return Subcode
set to zero and DS/DDMAPs included only if the Proxy Initiator
requested information be returned in an MPLS Proxy Ping Reply. If
the Proxy LSR is not requested to return information in an MPLS Proxy
Ping Reply, the Proxy LSR SHOULD send MPLS Echo Request packets to
all upstream/downstream neighbors as would be done when sourcing an
LSP Ping from a MP2MP leaf (no MPLS Echo Reply is sent to the Proxy
Initiator indicating that the Proxy LSR is an egress).

3.2.2. Downstream Detailed Maps and Downstream Maps in Proxy Reply

When the Proxy LSR is a transit or bud node, downstream maps
corresponding to how the packet is transited cannot be supplied
unless an ingress interface for the MPLS Echo Request is specified.
Since this information is not available and all valid output paths
are of interest, the Proxy LSR SHOULD include DS/DDMAP(s) to describe
the entire set of paths that the packet can be replicated. This is
similar to the case in which an LSP Ping is initiated at the Proxy
LSR. For mLDP, there is a DS/DDMAP per upstream/downstream neighbor
for MP2MP LSPs, or per downstream neighbor in the P2MP LSP case.

When the Proxy LSR is a bud node or egress in an MP2MP LSP or a bud
node in a P2MP LSP, an LSP Ping initiated from the Proxy LSR would
source packets only to the neighbors but not itself, despite the fact
that the Proxy LSR is itself an egress for the FEC. In order to
match the behavior as seen from LSP Ping initiated at the Proxy LSR,
the Proxy Reply SHOULD contain DS/DDMAPs for only the paths to the
upstream/downstream neighbors, but no DS/DDMAP describing its own
egress paths. The proxy LSR identifies that it's an egress for the
FEC using a different Proxy Reply Return Code. The Proxy Reply
Return Code is either set to 19, "Replying router has FEC mapping for
topmost FEC", or 3, "Replying router is an egress for the FEC at
stack-depth".

3.2.3. Sending an MPLS Proxy Ping Reply

The Reply Mode, Sender's Handle, and Sequence Number fields are
copied from the Proxy Ping Request message. The TLVs specified above
are included. The message is encapsulated in a UDP packet. The
source IP address is a routable address of the Proxy LSR; the source
port is the well-known UDP port for LSP Ping. The destination IP
address and UDP port are copied from the source IP address and UDP
port of the MPLS Proxy Ping Request. The IP TTL is set to 255.

3.2.4. Sending the MPLS Echo Requests

An MPLS Echo Request is formed as described in the next section. The
section below describes how the MPLS Echo Request is sent on each
interface.

3.2.4.1. Forming the Base MPLS Echo Request

If Next Hop sub-TLVs were included in the received Proxy Echo
Parameters TLV, the Next_Hop_List is created from the addresses in
those sub-TLVs adjusted as described in Section 3.2. Otherwise, the
list is set to all the next hops to which the FEC would be forwarded.

The Proxy LSR then formats an MPLS Echo Request message. The Global
Flags and Reply Mode are copied from the Proxy Echo Parameters TLV.
The Return Code and Return Subcode are set to zero.

The Sender's Handle and Sequence Number are copied from the remote
MPLS Echo Request message.

The TimeStamp Sent is set to the time of day (in seconds and
microseconds) that the MPLS Echo Request is sent. The TimeStamp
Received is set to zero.

If the Reply-to Address TLV is present, it is used to set the MPLS
Echo Request source address; otherwise, the MPLS Echo Request source
address is set to the Proxy Request source address.

The following TLVs are copied from the MPLS Proxy Ping Request
message. Note that, of these, only the Target FEC Stack is REQUIRED
to appear in the MPLS Proxy Ping Request message. The Pad TLV is not
copied if the Proxy Echo Parameter TLV MPLS payload size is set to a
non-zero value.

Target FEC Stack

Pad

Vendor Enterprise Number

Reply TOS Byte

P2MP Responder Identifier [RFC6425]

Echo Jitter [RFC6425]

Vendor Private TLVs
If the Proxy Echo Parameter TLV MPLS payload size is non-zero, the
Proxy LSR introduces a Pad TLV such that size of the MPLS Echo
Request (including any IP and UDP header) is zero-padded to the
specified MPLS payload size. The first octet in the Value part of
the Pad TLV is set to 1, "Drop Pad TLV from reply", and the remaining
octets of the Value part of the Pad TLV are filled with zeros. If
the IP header is used to encapsulate the MPLS Echo Request, the DF
bit MUST be set to one.

The message is then encapsulated in a UDP packet. The source UDP
port is copied from the Proxy Echo Parameters TLV. The destination
port is copied from the MPLS Proxy Ping Request message.

The source IP address is set to a routable address specified in the
Reply-to Address TLV or the source address of the received Proxy
Request. Per usual, the TTL of the IP packet is set to 1.

If the Explicit Differentiated Services Code Point (DSCP) flag is
set, the Requested DSCP byte is examined. If the setting is
permitted, then the DSCP byte of the IP header of the MPLS Echo
Request message is set to that value. If the Proxy LSR does not
permit explicit control for the DSCP byte, the MPLS Proxy Echo
Parameters with the Explicit DSCP flag cleared MUST be included in
any MPLS Proxy Ping Reply message to indicate why an MPLS Echo
Request was not sent. The Return Code MUST be set to 17, "Proxy Ping
parameters need to be modified". If the Explicit DSCP flag is not
set, the Proxy LSR SHOULD set the MPLS Echo Request DSCP settings to
the value normally used to source LSP Ping packets.

3.2.4.2. Per-Interface Sending Procedures

The Proxy LSR now iterates through the Next_Hop_List modifying the
base MPLS Echo Request to form the MPLS Echo Request packet that is
then sent on that particular interface.

The outgoing label stack is determined for each next-hop address.
The TTL for the label corresponding to the FEC specified in the FEC
stack is set such that the TTL on the wire will be the TTL specified
in the Proxy Echo Parameters. If any additional labels are pushed
onto the stack, their TTLs are set to 255. This will ensure that the
requestor will not have control over tunnels not relevant to the FEC
being tested.

If the MPLS Proxy Ping Request message contained Downstream Mapping
TLVs or Downstream Detailed Mapping TLVs, they are examined. If the
Downstream IP address matches the next-hop address, that Downstream
Mapping TLV is included in the MPLS Echo Request.

The packet is then transmitted on this interface.

4. Proxy Ping Request/Reply Messages

This document defines two new LSP Ping messages, the MPLS Proxy Ping
Request and the MPLS Proxy Ping Reply.

4.1. Proxy Ping Request/Reply Message Formats

The packet format is as defined in [RFC4379]. Two new message types,
Proxy Ping Request and Reply, are being added.

Message Type

Type Message
---- -------
3 MPLS Proxy Ping Request
4 MPLS Proxy Ping Reply

4.2. Proxy Ping Request Message Contents

The MPLS Proxy Ping Request message MAY contain the following
TLVs:

Type TLV
---- -----------
1 Target FEC Stack
2 Downstream Mapping (DEPRECATED)
3 Pad
5 Vendor Enterprise Number
10 Reply TOS Byte
11 P2MP Responder Identifier [RFC6425]
12 Echo Jitter [RFC6425]
20 Downstream Detailed Mapping
21 Reply Path [RFC7110]
22 Reply TC [RFC7110]
23 Proxy Echo Parameters
24 Reply-to Address
* Vendor Private TLVs

* TLVs types in the Vendor Private TLV Space MUST be ignored if
not understood

4.3. Proxy Ping Reply Message Contents

The MPLS Proxy Ping Reply message MAY contain the following TLVs:

Type TLV
---- -----------
1 Target FEC Stack
2 Downstream Mapping (DEPRECATED)
5 Vendor Enterprise Number
9 Errored TLVs
20 Downstream Detailed Mapping
23 Proxy Echo Parameters
25 Upstream Neighbor Address
26 Downstream Neighbor Address (0 or more)
* Vendor Private TLVs

* TLVs types in the Vendor Private TLV Space MUST be ignored if
not understood

5. TLV Formats

5.1. Proxy Echo Parameters TLV

The Proxy Echo Parameters TLV is a TLV that MUST be included in an
MPLS Proxy Ping Request message. The length of the TLV is 12 + K +
S, where K is the length of the Destination IP Address field and S is
the total length of the sub-TLVs. The Proxy Echo Parameters TLV can
be used either to 1) control attributes used in composing and sending
an MPLS Echo Request or 2) query the Proxy LSR for information about
the topmost FEC in the target FEC stack, but not both. In the case
where the Proxy LSR is being queried (i.e., information needs to be
returned in an MPLS Proxy Ping Reply), no MPLS Echo Request will be
sent from the Proxy LSR. The MPLS Proxy Ping Request Proxy Echo
Parameters TLV's Proxy Flags SHOULD be set appropriately, as
described below.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | Reply Mode | Proxy Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | Rqst'd DSCP | Source UDP Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Flags | MPLS Payload Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Destination IP Address :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: :
: Sub-TLVs :
: :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Address Type

The type and length of the address found in the in the Destination
IP Address and Next Hop IP Addresses fields. The values are
shared with the Downstream Mapping Address Type Registry.

The type codes applicable in this case appear in the table below:

Address Family Type Length

IPv4 1 4
IPv6 3 16

Reply Mode

The reply mode to be sent in the MPLS Echo Request message; the
values are as specified in [RFC4379].

Proxy Flags

The Proxy Request Initiator sets zero, one, or more of these flags
to request actions at the Proxy LSR.

0x0001 Request for FEC Neighbor Address info

When set, this requests that the Proxy LSR supply the
Upstream and Downstream neighbor address information in the
MPLS Proxy Ping Reply message. This flag is only applicable
for the topmost FEC in the FEC stack if the FEC type
corresponds with a P2MP or MP2MP LSP. The Proxy LSR MUST
respond (as applicable) with Upstream Neighbor Address and
Downstream Neighbor Address TLV(s) in the MPLS Proxy Ping
Reply message. The Upstream Neighbor Address TLV needs be
included only if there is an upstream neighbor. Similarly,
one Downstream Neighbor Address TLV needs to be included for
each Downstream Neighbor from which the LSR learned
bindings.

Setting this flag will cause the Proxy LSR to cancel sending
any MPLS Echo Request. The initiator may use information
learned from the MPLS Proxy Ping Reply that is sent instead
to generate subsequent proxy requests.

0x0002 Request for Downstream Mapping

When set, this requests that the Proxy LSR supply a
Downstream Mapping TLV (see [RFC4379]) in the MPLS Proxy
Ping Reply message. Either this flag may be set or the
"Request for Downstream Detailed Mapping" flag may be set,
but not both.

Setting this flag will cause the Proxy LSR to cancel sending
an MPLS Echo Request. Information learned with such a Proxy
Reply may be used by the Proxy Initiator to generate
subsequent Proxy Requests.

0x0004 Request for Downstream Detailed Mapping

When set, this requests that the Proxy LSR supply a
Downstream Detailed Mapping TLV (see [RFC6424]) in the MPLS
Proxy Ping Reply message. It's not valid to have the
"Request for Downstream Mapping" flag set when this flag is
set. Setting this flag will cause the Proxy LSR to cancel
sending an MPLS Echo Request. The initiator may use
information learned from the MPLS Proxy Ping Reply that is
sent instead to generate subsequent proxy requests.

0x0008 Explicit DSCP Request

When set, this requests that the Proxy LSR use the supplied
"Rqst'd DSCP" byte in the Echo Request message
TTL

The TTL to be used in the label stack entry corresponding to
the topmost FEC in the MPLS Echo Request packet. Valid values
are in the range [1,255]. A setting of 0 SHOULD be ignored by
the Proxy LSR.

Requested DSCP

This field is valid only if the Explicit DSCP flag is set. If
not set, the field MUST be zero on transmission and ignored on
receipt. When the flag is set, this field contains the DSCP
value to be used in the MPLS Echo Request packet IP header.

Source UDP Port

The source UDP port to be sent in the MPLS Echo Request packet

Global Flags

The Global Flags to be sent in the MPLS Echo Request message

MPLS Payload Size

Used to request that the MPLS payload (IP header + UDP header +
MPLS Echo Request) be padded using a zero-filled Pad TLV so
that the IP header, UDP header, and MPLS Echo Request total the
specified size. Having the field set to zero means no size
request is being made. If the requested size is less than the
minimum size required to form the MPLS Echo Request, the
request will be treated as a best-effort request with the Proxy
LSR building the smallest possible packet (i.e., not using a
Pad TLV). The IP header DF bit MUST be set when this field is
non-zero.

Destination IP Address

If the Address Type is IPv4, an address from the range 127/8;
if the Address Type is IPv6, an address from the range
::ffff:7f00:0/104

Sub-TLVs

List of TLV-encoded sub-TLVs. Currently one is defined.

Sub-Type Length Sub-TLV Name
-------- ------ ------------
1 8+ Next Hop

5.1.1. Next Hop Sub-TLV

This sub-TLV is used to describe a particular next hop towards which
the Echo Request packet should be sent. If the topmost FEC in the
FEC stack is a multipoint LSP, this sub-TLV may appear multiple
times.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Type | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Hop IP Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Hop Interface (0, 4, or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Address Type

Type Type of Next Hop Addr Length Interface Field (IF)
Length
1 IPv4 Numbered 4 4
2 IPv4 Unnumbered 4 4
3 IPv6 Numbered 16 16
4 IPv6 Unnumbered 16 4
5 Reserved
6 IPv4 Protocol Adj 4 0
7 IPv6 Protocol Adj 16 0

Note: Types 1-4 correspond to the types in the DSMAP TLV.
They are expected to be populated with information
obtained through a previously returned DSMAP TLV. Types
6 and 7 are intended to be populated from the local
address information obtained from a previously returned
Downstream Neighbor Address TLV or Upstream Neighbor
Address TLV.

Next Hop IP Address

A next hop address that the Echo Request message is to be sent
towards

Next Hop Interface

Identifier of the interface through which the Echo Request
message is to be sent. For Addr Type 5 and 6, the Next Hop
interface field isn't used and MUST be of an associated byte
length of zero octets.

5.2. Reply-to Address TLV

Used to specify the MPLS Echo Request IP source address. This
address MUST be IP reachable via the Proxy LSR; otherwise, it will be
rejected.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Reply-to Address :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Address Type

A type code as specified in the table below:

Type Type of Address

1 IPv4
3 IPv6

5.3. Upstream Neighbor Address TLV

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Upst Addr Type |Local Addr Type| MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Upstream Address :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Local Address :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Upst Addr Type; Local Addr Type

These two fields determine the type and length of the
respective addresses. The codes are specified in the table
below:

Type Type of Address Length

0 No Address Supplied 0
1 IPv4 4
3 IPv6 16

Upstream Address

The address of the immediate upstream neighbor for the topmost
FEC in the FEC stack. If the protocol adjacency exists by
which the label for this FEC was exchanged, this address MUST
be the address used in that protocol exchange.

Local Address

The local address used in the protocol adjacency by which the
label for this FEC was exchanged.

5.4. Downstream Neighbor Address TLV

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Dnst Addr Type |Local Addr Type| MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Downstream Address :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Local Address :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Dnst Addr Type; Local Addr Type

These two fields determine the type and length of the
respective addresses. The codes are specified in the table
below:

Type Type of Address Length

0 No Address Supplied 0
1 IPv4 4
3 IPv6 16
Downstream Address

The address of an immediate downstream neighbor for the topmost
FEC in the FEC stack. If the protocol adjacency exists by
which the label for this FEC was exchanged, this address MUST
be the address used in that protocol exchange.

Local Address

The local address used in the protocol adjacency by which the
label for this FEC was exchanged.

6. Security Considerations

The mechanisms described in this document are intended to be used
within a service provider network and to be initiated only under the
authority of that administration.

If such a network also carries Internet traffic, or permits IP access
from other administrations, the MPLS Proxy Ping message SHOULD be
discarded at the points where IP packets are received from other
administrations. This can be accomplished by filtering on source
address or by filtering all MPLS ping messages on UDP port.

Any node that acts as a Proxy LSR SHOULD validate requests against a
set of valid source addresses. An implementation MUST provide such
filtering capabilities.

MPLS Proxy Ping Request messages are IP addressed directly to the
Proxy LSR. If a Proxy LSR receives an MPLS Proxy Ping message via
expiration of the IP or Label Stack Entry TTL, it MUST NOT be acted
upon.

If an MPLS Proxy Ping Request IP source address is not IP reachable
by the Proxy LSR, the Proxy Request MUST NOT be acted upon.

MPLS Proxy Ping Requests are limited to making their request via the
specification of a FEC. This ensures that only valid MPLS Echo
Request messages can be created. No label-spoofing attacks are
possible.

7. IANA Considerations

Per this document, IANA has made the following assignments.

MPLS LSP Ping Message Types

Value Meaning
----- -------
3 MPLS Proxy Ping Request
4 MPLS Proxy Ping Reply

TLVs

Type TLV Name
---- --------
23 Proxy Echo Parameters
24 Reply-to Address
25 Upstream Neighbor Address
26 Downstream Neighbor Address

Return Codes

Value Meaning
----- -------
16 Proxy Ping not authorized
17 Proxy Ping parameters need to be modified
18 MPLS Echo Request could not be sent
19 Replying router has FEC mapping for topmost FEC

7.1. Proxy Echo Parameters Sub-TLVs

The IANA has created and maintains this new registry for Proxy Echo
Parameters Sub-TLVs. Assignments will use the same rules spelled out
in Section 7.2 of [RFC4379].

Sub-Type Sub-TLV Name
-------- ------------
0 Reserved
1 Next Hop

7.2. Proxy Flags

IANA has created and maintains a new registry for the Proxy Flags
that are used with the Proxy Echo Parameters TLV. See Section 5.1
for details. The registry is in the "Multi-Protocol Label Switching
(MPLS) Label Switched Paths (LSPs) Ping Parameters" registry in the
"Multiprotocol Label Switching Architecture (MPLS)" name space. The
registration procedure is Standards Action [RFC5226]. The initial
values are as follows.

Bit Number Name
---------- ----
0 Request for FEC Neighbor Address info
1 Request for Downstream Mapping
2 Request for Downstream Detailed Mapping
3 Explicit DSCP Request
4-15 Unassigned

7.3. Downstream Address Mapping Registry

This document makes the following assignments in the Downstream
Address Mapping Registry. This document updates the registry defined
by [RFC6426]. The registration procedure remains Standards Action
and a note has been added as follows:

When a code point is assigned that is not also assigned in the
Next Hop Address Type Registry, the code point there must be
marked "Reserved".

Type # Address Type K Octets
------ ------------ --------
6 Reserved N/A RFC 7555
7 Reserved N/A RFC 7555

7.4. Next Hop Sub-TLV Address Type Registry

IANA has created a new registry called the "Next Hop Address Type
Registry". The allocation policy for this registry is Standards
Action. Further, a note has been added as follows:

When a code point is assigned that is not also assigned in the
Downstream Address Mapping Registry, the code point there must be
marked "Reserved".

The initial allocations are:

Type Type of Next Hop Addr Length IF Length Reference

1 IPv4 Numbered 4 4 [RFC4379]
2 IPv4 Unnumbered 4 4 [RFC4379]
3 IPv6 Numbered 16 16 [RFC4379]
4 IPv6 Unnumbered 16 4 [RFC4379]
5 Reserved RFC 7555
6 IPv4 Protocol Adj 4 0 RFC 7555
7 IPv6 Protocol Adj 16 0 RFC 7555
8-255 Unassigned

8. References

8.1. 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>.

[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
DOI 10.17487/RFC4379, February 2006,
<http://www.rfc-editor.org/info/rfc4379>.

[RFC6424] Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
Performing Label Switched Path Ping (LSP Ping) over MPLS
Tunnels", RFC 6424, DOI 10.17487/RFC6424, November 2011,
<http://www.rfc-editor.org/info/rfc6424>.

[RFC6425] Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
Failures in Point-to-Multipoint MPLS - Extensions to LSP
Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
<http://www.rfc-editor.org/info/rfc6425>.

[RFC6426] Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
On-Demand Connectivity Verification and Route Tracing",
RFC 6426, DOI 10.17487/RFC6426, November 2011,
<http://www.rfc-editor.org/info/rfc6426>.

[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014,
<http://www.rfc-editor.org/info/rfc7110>.

8.2. Informative References

[RFC4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
Yasukawa, Ed., "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
DOI 10.17487/RFC4875, May 2007,
<http://www.rfc-editor.org/info/rfc4875>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.

[RFC6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
Thomas, "Label Distribution Protocol Extensions for Point-
to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
<http://www.rfc-editor.org/info/rfc6388>.

Acknowledgements

The authors would like to thank Nobo Akiya, Adrian Farrel, Tom Yu,
Tom Taylor, and Warren Kumari for their detailed reviews and
insightful comments.

Authors' Addresses

George Swallow
Cisco Systems
1414 Massachusetts Ave
Boxborough, MA 01719
United States

EMail: swallow@cisco.com

Vanson Lim
Cisco Systems
1414 Massachusetts Avenue
Boxborough, MA 01719
United States

EMail: vlim@cisco.com

Sam Aldrin
Huawei Technologies
2330 Central Express Way
Santa Clara, CA 95951
United States

EMail: aldrin.ietf@gmail.com