Network Working Group S. Saxena, Ed.
Internet-Draft Cisco Systems, Inc.
Intended Status: Standards Track A. Farrel
Updates: 4379 (if approved) Old Dog Consulting
Expires: April 17, 2011 S. Yasukawa
NTT Corporation
October 18, 2010
Detecting Data Plane Failures in Point-to-Multipoint Multiprotocol
Label Switching (MPLS) - Extensions to LSP Ping
draft-ietf-mpls-p2mp-lsp-ping-12.txt
Status of this Memo
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Abstract
Recent proposals have extended the scope of Multiprotocol Label
Switching (MPLS) Label Switched Paths (LSPs) to encompass
point-to-multipoint (P2MP) LSPs.
The requirement for a simple and efficient mechanism that can be used
to detect data plane failures in point-to-point (P2P) MPLS LSPs has
been recognized and has led to the development of techniques for
fault detection and isolation commonly referred to as "LSP Ping".
The scope of this document is fault detection and isolation for P2MP
MPLS LSPs. This documents does not replace any of the mechanisms of
LSP Ping, but clarifies their applicability to MPLS P2MP LSPs, and
extends the techniques and mechanisms of LSP Ping to the MPLS P2MP
environment.
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
Conventions used in this document
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 RFC 2119 [RFC2119].
Contents
1. Introduction.................................................... 3
1.1. Design Considerations......................................... 4
2. Notes on Motivation............................................. 4
2.1. Basic Motivations for LSP Ping................................ 4
2.2. Motivations for LSP Ping for P2MP LSPs........................ 5
3. Packet Format................................................... 7
3.1. Identifying the LSP Under Test................................ 7
3.1.1. Identifying a P2MP MPLS TE LSP.............................. 7
3.1.1.1. RSVP P2MP IPv4 Session Sub-TLV............................ 8
3.1.1.2. RSVP P2MP IPv6 Session Sub-TLV............................ 8
3.1.2. Identifying a Multicast LDP LSP............................. 9
3.1.2.1. Multicast LDP FEC Stack Sub-TLVs.......................... 9
3.1.2.2. Applicability to Multipoint-to-Multipoint LSPs........... 11
3.2. Limiting the Scope of Responses.............................. 11
3.2.1. Egress Address P2MP Responder Identifier Sub-TLVs.......... 12
3.2.2. Node Address P2MP Responder Identifier Sub-TLVs............ 12
3.3. Preventing Congestion of Echo Responses...................... 12
3.4. Respond Only If TTL Expired Flag............................. 13
3.5. Downstream Detailed Mapping TLV.............................. 14
4. Operation of LSP Ping for a P2MP LSP........................... 14
4.1. Initiating Router Operations................................. 14
4.1.1. Limiting Responses to Echo Requests........................ 15
4.1.2. Jittered Responses to Echo Requests........................ 15
4.2. Responding Router Operations................................. 16
4.2.1. Echo Response Reporting.................................... 17
4.2.1.1. Responses from Transit and Branch nodes.................. 17
4.2.1.2. Responses from Egress Nodes.............................. 18
4.2.1.3. Responses from Bud Nodes................................. 18
4.3. Special Considerations for Traceroute........................ 20
4.3.1. End of Processing for Traceroutes.......................... 20
4.3.2. Multiple responses from Bud and Egress Nodes............... 21
4.3.3. Non-Response to Traceroute Echo Requests................... 21
4.3.4. Use of Downstream Detailed Mapping TLV in Echo Request..... 21
4.3.5 Cross Over Node Processing.................................. 22
5. Non-compliant Routers.......................................... 22
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6. OAM Considerations............................................. 23
7. IANA Considerations............................................ 23
7.1. New Sub-TLV Types............................................ 23
7.2. New TLVs..................................................... 24
8. Security Considerations........................................ 24
9. Acknowledgements............................................... 24
10. References.................................................... 24
10.1. Normative References........................................ 25
10.2. Informative References...................................... 25
11. Authors' Addresses............................................ 26
12. Full Copyright Statement...................................... 26
1. Introduction
Simple and efficient mechanisms that can be used to detect data plane
failures in point-to-point (P2P) Multiprotocol Label Switching (MPLS)
Label Switched Paths (LSP) are described in [RFC4379]. The
techniques involve information carried in MPLS "Echo Request" and
"Echo Reply" messages, and mechanisms for transporting them. The
echo request and reply messages provide sufficient information to
check correct operation of the data plane, as well as a mechanism to
verify the data plane against the control plane, and thereby localize
faults. The use of reliable channels for echo reply messages as
described in [RFC4379] enables more robust fault isolation. This
collection of mechanisms is commonly referred to as "LSP Ping".
The requirements for point-to-multipoint (P2MP) MPLS traffic
engineered (TE) LSPs are stated in [RFC4461]. [RFC4875] specifies a
signaling solution for establishing P2MP MPLS TE LSPs.
The requirements for point-to-multipoint extensions to the Label
Distribution Protocol (LDP) are stated in [P2MP-LDP-REQ]. [P2MP-LDP]
specifies extensions to LDP for P2MP MPLS.
P2MP MPLS LSPs are at least as vulnerable to data plane faults or to
discrepancies between the control and data planes as their P2P
counterparts. Therefore, mechanisms are needed to detect such data
plane faults in P2MP MPLS LSPs as described in [RFC4687].
This document extends the techniques described in [RFC4379] such that
they may be applied to P2MP MPLS LSPs. This document stresses the
reuse of existing LSP Ping mechanisms used for P2P LSPs, and applies
them to P2MP MPLS LSPs in order to simplify implementation and
network operation.
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1.1. Design Considerations
An important consideration for designing LSP Ping for P2MP MPLS LSPs
is that every attempt is made to use or extend existing mechanisms
rather than invent new mechanisms.
As for P2P LSPs, a critical requirement is that the echo request
messages follow the same data path that normal MPLS packets traverse.
However, it can be seen this notion needs to be extended for P2MP
MPLS LSPs, as in this case an MPLS packet is replicated so that it
arrives at each egress (or leaf) of the P2MP tree.
MPLS echo requests are meant primarily to validate the data plane,
and they can then be used to validate data plane state against the
control plane. They may also be used to bootstrap other OAM
procedures such as [RFC5884]. As pointed out in [RFC4379],
mechanisms to check the liveness, function, and consistency of the
control plane are valuable, but such mechanisms are not a feature of
LSP Ping and are not covered in this document.
As is described in [RFC4379], to avoid potential Denial of Service
attacks, it is RECOMMENDED to regulate the LSP Ping traffic passed to
the control plane. A rate limiter should be applied to the
well-known UDP port defined for use by LSP Ping traffic.
2. Notes on Motivation
2.1. Basic Motivations for LSP Ping
The motivations listed in [RFC4379] are reproduced here for
completeness.
When an LSP fails to deliver user traffic, the failure cannot always
be detected by the MPLS control plane. There is a need to provide a
tool that enables users to detect such traffic "black holes" or
misrouting within a reasonable period of time. A mechanism to
isolate faults is also required.
[RFC4379] describes a mechanism that accomplishes these goals. This
mechanism is modeled after the ping/traceroute paradigm: ping (ICMP
echo request [RFC792]) is used for connectivity checks, and
traceroute is used for hop-by-hop fault localization as well as path
tracing. [RFC4379] specifies a "ping mode" and a "traceroute" mode
for testing MPLS LSPs.
The basic idea as expressed in [RFC4379] is to test that the packets
that belong to a particular Forwarding Equivalence Class (FEC)
actually end their MPLS path on an LSR that is an egress for that
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FEC. [RFC4379] achieves this test by sending a packet (called an
"MPLS echo request") along the same data path as other packets
belonging to this FEC. An MPLS echo request also carries information
about the FEC whose MPLS path is being verified. This echo request
is forwarded just like any other packet belonging to that FEC. In
"ping" mode (basic connectivity check), the packet should reach the
end of the path, at which point it is sent to the control plane of
the egress LSR, which then verifies that it is indeed an egress for
the FEC. In "traceroute" mode (fault isolation), the packet is sent
to the control plane of each transit LSR, which performs various
checks that it is indeed a transit LSR for this path; this LSR also
returns further information that helps to check the control plane
against the data plane, i.e., that forwarding matches what the
routing protocols determined as the path.
One way these tools can be used is to periodically ping a FEC to
ensure connectivity. If the ping fails, one can then initiate a
traceroute to determine where the fault lies. One can also
periodically traceroute FECs to verify that forwarding matches the
control plane; however, this places a greater burden on transit LSRs
and should be used with caution.
2.2. Motivations for LSP Ping for P2MP LSPs
As stated in [RFC4687], MPLS has been extended to encompass P2MP
LSPs. As with P2P MPLS LSPs, the requirement to detect, handle, and
diagnose control and data plane defects is critical. For operators
deploying services based on P2MP MPLS LSPs, the detection and
specification of how to handle those defects is important because
such defects may affect the fundamentals of an MPLS network, but also
because they may impact service level specification commitments for
customers of their network.
P2MP LDP [P2MP-LDP] uses the Label Distribution Protocol to establish
multicast LSPs. These LSPs distribute data from a single source to
one or more destinations across the network according to the next
hops indicated by the routing protocols. Each LSP is identified by
an MPLS multicast FEC.
P2MP MPLS TE LSPs [RFC4875] may be viewed as MPLS tunnels with a
single ingress and multiple egresses. The tunnels, built on P2MP
LSPs, are explicitly routed through the network. There is no concept
or applicability of a FEC in the context of a P2MP MPLS TE LSP.
MPLS packets inserted at the ingress of a P2MP LSP are delivered
equally (barring faults) to all egresses. In consequence, the basic
idea of LSP Ping for P2MP MPLS TE LSPs may be expressed as an
intention to test that packets that enter (at the ingress) a
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particular P2MP LSP actually end their MPLS path on the LSRs that are
the (intended) egresses for that LSP. The idea may be extended to
check selectively that such packets reach specific egresses.
The technique in this document makes this test by sending an LSP Ping
echo request message along the same data path as the MPLS packets.
An echo request also carries the identification of the P2MP MPLS LSP
(multicast LSP or P2MP TE LSP) that it is testing. The echo request
is forwarded just as any other packet using that LSP, and so is
replicated at branch points of the LSP and should be delivered to all
egresses.
In "ping" mode (basic connectivity check), the echo request should
reach the end of the path, at which point it is sent to the control
plane of the egress LSRs, which verify that they are indeed an egress
(leaf) of the P2MP LSP. An echo response message is sent by an
egress to the ingress to confirm the successful receipt (or announce
the erroneous arrival) of the echo request.
In "traceroute" mode (fault isolation), the echo request is sent to
the control plane at each transit LSR, and the control plane checks
that it is indeed a transit LSR for this P2MP MPLS LSP. The transit
LSR returns information about the outgoing paths. This
information can be used by ingress LSR to build topology or by
downstream LSRs to do extra label verification.
P2MP MPLS LSPs may have many egresses, and it is not necessarily the
intention of the initiator of the ping or traceroute operation to
collect information about the connectivity or path to all egresses.
Indeed, in the event of pinging all egresses of a large P2MP MPLS
LSP, it might be expected that a large number of echo responses would
arrive at the ingress independently but at approximately the same
time. Under some circumstances this might cause congestion at or
around the ingress LSR. The procedures described in this document
provide two mechanisms to control echo responses.
The first procedure allows the responders to randomly delay (or
jitter) their responses so that the chances of swamping the ingress
are reduced. The second procedures allows the initiator to limit the
scope of an LSP Ping echo request (ping or traceroute mode) to one
specific intended egress.
LSP Ping can be used to periodically ping a P2MP MPLS LSP to ensure
connectivity to any or all of the egresses. If the ping fails, the
operator or an automated process can then initiate a traceroute to
determine where the fault is located within the network. A
traceroute may also be used periodically to verify that data plane
forwarding matches the control plane state; however, this places an
increased burden on transit LSRs and should be used infrequently and
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with caution.
3. Packet Format
The basic structure of the LSP Ping packet remains the same as
described in [RFC4379]. Some new TLVs and sub-TLVs are required to
support the new functionality. They are described in the following
sections.
3.1. Identifying the LSP Under Test
3.1.1. Identifying a P2MP MPLS TE LSP
[RFC4379] defines how an MPLS TE LSP under test may be identified in
an echo request. A Target FEC Stack TLV is used to carry either an
RSVP IPv4 Session or an RSVP IPv6 Session sub-TLV.
In order to identify the P2MP MPLS TE LSP under test, the echo
request message MUST carry a Target FEC Stack TLV, and this MUST
carry exactly one of two new sub-TLVs: either an RSVP P2MP IPv4
Session sub-TLV or an RSVP P2MP IPv6 Session sub-TLV. These sub-TLVs
carry fields from the RSVP-TE P2MP Session and Sender-Template
objects [RFC4875] and so provide sufficient information to uniquely
identify the LSP.
The new sub-TLVs are assigned sub-type identifiers as follows, and
are described in the following sections.
Sub-Type # Length Value Field
---------- ------ -----------
TBD 20 RSVP P2MP IPv4 Session
TBD 56 RSVP P2MP IPv6 Session
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3.1.1.1. RSVP P2MP IPv4 Session Sub-TLV
The format of the RSVP P2MP IPv4 Session sub-TLV value field is
specified in the following figure. The value fields are taken from
the definitions of the P2MP IPv4 LSP Session Object and the P2MP IPv4
Sender-Template Object in [RFC4875]. Note that the Sub-Group ID of
the Sender-Template is not required.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P2MP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel sender address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.1.1.2. RSVP P2MP IPv6 Session Sub-TLV
The format of the RSVP P2MP IPv6 Session sub-TLV value field is
specified in the following figure. The value fields are taken from
the definitions of the P2MP IPv6 LSP Session Object, and the P2MP
IPv6 Sender-Template Object in [RFC4875]. Note that the Sub-Group ID
of the Sender-Template is not required.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| P2MP ID |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Extended Tunnel ID |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 tunnel sender address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.1.2. Identifying a Multicast LDP LSP
[RFC4379] defines how a P2P LDP LSP under test may be identified in
an echo request. A Target FEC Stack TLV is used to carry one or more
sub-TLVs (for example, an IPv4 Prefix FEC sub-TLV) that identify the
LSP.
In order to identify a multicast LDP LSP under test, the echo request
message MUST carry a Target FEC Stack TLV, and this MUST carry
exactly one of two new sub-TLVs: either a Multicast P2MP LDP FEC
Stack sub-TLV or a Multicast MP2MP LDP FEC Stack sub-TLV. These
sub-TLVs use fields from the multicast LDP messages [P2MP-LDP] and so
provides sufficient information to uniquely identify the LSP.
The new sub-TLVs are assigned a sub-type identifiers as follows, and
are described in the following section.
Sub-Type # Length Value Field
---------- ------ -----------
TBD Variable Multicast P2MP LDP FEC Stack
TBD Variable Multicast MP2MP LDP FEC Stack
3.1.2.1. Multicast LDP FEC Stack Sub-TLVs
Both Multicast P2MP and MP2MP LDP FEC Stack have the same format, as
specified in the following figure.
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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 Family | Address Length| Root LSR Addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Root LSR Address (Cont.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family
Two octet quantity containing a value from ADDRESS FAMILY NUMBERS
in [IANA-PORT] that encodes the address family for the Root LSR
Address.
Address Length
Length of the Root LSR Address in octets.
Root LSR Address
Address of the LSR at the root of the P2MP LSP encoded according
to the Address Family field.
Opaque Length
The length of the Opaque Value, in octets. Depending on length of
the Root LSR Address, this field may not be aligned to a word
boundary.
Opaque Value
An opaque value element which uniquely identifies the P2MP LSP in
the context of the Root LSR.
If the Address Family is IPv4, the Address Length MUST be 4. If the
Address Family is IPv6, the Address Length MUST be 16. No other
Address Family values are defined at present.
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3.1.2.2. Applicability to Multipoint-to-Multipoint LSPs
The mechanisms defined in this document can be extended to include
Multipoint-to-Multipoint (MP2MP) Multicast LSPs. In an MP2MP LSP
tree, any leaf node can be treated like a head node of a P2MP tree.
In other words, for MPLS OAM purposes, the MP2MP tree can be treated
like a collection of P2MP trees, with each MP2MP leaf node acting
like a P2MP head-end node. When a leaf node is acting like a P2MP
head-end node, the remaining leaf nodes act like egress or bud nodes.
3.2. Limiting the Scope of Responses
A new TLV is defined for inclusion in the Echo request message.
The P2MP Responder Identifier TLV is assigned the TLV type value TBD
and is encoded as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=TBD(P2MP Responder ID TLV)| Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Sub-TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-TLVs:
Zero, one or more sub-TLVs as defined below.
If no sub-TLVs are present, the TLV MUST be processed as if it
were absent. If more than one sub-TLV is present the first MUST
be processed as described in this document, and subsequent
sub-TLVs SHOULD be ignored.
The P2MP Responder Identifier TLV only has meaning on an echo request
message. If present on an echo response message, it SHOULD be
ignored.
Four sub-TLVs are defined for inclusion in the P2MP Responder
Identifier TLV carried on the echo request message. These are:
Sub-Type # Length Value Field
---------- ------ -----------
1 4 IPv4 Egress Address P2MP Responder Identifier
2 16 IPv6 Egress Address P2MP Responder Identifier
3 4 IPv4 Node Address P2MP Responder Identifier
4 16 IPv6 Node Address P2MP Responder Identifier
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The content of these Sub-TLVs are defined in the following sections.
Also defined is the intended behavior of the responding node upon
receiving any of these Sub-TLVs.
3.2.1. Egress Address P2MP Responder Identifier Sub-TLVs
The IPv4 or IPv6 Egress Address P2MP Responder Identifier Sub-TLVs
MAY be used in an echo request carrying RSVP P2MP Session Sub-TLV.
They SHOULD NOT be used with an echo request carrying Multicast LDP
FEC Stack Sub-TLV. If a node receives these TLVs in an echo request
carrying Multicast LDP then it SHOULD ignore these sub-TLVs and
respond as if they are not present. Hence these TLVs cannot be used
to traceroute to a single node when Multicast LDP FEC is used.
A node that receives an echo request with this Sub-TLV present MUST
respond only if the node lies on the path to the address in the
Sub-TLV.
The address in this Sub-TLV SHOULD be of an egress or bud node and
SHOULD NOT be of a transit or branch node. A transit or branch node,
should be able to determine if the address in this Sub-TLV is for an
egress or bud node which is reachable through it. Hence, this
address SHOULD be known to the nodes upstream of the target node, for
instance via control plane signaling. As a case in point, if RSVP-TE
is used to signal the P2MP LSP, this address SHOULD be the address
used in destination address field of the S2L_SUB_LSP object, when
corresponding egress or bud node is signaled.
3.2.2. Node Address P2MP Responder Identifier Sub-TLVs
The IPv4 or IPv6 Node Address P2MP Responder Identifier Sub-TLVs MAY
be used in an echo request carrying either RSVP P2MP Session or
Multicast LDP FEC Stack Sub-TLV.
A node that receives an echo request with this Sub-TLV present MUST
respond only if the address in the Sub-TLV corresponds to any address
that is local to the node. This address in the Sub-TLV may be of any
physical interface or may be the router id of the node itself.
The address in this Sub-TLV SHOULD be of any transit, branch, bud or
egress node for that P2MP LSP.
3.3. Preventing Congestion of Echo Responses
A new TLV is defined for inclusion in the Echo request message.
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The Echo Jitter TLV is assigned the TLV type value TBD and is encoded
as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TBD (Jitter TLV) | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Jitter time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Jitter time:
This field specifies the upper bound of the jitter period that
should be applied by a responding node to determine how long to
wait before sending an echo response. A responding node SHOULD
wait a random amount of time between zero milliseconds and the
value specified in this field.
Jitter time is specified in milliseconds.
The Echo Jitter TLV only has meaning on an echo request message. If
present on an echo response message, it SHOULD be ignored.
3.4. Respond Only If TTL Expired Flag
A new flag is being introduced in the Global Flags field. The new
format of the Global Flags field is:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |T|V|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The V flag is described in [RFC4379].
The T (Respond Only If TTL Expired) flag SHOULD be set only in the
echo request packet by the sender. This flag SHOULD NOT be set in
the echo reply packet. If this flag is set in an echo reply packet,
then it MUST be ignored.
If the T flag is set to 1, then the reciever SHOULD reply only if the
TTL of the incoming MPLS label is equal to 1; if the TTL is more than
1, then no response should be sent back. If there is no incoming
MPLS label on the echo request packet, then this bit SHOULD be
ignored.
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If the T flag is set to 0, then the receiver SHOULD reply as per
regular processing.
3.5. Downstream Detailed Mapping TLV
Downstream Detailed Mapping TLV is described in [DDMT]. A transit,
branch or bud node can use the Downstream Detailed Mapping TLV to
return multiple Return Codes for different downstream paths. This
functionality can not be achieved via the Downstream Mapping TLV. As
per Section 4.3 of [DDMT], the Downstream Mapping TLV as described in
[RFC4379] is being deprecated.
Therefore for P2MP, a node MUST support Downstream Detailed Mapping
TLV. The Downstream Mapping TLV [RFC4379] is not appropriate for P2MP
traceroute functionality and SHOULD NOT be included in an Echo Request
message. When responding to an RSVP IPv4/IPv6 P2MP Session FEC Type
or a Multicast P2MP/MP2MP LDP FEC Type, a node MUST ignore any
Downstream Mapping TLV it receives in the echo request and MUST
continue processing as if the Downstream Mapping TLV is not present.
The details of the Return Codes to be used in the Downstream Detailed
Mapping TLV are provided in section 4.
4. Operation of LSP Ping for a P2MP LSP
This section describes how LSP Ping is applied to P2MP MPLS LSPs. As
mentioned previously, an important design consideration has been to
extend existing LSP Ping mechanism in [RFC4379] rather than invent
new mechanisms.
As specified in [RFC4379], MPLS LSPs can be tested via a "ping" mode
or a "traceroute" mode. The ping mode is also known as "connectivity
verification" and traceroute mode is also known as "fault isolation".
Further details can be obtained from [RFC4379].
This section specifies processing of echo requests for both ping and
traceroute mode at various nodes (ingress, transit, etc.) of the P2MP
LSP.
4.1. Initiating Router Operations
The router initiating the echo request will follow the procedures in
[RFC4379]. The echo request will contain a Target FEC Stack TLV. To
identify the P2MP LSP under test, this TLV will contain one of the
new sub-TLVs defined in section 3.1. Additionally there may be other
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optional TLVs present.
4.1.1. Limiting Responses to Echo Requests
As described in Section 2.2, it may be desirable to restrict the
operation of P2MP ping or traceroute to a single egress. Since echo
requests are forwarded through the data plane without interception by
the control plane, there is no facility to limit the propagation of
echo requests, and they will automatically be forwarded to all
reachable egresses.
However, a single egress may be identified by the inclusion of a P2MP
Responder Identifier TLV. The details of this TLV and its Sub-TLVs
are in section 3.2. There are two main types of sub-TLV in the P2MP
Responder Identifier TLV: Egress Address sub-TLV and Node Address
sub-TLV.
These sub-TLVs limit the responses either to the specified router
only or to any router on the path to the specified router. The
former capability is generally useful for ping mode, while the latter
is more suited to traceroute mode. An initiating router may indicate
that it wishes all egresses to respond to an echo request by omitting
the P2MP Responder Identifier TLV.
4.1.2. Jittered Responses to Echo Requests
The initiating router MAY request the responding routers to introduce
a random delay (or jitter) before sending the response. The
randomness of the delay allows the responses from multiple egresses
to be spread over a time period. Thus this technique is particularly
relevant when the entire P2MP LSP is being pinged or traced since it
helps prevent the initiating (or nearby) routers from being swamped
by responses, or from discarding responses due to rate limits that
have been applied.
It is desirable for the initiating rotuer to be able to control the
bounds of the jitter. If the tree size is small, only a small amount
of jitter is required, but if the tree is large, greater jitter is
needed.
The initiating router can supply the desired value of the jitter in
the Echo Jitter TLV as defined section 3.3. If this TLV is present,
the responding router MUST delay sending a response for a random
amount of time between zero milliseconds and the value indicated in
the TLV. If the TLV is absent, the responding egress SHOULD NOT
introduce any additional delay in responding to the echo request.
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LSP ping SHOULD NOT be used to attempt to measure the round-trip time
for data delivery. This is because the P2MP LSPs are unidirectional,
and the echo response is often sent back through the control plane.
The timestamp fields in the echo request and echo response packets
MAY be used to deduce some information about delivery times and
particularly the variance in delivery times.
The use of echo jittering does not change the processes for gaining
information, but note that the responding node MUST set the value in
the Timestamp Received fields before applying any delay.
Echo response jittering SHOULD be used for P2MP LSPs. If the Echo
Jitter TLV is present in an echo request for any other type of LSPs,
the responding egress MAY apply the jitter behavior as described
here.
4.2. Responding Router Operations
Usually the echo request packet will reach the egress and bud nodes.
In case of TTL Expiry, i.e. traceroute mode, the echo request packet
may stop at branch or transit nodes. In both scenarios, the echo
request will be passed on to control plane for reply processing.
The operations at the receiving node are an extenstion to the
existing processing as specified in [RFC4379]. A responding router
is RECOMMENDED to rate limit its receipt of echo request messages.
After rate limiting, the responding router must verify general sanity
of the packet. If the packet is malformed, or certain TLVs are not
understood, the [RFC4379] procedures must be followed for echo reply.
Similarly the Reply Mode field determines if the response is required
or not (and the mechanism to send it back).
For P2MP LSP ping and traceroute, i.e. if the echo request is
carrying an RSVP P2MP FEC or a Multicast LDP FEC, the responding
router MUST determine whether it is part of the P2MP LSP in question
by checking with the control plane.
- If the node is not part of the P2MP LSP, it MUST respond
according to [RFC4379] processing rules.
- If the node is part of the P2MP LSP, the node must check whether
the echo request is directed to it or not.
- If a P2MP Responder Identifier TLV is present, then the node
must follow the procedures defined in section 3.2 to
determine whether it should respond to the reqeust or not.
The presence of a P2MP Responder Identifier TLV or a
Downstream Detailed Mapping TLV might affect the Return Code.
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This is discussed in more detail later.
- If the P2MP Responder Identifier TLV is not present (or, in
the error case, is present, but does not contain any
sub-TLVs), then the node MUST respond according to [RFC4379]
processing rules.
4.2.1. Echo Response Reporting
Echo response messages carry return codes and subcodes to indicate
the result of the LSP Ping (when the ping mode is being used) as
described in [RFC4379].
When the responding node reports that it is an egress, it is clear
that the echo response applies only to the reporting node.
Similarly, when a node reports that it does not form part of the LSP
described by the FEC (i.e. there is a misconnection) then the echo
response applies to the reporting node.
However, it should be noted that an echo response message that
reports an error from a transit node may apply to multiple egress
nodes (i.e. leaves) downstream of the reporting node. In the case of
the ping mode of operation, it is not possible to correlate the
reporting node to the affected egresses unless the topology of the
P2MP tree is already known, and it may be necessary to use the
traceroute mode of operation to further diagnose the LSP.
Note also that a transit node may discover an error but also
determine that while it does lie on the path of the LSP under test,
it does not lie on the path to the specific egress being tested. In
this case, the node SHOULD NOT generate an echo response.
The following sections describe the expected values of Return Codes
for various nodes in a P2MP LSP. It is assumed that the sanity and
other checks have been performed and an echo response is being sent
back. As mentioned previously, the Return Code might change based on
the presence of Responder Identifier TLV or Downstream Detailed
Mapping TLV.
4.2.1.1. Responses from Transit and Branch nodes
The presence of a Responder Identifier TLV does not influence the
choice of the Return Code, which MAY be set to value 8 ('Label
switched at stack-depth <RSC>') or any other error value as needed.
The presence of a Downstream Detailed Mapping TLV will influence the
choice of Return Code. As per [DDMT], the Return Code in the echo
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response header MAY be set to value TBD ('See DDM TLV for Return Code
and Return SubCode') as defined in [DDMT]. The Return Code for each
Downstream Detailed Mapping TLV will depend on the downstream path as
described in [DDMT].
There will be a Downstream Detailed Mapping TLV for each downstream
path being reported in the echo response. Hence for transit nodes,
there will be only one such TLV and for branch nodes, there will be
more than one. If there is an Egress Address Responder Identifier
Sub-TLV, then the branch node will include only one Downstream
Detailed Mapping TLV corresponding to the downstream path required to
reach the address specified in the Egress Address Sub-TLV.
4.2.1.2. Responses from Egress Nodes
The presence of a Responder Identifier TLV does not influence the
choice of the Return Code, which MAY be set to value 3 ('Replying
router is an egress for the FEC at stack-depth <RSC>') or any other
error value as needed.
The presence of the Downstream Detailed Mapping TLV does not
influence the choice of Return Code. Egress nodes do not put in any
Downstream Detailed Mapping TLV in the echo response.
4.2.1.3. Responses from Bud Nodes
The case of bud nodes is more complex than other types of nodes. The
node might behave as either an egress node or a transit node or a
combination of an egress and branch node. This behavior is
determined by the presence of any Responder Identifier TLV and the
type of sub-TLV in it. Similarly Downstream Detailed Mapping TLV can
influence the Return Code values.
To determine the behavior of the bud node, use the following
guidelines. The intent of these guidelines is to figure out if the
echo request is meant for all nodes, or just this node, or for
another node reachable through this node or for a different section
of the tree. In the first case, the node will behave like a
combination of egress and branch node; in the second case, the node
will behave like pure egress node; in the third case, the node will
behave like a transit node; and in the last case, no response will be
sent back.
Node behavior guidelines:
- If the Responder Identifier TLV is not present, then the node
will behave as a combination egress and branch node.
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- If the Responder Identifier TLV containing a Node Address
sub-TLV is present, and:
- If the address specified in the sub-TLV matches to an address
in the node, then the node will behave like an combination
egress and branch node.
- If the address specified in the sub-TLV does not match any
address in the node, then no response will be sent.
- If the Responder Identifier TLV containing an Egress Address
sub-TLV is present, and:
- If the address specified in the sub-TLV matches to an address
in the node, then the node will behave like an egress node
only.
- If the node lies on the path to the address specified in the
sub-TLV, then the node will behave like a transit node.
- If the node does not lie on the path to the address specified
in the sub-TLV, then no response will be sent.
Once the node behavior has been determined, the possible values for
Return Codes are as follows:
- If the node is behaving as an egress node only, then the Return
Code MAY be set to value 3 ('Replying router is an egress for
the FEC at stack-depth <RSC>') or any other error value as
needed. The echo response MUST NOT contain any Downstream
Detailed Mapping TLV, even if one is present in the echo
request.
- If the node is behaving as a transit node, and:
- If a Downstream Detailed Mapping TLV is not present, then
the Return Code MAY be set to value 8 ('Label switched at
stack-depth <RSC>') or any other error value as needed.
- If a Downstream Detailed Mapping TLV is present, then the
Return Code MAY be set to value TBD ('See DDM TLV for
Return Code and Return SubCode') as defined in [DDMT]. The
Return Code for the Downstream Detailed Mapping TLV will
depend on the downstream path as described in [DDMT].
There will be only one Downstream Detailed Mapping
corresponding to the downstream path to the address
specified in the Egress Address Sub-TLV.
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- If the node is behaving as a combination egress and branch node,
and:
- If a Downstream Detailed Mapping TLV is not present, then
the Return Code MAY be set to value 3 ('Replying router is
an egress for the FEC at stack-depth <RSC>') or any other
error value as needed.
- If a Downstream Detailed Mapping TLV is present, then the
Return Code MAY be set to value 3 ('Replying router is an
egress for the FEC at stack-depth <RSC>') or any other
error value as needed. Return Code for the each Downstream
Detailed Mapping TLV will depend on the downstream path as
described in [DDMT]. There will be a Downstream Detailed
Mapping for each downstream path from the node.
4.3. Special Considerations for Traceroute
4.3.1. End of Processing for Traceroutes
As specified in [RFC4379], the traceroute mode operates by sending a
series of echo requests with sequentially increasing TTL values. For
regular P2P targets, this processing stops when a valid response is
received from the intended egress or when some errored return code is
received.
For P2MP targets, there may not be an easy way to figure out the end
of the traceroute processing, as there are multiple egress nodes.
Receiving a valid response from an egress will not signal the end of
processing.
In P2MP TE LSP, the initiating router has a priori knowledge about
number of egress nodes and their addresses. Hence it possible to
continue processing till a valid response has been received from each
end-point, provided the responses can be matched correctly to the
egress nodes.
However in Multicast LDP LSPs, the initiating router has no knowledge
about the egress nodes. Hence it is not possible to estimate the end
of processing for traceroute in such scenarios.
Therefore it is RECOMMENDED that traceroute operations provide for a
configurable upper limit on TTL values. Hence the user can choose
the depth to which the tree will be probed.
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4.3.2. Multiple responses from Bud and Egress Nodes
The P2MP traceroute may continue even after it has received a valid
response from a bud or egress node, as there may be more nodes at
deeper levels. Hence for subsequent TTL values, a bud or egress node
that has previously replied would continue to get new echo requests.
Since each echo request is handled independently from previous
requests, these bud and egress nodes will keep on responding to the
traceroute echo requests. This can cause extra processing burden for
the initiating router and these bud or egress routers.
To prevent a bud or egress node from sending multiple responses in
the same traceroute operation, a new "Respond Only If TTL Expired"
flag is being introduced. This flag is described in Section 3.4.
It is RECOMMENDED that this flag be used for P2MP traceroute mode
only. By using this flag, extraneous responses from bud and egress
nodes can be reduced. If PHP is being used in the P2MP tree, then
bud and egress nodes will not get any labels with the echo request
packet. Hence this mechanism will not be effective for PHP scenario.
4.3.3. Non-Response to Traceroute Echo Requests
There are multiple reasons for which an ingress node may not receive
a response to its echo request. For example, the transit node has
failed, or the transit node does not support LSP Ping.
When no response to an echo request is received by the ingress, then
as per [RFC4379] the subsequent echo request with a larger TTL SHOULD
be sent.
4.3.4. Use of Downstream Detailed Mapping TLV in Echo Request
As described in section 4.6 of [RFC4379], an initiating router,
during traceroute, SHOULD copy the Downstream Mapping(s) into its
next echo request(s). However for P2MP LSPs, the intiating router
will receive multiple sets of Downstream Detailed Mapping TLV from
different nodes. It is not practical to copy all of them into the
next echo request. Hence this behavior is being modified for P2MP
LSPs. In the echo request packet, the "Downstream IP Address" field,
of the Downstream Detailed Mapping TLV, SHOULD be set to the
ALLROUTERS multicast address.
If an Egress Address Responder Identifier sub-TLV is being used, then
the traceroute is limited to only one path to one egress. Therefore
this traceroute is effectively behaving like a P2P traceroute. In
this scenario, as per section 4.2, the echo responses from
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intermediate nodes will contain only one Downstream Detailed Mapping
TLV corresponding to the downstream path required to reach the
address specified in the Egress Address sub-TLV. For this case, the
echo request packet MAY reuse a received Downstream Detailed Mapping
TLV.
4.3.5 Cross Over Node Processing
A cross-over nodes will require slightly different processing for
traceroute mode. The following definition of cross-over is taken from
[RFC4875].
The term "cross-over" refers to the case of an ingress or transit
node that creates a branch of a P2MP LSP, a cross-over branch, that
intersects the P2MP LSP at another node farther down the tree. It
is unlike re-merge in that, at the intersecting node, the
cross-over branch has a different outgoing interface as well as a
different incoming interface.
During traceroute, a cross-over node will receive the echo requests
via each of its input interfaces. Therefore the Downstream Detailed
Mapping TLV in the echo response SHOULD carry information only about
the outgoing interface corresponding to the input interface.
Due to this restriction, the cross-over node will not duplicate the
outgoing interface information in each of the echo request it
receives via the different input interfaces. This will reflect the
actual packet replication in the data plane.
5. Non-compliant Routers
If a node for a P2MP LSP does not support MPLS LSP ping, then no
reply will be sent, resulting in a "false negative" result. There is
no protection for this situation, and operators may wish to ensure
that all nodes for P2MP LSPs are all equally capable of supporting
this function.
If the non-compliant node is an egress, then the traceroute mode can
be used to verify the LSP nearly all the way to the egress, leaving
the final hop to be verified manually.
If the non-compliant node is a branch or transit node, then it should
not impact ping mode. However the node will not respond during
traceroute mode.
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6. OAM Considerations
The procedures in this document provide OAM functions for P2MP MPLS
LSPs and may be used to enable bootstrapping of other OAM procedures.
In order to be fully operational several considerations must be made.
- Scaling concerns dictate that only cautious use of LSP Ping
should be made. In particular, sending an LSP Ping to all
egresses of a P2MP MPLS LSP could result in congestion at or
near the ingress when the responses arrive.
Further, incautious use of timers to generate LSP Ping echo
requests either in ping mode or especially in traceroute may
lead to significant degradation of network performance.
- Management interfaces should allow an operator full control over
the operation of LSP Ping. In particular, it SHOULD provide the
ability to limit the scope of an LSP Ping echo request for a
P2MP MPLS LSP to a single egress.
Such an interface SHOULD also provide the ability to disable all
active LSP Ping operations to provide a quick escape if the
network becomes congested.
- A MIB module is required for the control and management of LSP
Ping operations, and to enable the reported information to be
inspected.
There is no reason to believe this should not be a simple
extension of the LSP Ping MIB module used for P2P LSPs.
7. IANA Considerations
7.1. New Sub-TLV Types
Four new sub-TLV types are defined for inclusion within the LSP Ping
[RFC4379] Target FEC Stack TLV (TLV type 1).
IANA is requested to assign sub-type values to the following sub-TLVs
from the "Multiprotocol Label Switching Architecture (MPLS) Label
Switched Paths (LSPs) Parameters - TLVs" registry, "TLVs and
sub-TLVs" sub-registry.
RSVP P2MP IPv4 Session (Section 3.1.1). Suggested value 17.
RSVP P2MP IPv6 Session (Section 3.1.1). Suggested value 18.
Multicast P2MP LDP FEC Stack (Section 3.1.2). Suggested value 19.
Multicast MP2MP LDP FEC Stack (Section 3.1.2). Suggested value 20.
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7.2. New TLVs
Two new LSP Ping TLV types are defined for inclusion in LSP Ping
messages.
IANA is requested to assign a new value from the "Multi-Protocol
Label Switching Architecture (MPLS) Label Switched Paths (LSPs)
Parameters - TLVs" registry, "TLVs and sub-TLVs" sub-registry as
follows using a Standards Action value.
P2MP Responder Identifier TLV (see Section 3.2) is a mandatory
TLV. Suggested value 11. Four sub-TLVs are defined.
- Type 1: IPv4 Egress Address P2MP Responder Identifier
- Type 2: IPv6 Egress Address P2MP Responder Identifier
- Type 3: IPv4 Node Address P2MP Responder Identifier
- Type 4: IPv6 Node Address P2MP Responder Identifier
Echo Jitter TLV (see Section 3.3) is a mandatory TLV. Suggested
value 12.
8. Security Considerations
This document does not introduce security concerns over and above
those described in [RFC4379]. Note that because of the scalability
implications of many egresses to P2MP MPLS LSPs, there is a stronger
concern to regulate the LSP Ping traffic passed to the control plane
by the use of a rate limiter applied to the LSP Ping well-known UDP
port. Note that this rate limiting might lead to false positives.
9. Acknowledgements
The authors would like to acknowledge the authors of [RFC4379] for
their work which is substantially re-used in this document. Also
thanks to the members of the MBONED working group for their review of
this material, to Daniel King and Mustapha Aissaoui for their review,
and to Yakov Rekhter for useful discussions.
The authors would like to thank Bill Fenner, Vanson Lim, Danny
Prairie, Reshad Rahman, Ben Niven-Jenkins, Hannes Gredler, Nitin
Bahadur, Tetsuya Murakami, Michael Hua, Michael Wildt, Dipa Thakkar,
Sam Aldrin and IJsbrand Wijnands for their comments and suggestions.
10. References
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10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K., and Swallow, G., "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[DDMT] Bahadur, N., Kompella, K., and Swallow, G., "Mechanism
for Performing LSP-Ping over MPLS Tunnels", draft-ietf-
mpls-lsp-ping-enhanced-dsmap, work in progress.
10.2. Informative References
[RFC792] Postel, J., "Internet Control Message Protocol", RFC 792.
[RFC4461] Yasukawa, S., "Signaling Requirements for Point to
Multipoint Traffic Engineered Multiprotocol Label
Switching (MPLS) Label Switched Paths (LSPs)",
RFC 4461, April 2006.
[RFC4687] Yasukawa, S., Farrel, A., King, D., and Nadeau, T.,
"Operations and Management (OAM) Requirements for
Point-to-Multipoint MPLS Networks", RFC 4687, September
2006.
[RFC4875] Aggarwal, R., Papadimitriou, D., and Yasukawa, S.,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[P2MP-LDP-REQ] J.-L. Le Roux, et al., "Requirements for
point-to-multipoint extensions to the Label Distribution
Protocol", draft-ietf-mpls-mp-ldp-reqs, work in progress.
[P2MP-LDP] Minei, I., and Wijnands, I., "Label Distribution Protocol
Extensions for Point-to-Multipoint and
Multipoint-to-Multipoint Label Switched Paths",
draft-ietf-mpls-ldp-p2mp, work in progress.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and Swallow, G.,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010.
[IANA-PORT] IANA Assigned Port Numbers, http://www.iana.org
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11. Authors' Addresses
Seisho Yasukawa
NTT Corporation
(R&D Strategy Department)
3-1, Otemachi 2-Chome Chiyodaku, Tokyo 100-8116 Japan
Phone: +81 3 5205 5341
Email: yasukawa.seisho@lab.ntt.co.jp
Adrian Farrel
Old Dog Consulting
EMail: adrian@olddog.co.uk
Zafar Ali
Cisco Systems Inc.
2000 Innovation Drive
Kanata, ON, K2K 3E8, Canada.
Phone: 613-889-6158
Email: zali@cisco.com
George Swallow
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
Email: swallow@cisco.com
Thomas D. Nadeau
British Telecom
BT Centre
81 Newgate Street
EC1A 7AJ
London
Email: tom.nadeau@bt.com
Shaleen Saxena
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
Email: ssaxena@cisco.com
12. Full Copyright Statement
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
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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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Saxena, et al. [Page 27]