draft-ietf-mpls-lsp-ping-enhanced-dsmap-11.txt   rfc6424.txt 
Network Working Group N. Bahadur Internet Engineering Task Force (IETF) N. Bahadur
Internet-Draft K. Kompella Request for Comments: 6424 K. Kompella
Updates: 4379 (if approved) Juniper Networks, Inc. Updates: 4379 Juniper Networks, Inc.
Intended status: Standards Track G. Swallow Category: Standards Track G. Swallow
Expires: March 13, 2012 Cisco Systems ISSN: 2070-1721 Cisco Systems
September 10, 2011 November 2011
Mechanism for performing LSP-Ping over MPLS tunnels Mechanism for Performing Label Switched Path Ping (LSP Ping)
draft-ietf-mpls-lsp-ping-enhanced-dsmap-11 over MPLS Tunnels
Abstract Abstract
This document describes methods for performing LSP-Ping (specified in This document describes methods for performing LSP ping (specified in
RFC 4379) traceroute over MPLS tunnels and for traceroute of stitched RFC 4379) traceroute over MPLS tunnels and for traceroute of stitched
MPLS label-switched-paths (LSPs). The techniques outlined in RFC MPLS Label Switched Paths (LSPs). The techniques outlined in RFC
4379 are insufficient to perform traceroute Forwarding Equivalency 4379 are insufficient to perform traceroute Forwarding Equivalency
Class (FEC) validation and path discovery for an LSP that goes over Class (FEC) validation and path discovery for an LSP that goes over
other MPLS tunnels or for a stitched LSP. This document describes other MPLS tunnels or for a stitched LSP. This document deprecates
enhancements to the downstream-mapping TLV (defined in RFC 4379). the Downstream Mapping TLV (defined in RFC 4379) in favor of a new
These enhancements along with other procedures outlined in this TLV that, along with other procedures outlined in this document, can
document can be used to trace such LSPs. be used to trace such LSPs.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on March 13, 2012. 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/rfc6424.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conventions used in this document . . . . . . . . . . . . 4 1.1. Conventions Used in This Document . . . . . . . . . . . . 4
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Packet format . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Summary of Changes . . . . . . . . . . . . . . . . . . . . 5
3.2. New Return Codes . . . . . . . . . . . . . . . . . . . . . 6 3.2. New Return Codes . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. Return code per downstream . . . . . . . . . . . . . . 6 3.2.1. Return Code per Downstream . . . . . . . . . . . . . . 6
3.2.2. Return code for stitched LSPs . . . . . . . . . . . . 6 3.2.2. Return Code for Stitched LSPs . . . . . . . . . . . . 6
3.3. Downstream Detailed Mapping TLV . . . . . . . . . . . . . 7 3.3. Downstream Detailed Mapping TLV . . . . . . . . . . . . . 7
3.3.1. Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . 9 3.3.1. Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.1.1. Multipath data sub-TLV . . . . . . . . . . . . . . 9 3.3.1.1. Multipath Data Sub-TLV . . . . . . . . . . . . . . 9
3.4. Deprecation of Downstream Mapping TLV . . . . . . . . . . 13 3.4. Deprecation of Downstream Mapping TLV . . . . . . . . . . 13
4. Performing MPLS traceroute on tunnels . . . . . . . . . . . . 13 4. Performing MPLS Traceroute on Tunnels . . . . . . . . . . . . 13
4.1. Transit node procedure . . . . . . . . . . . . . . . . . . 13 4.1. Transit Node Procedure . . . . . . . . . . . . . . . . . . 13
4.1.1. Addition of a new tunnel . . . . . . . . . . . . . . . 13 4.1.1. Addition of a New Tunnel . . . . . . . . . . . . . . . 13
4.1.2. Transition between tunnels . . . . . . . . . . . . . . 14 4.1.2. Transition between Tunnels . . . . . . . . . . . . . . 14
4.1.3. Modification to FEC Validation procedure on Transit . 16 4.1.3. Modification to FEC Validation Procedure on Transit . 16
4.2. Modification to FEC Validation procedure on Egress . . . . 16 4.2. Modification to FEC Validation Procedure on Egress . . . . 16
4.3. Ingress node procedure . . . . . . . . . . . . . . . . . . 16 4.3. Ingress Node Procedure . . . . . . . . . . . . . . . . . . 17
4.3.1. Processing Downstream Detailed Mapping TLV . . . . . . 17 4.3.1. Processing Downstream Detailed Mapping TLV . . . . . . 17
4.3.1.1. Stack Change sub-TLV not present . . . . . . . . . 17 4.3.1.1. Stack Change Sub-TLV Not Present . . . . . . . . . 17
4.3.1.2. Stack Change sub-TLV(s) present . . . . . . . . . 17 4.3.1.2. Stack Change Sub-TLV(s) Present . . . . . . . . . 17
4.3.2. Modifications to handling to Return Code 3 reply. . . 19 4.3.2. Modifications to Handling a Return Code 3 Reply. . . . 19
4.3.3. Handling of new return codes . . . . . . . . . . . . . 19 4.3.3. Handling of New Return Codes . . . . . . . . . . . . . 19
4.4. Handling deprecated Downstream Mapping TLV . . . . . . . . 19 4.4. Handling Deprecated Downstream Mapping TLV . . . . . . . . 20
5. Security Considerations . . . . . . . . . . . . . . . . . . . 20 5. Security Considerations . . . . . . . . . . . . . . . . . . . 20
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Normative References . . . . . . . . . . . . . . . . . . . 22 8.1. Normative References . . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . . 22 8.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
This documents describes methods for performing LSP-Ping (specified This documents describes methods for performing LSP ping (specified
in [RFC4379]) traceroute over MPLS tunnels. The techniques in in [RFC4379]) traceroute over MPLS tunnels. The techniques in
[RFC4379] outline a traceroute mechanism that includes Forwarding [RFC4379] outline a traceroute mechanism that includes Forwarding
Equivalency Class (FEC) validation and Equal Cost Multi-Path (ECMP) Equivalency Class (FEC) validation and Equal Cost Multi-Path (ECMP)
path discovery. Those mechanisms are insufficient and do not provide path discovery. Those mechanisms are insufficient and do not provide
details when the FEC being traced traverses one or more MPLS tunnels details when the FEC being traced traverses one or more MPLS tunnels
and when label-switched-path (LSP) stitching [RFC5150] is in use. and when Label Switched Path (LSP) stitching [RFC5150] is in use.
This document defines enhancements to the downstream-mapping TLV This document deprecates the Downstream Mapping TLV [RFC4379],
[RFC4379] to make it more extensible and to enable retrieval of introducing instead a new TLV that is more extensible and that
detailed information. Using the enhanced TLV format along with the enables retrieval of detailed information. Using the new TLV format
existing definitions of [RFC4379], this document describes procedures along with the existing definitions of [RFC4379], this document
by which a traceroute request can correctly traverse MPLS tunnels describes procedures by which a traceroute request can correctly
with proper FEC and label validations. traverse MPLS tunnels with proper FEC and label validations.
1.1. Conventions used in this document 1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Motivation 2. Motivation
A LSP-Ping traceroute may cross multiple MPLS tunnels en-route the An LSP ping traceroute may cross multiple MPLS tunnels en route to
destination. Let us consider a simple case. the destination. Let us consider a simple case.
A B C D E A B C D E
o -------- o -------- o --------- o --------- o o -------- o -------- o --------- o --------- o
\_____/ | \______/ \______/ | \______/ \_____/ | \______/ \______/ | \______/
LDP | RSVP RSVP | LDP LDP | RSVP RSVP | LDP
| | | |
\____________________/ \____________________/
LDP LDP
Figure 1: LDP over RSVP tunnel Figure 1: LDP over RSVP Tunnel
When a traceroute is initiated from router A, router B returns When a traceroute is initiated from router A, router B returns
downstream mapping information for node C in the MPLS echo reply. downstream mapping information for node C in the MPLS echo reply.
The next MPLS echo request reaches router C with a LDP FEC. Node C The next MPLS echo request reaches router C with an LDP FEC. Node C
is a pure RSVP node and does not run LDP. Node C will receive the is a pure RSVP node and does not run LDP. Node C will receive the
MPLS echo request with 2 labels but only 1 FEC in the Target FEC MPLS echo request with two labels but only one FEC in the Target FEC
stack. Consequently, node C will be unable to perform FEC complete stack. Consequently, node C will be unable to perform a complete FEC
validation. It will let the trace continue by just providing next- validation. It will let the trace continue by just providing next-
hop information based on incoming label, and by looking up the hop information based on the incoming label, and by looking up the
forwarding state associated with that label. However, ignoring FEC forwarding state associated with that label. However, ignoring FEC
validation defeats the purpose of control plane validatations. The validation defeats the purpose of control-plane validations. The
MPLS echo request should contain sufficient information to allow node MPLS echo request should contain sufficient information to allow node
C to perform FEC validations to catch any misrouted echo-requests. C to perform FEC validations to catch any misrouted echo requests.
The above problem can be extended for a generic case of hierarchical The above problem can be extended for a generic case of hierarchical
tunnels or stitched tunnels (e.g. B-C can be a separate RSVP tunnel tunnels or stitched tunnels (e.g., B-C can be a separate RSVP tunnel
and C-D can be a separate RSVP tunnel). The problem of FEC and C-D can be a separate RSVP tunnel). The problem of FEC
validation for tunnels can be solved if the transit routers (router B validation for tunnels can be solved if the transit routers (router B
in the above example) provide some information to the ingress in the above example) provide some information to the ingress
regarding the start of a new tunnel. regarding the start of a new tunnel.
Stitched LSPs involve 2 or more LSP segments stitched together. The Stitched LSPs involve two or more LSP segments stitched together.
LSP segments can be signaled using the same or different signaling The LSP segments can be signaled using the same or different
protocols. In order to perform an end-to-end trace of a stitched signaling protocols. In order to perform an end-to-end trace of a
LSP, the ingress needs to know FEC information regarding each of the stitched LSP, the ingress needs to know FEC information regarding
stitched LSP segments. For example, consider the figure below. each of the stitched LSP segments. For example, consider the figure
below.
A B C D E F A B C D E F
o -------- o -------- o --------- o -------- o ------- o o -------- o -------- o --------- o -------- o ------- o
\_____/ \______/ \______/ \______/ \_______/ \_____/ \______/ \______/ \______/ \_______/
LDP LDP BGP RSVP RSVP LDP LDP BGP RSVP RSVP
Figure 2: Stitched LSP Figure 2: Stitched LSP
Consider ingress (A) tracing end-to-end stitched LSP A--F. When an Consider ingress (A) tracing end-to-end stitched LSP A--F. When an
MPLS echo request reaches router C, there is a FEC stack change MPLS echo request reaches router C, there is a FEC stack change
happening at router C. With current LSP-Ping [RFC4379] mechanisms, happening at router C. With current LSP ping [RFC4379] mechanisms,
there is no way to convey this information to A. Consequently, when there is no way to convey this information to A. Consequently, when
the next echo request reaches router D, router D will know nothing the next echo request reaches router D, router D will know nothing
about the LDP FEC that A is trying to trace. about the LDP FEC that A is trying to trace.
Thus, the procedures defined in [RFC4379] do not make it possible for Thus, the procedures defined in [RFC4379] do not make it possible for
the ingress node to: the ingress node to:
1. Know that tunneling has occured 1. Know that tunneling has occurred.
2. Trace the path of the tunnel
3. Trace the path of stitched LSPs
3. Packet format 2. Trace the path of the tunnel.
3.1. Introduction
In many cases there has been a need to associate additional data in 3. Trace the path of stitched LSPs.
the MPLS echo reply. In most cases, the additional data needs to be
associated on a per downstream neighbor basis. Currently, the MPLS 3. Packet Format
echo reply contains one downstream map TLV (DSMAP) per downstream
neighbor. However the DSMAP format is not extensible and hence it is 3.1. Summary of Changes
In many cases, there is a need to associate additional data in the
MPLS echo reply. In most cases, the additional data needs to be
associated on a per-downstream-neighbor basis. Currently, the MPLS
echo reply contains one Downstream Mapping TLV (DSMAP) per downstream
neighbor. However, the DSMAP format is not extensible; hence, it is
not possible to associate more information with a downstream not possible to associate more information with a downstream
neighbor. This draft defines a new extensible format for the DSMAP neighbor. This document defines a new extensible format for the
and provides mechanisms for solving the tunneled LSP-Ping problem DSMAP and provides mechanisms for solving the tunneled LSP ping
using the new format. In summary, the draft makes the following TLV problem using the new format. In summary, this document makes the
changes: following TLV changes:
o Addition of new Downstream Detailed Mapping TLV (DDMAP). o Addition of new Downstream Detailed Mapping TLV (DDMAP).
o Deprecation of existing Downstream Mapping TLV (DSMAP). o Deprecation of existing Downstream Mapping TLV (DSMAP).
o Addition of Downstream FEC Stack Change Sub-TLV to DDMAP.
o Addition of Downstream FEC stack change sub-TLV to DDMAP.
3.2. New Return Codes 3.2. New Return Codes
3.2.1. Return code per downstream 3.2.1. Return Code per Downstream
A new Return Code is being defined "See DDM TLV for Return Code and A new Return Code is being defined "See DDM TLV for Return Code and
Return SubCode" (Section 6.3) to indicate that the Return Code is per Return Subcode" (Section 6.3) to indicate that the Return Code is per
Downstream Detailed Mapping TLV (Section 3.3). This Return Code MUST Downstream Detailed Mapping TLV (Section 3.3). This Return Code MUST
be used only in the message header and MUST be set only in the MPLS be used only in the message header and MUST be set only in the MPLS
echo reply message. If the Return Code is set in the MPLS echo echo reply message. If the Return Code is set in the MPLS echo
request message, then it MUST be ignored. When this Return Code is request message, then it MUST be ignored. When this Return Code is
set, each Downstream Detailed Mapping TLV MUST have an appropriate set, each Downstream Detailed Mapping TLV MUST have an appropriate
Return Code and Return SubCode. This Return Code MUST be used when Return Code and Return Subcode. This Return Code MUST be used when
there are multiple downstreams for a given node (such as P2MP or there are multiple downstreams for a given node (such as Point to
ECMP), and the node needs to return a Return Code/Return SubCode for Multipoint (P2MP) or Equal Cost Multi-Path (ECMP)), and the node
each downstream. This Return Code MAY be used even when there is needs to return a Return Code/Return Subcode for each downstream.
only 1 downstream for a given node. This Return Code MAY be used even when there is only one downstream
for a given node.
3.2.2. Return code for stitched LSPs 3.2.2. Return Code for Stitched LSPs
When a traceroute is being performed on stitched LSPs (Section 4.1.2) When a traceroute is being performed on stitched LSPs
the stitching point SHOULD indicate the stitching action to the node (Section 4.1.2), the stitching point SHOULD indicate the stitching
performing the trace. This is done by setting the Return Code to action to the node performing the trace. This is done by setting the
"Label switched with FEC change" (Section 6.3). If a node is Return Code to "Label switched with FEC change" (Section 6.3). If a
performing FEC hiding, then it MAY choose to set the Return Code to a node is performing FEC hiding, then it MAY choose to set the Return
value (specified in [RFC4379]) other than "Label switched with FEC Code to a value (specified in [RFC4379]) other than "Label switched
change". The Return Code of "Label switched with FEC change" MUST with FEC change". The Return Code "Label switched with FEC change"
NOT be used if no FEC Stack sub-TLV (Section 3.3.1.3) is present in MUST NOT be used if no FEC stack sub-TLV (Section 3.3.1.3) is present
the Downstream Detailed Mapping TLV(s). This new Return Code MAY be in the Downstream Detailed Mapping TLV(s). This new Return Code MAY
used for hierarchical LSPs (for indicating start or end of an outer be used for hierarchical LSPs (for indicating the start or end of an
LSP). outer LSP).
3.3. Downstream Detailed Mapping TLV 3.3. Downstream Detailed Mapping TLV
Type # Value Field Type # Value Field
------ ------------ ------ ------------
TBD Downstream detailed mapping 20 Downstream Detailed Mapping
The Downstream Detailed Mapping object is a TLV that MAY be included The Downstream Detailed Mapping object is a TLV that MAY be included
in an MPLS echo request message. Only one Downstream Detailed in an MPLS echo request message. Only one Downstream Detailed
Mapping object may appear in an echo request. The presence of a Mapping object may appear in an echo request. The presence of a
Downstream Detailed Mapping object is a request that Downstream Downstream Detailed Mapping object is a request that Downstream
Detailed Mapping objects be included in the MPLS echo reply. If the Detailed Mapping objects be included in the MPLS echo reply. If the
replying router is the destination (Label Edge Router) of the FEC, replying router is the destination (Label Edge Router) of the FEC,
then a Downstream Detailed Mapping TLV SHOULD NOT be included in the then a Downstream Detailed Mapping TLV SHOULD NOT be included in the
MPLS echo reply. Otherwise the replying router SHOULD include a MPLS echo reply. Otherwise, the replying router SHOULD include a
Downstream Detailed Mapping object for each interface over which this Downstream Detailed Mapping object for each interface over which this
FEC could be forwarded. FEC could be forwarded.
0 1 2 3 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 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU | Address Type | DS Flags | | MTU | Address Type | DS Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Address (4 or 16 octets) | | Downstream Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Interface Address (4 or 16 octets) | | Downstream Interface Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Code | Return SubCode| Sub-tlv length | | Return Code | Return Subcode| Sub-tlv Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
. List of Sub TLVs . . List of Sub-TLVs .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Downstream Detailed Mapping TLV Figure 3: Downstream Detailed Mapping TLV
The Downstream Detailed Mapping TLV format is derived from the The Downstream Detailed Mapping TLV format is derived from the
Downstream Mapping TLV format. The key change is that variable Downstream Mapping TLV format. The key change is that variable
length and optional fields have been converted into sub-TLVs. The length and optional fields have been converted into sub-TLVs. The
fields have the same use and meaning as in [RFC4379]. A summary of fields have the same use and meaning as in [RFC4379]. A summary of
the fields taken from Downstream Mapping TLV is as below: the fields taken from the Downstream Mapping TLV is as below:
Maximum Transmission Unit (MTU) Maximum Transmission Unit (MTU)
The MTU is the size in octets of the largest MPLS frame (including The MTU is the size in octets of the largest MPLS frame (including
label stack) that fits on the interface to the Downstream LSR. label stack) that fits on the interface to the Downstream Label
Switching Router (LSR).
Address Type Address Type
The Address Type indicates if the interface is numbered or The Address Type indicates if the interface is numbered or
unnumbered. It also determines the length of the Downstream IP unnumbered. It also determines the length of the Downstream IP
Address and Downstream Interface fields. Address and Downstream Interface fields.
DS Flags DS Flags
The DS Flags field is a bit vector of various flags. The DS Flags field is a bit vector of various flags.
Downstream Address and Downstream Interface Address Downstream Address and Downstream Interface Address
IPv4 addresses and interface indices are encoded in 4 octets; IPv6 IPv4 addresses and interface indices are encoded in 4 octets; IPv6
addresses are encoded in 16 octets. For details regarding setting addresses are encoded in 16 octets. For details regarding setting
the address value, refer to [RFC4379]. the address value, refer to [RFC4379].
The newly added sub-TLVs and their fields are as described below. The newly added sub-TLVs and their fields are as described below.
Return code Return Code
The Return Code is set to zero by the sender. The receiver can The Return Code is set to zero by the sender. The receiver can
set it to one of the values specified in the "Multi-Protocol Label set it to one of the values specified in the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Parameters" registry, Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
"Return Codes" sub-registry. registry, "Return Codes" sub-registry.
If the receiver sets a non-zero value of the Return Code field in If the receiver sets a non-zero value of the Return Code field in
the Downstream Detailed Mapping TLV, then the receiver MUST also the Downstream Detailed Mapping TLV, then the receiver MUST also
set the Return Code field in the echo reply header to "See DDM TLV set the Return Code field in the echo reply header to "See DDM TLV
for Return Code and Return SubCode" (Section 6.3). An exception for Return Code and Return Subcode" (Section 6.3). An exception
to this is if the receiver is a bud node [RFC4461] and is replying to this is if the receiver is a bud node [RFC4461] and is replying
as both an egress and a transit node with a Return Code of 3 as both an egress and a transit node with a Return Code of 3
("Replying router is an egress for the FEC") in the echo reply ("Replying router is an egress for the FEC at stack-depth <RSC>")
header. in the echo reply header.
If the Return Code of the echo reply message is not set to either If the Return Code of the echo reply message is not set to either
"See DDM TLV for Return Code and Return SubCode" (Section 6.3) or "See DDM TLV for Return Code and Return Subcode" (Section 6.3) or
"Replying router is an egress for the FEC", then the Return Code "Replying router is an egress for the FEC at stack-depth <RSC>",
specified in the Downstream Detailed Mapping TLV MUST be ignored. then the Return Code specified in the Downstream Detailed Mapping
TLV MUST be ignored.
Return SubCode Return Subcode
The Return SubCode is set to zero by the sender. The receiver can The Return Subcode is set to zero by the sender. The receiver can
set it to one of the values specified in the "Multi-Protocol Label set it to one of the values specified in the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Parameters" registry, Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
"Return Codes" sub-registry. This field is filled in with the registry, "Return Codes" sub-registry. This field is filled in
stack-depth for those codes that specify that. For all other with the stack-depth for those codes that specify the stack-depth.
codes, the Return SubCode MUST be set to zero. For all other codes, the Return Subcode MUST be set to zero.
If the Return Code of the echo reply message is not set to either If the Return Code of the echo reply message is not set to either
"See DDM TLV for Return Code and Return SubCode" (Section 6.3) or "See DDM TLV for Return Code and Return Subcode" (Section 6.3) or
"Replying router is an egress for the FEC", then the Return "Replying router is an egress for the FEC at stack-depth <RSC>",
SubCode specified in the Downstream Detailed Mapping TLV MUST be then the Return Subcode specified in the Downstream Detailed
ignored. Mapping TLV MUST be ignored.
Sub-tlv Length
Sub-tlv length
Total length in bytes of the sub-TLVs associated with this TLV. Total length in bytes of the sub-TLVs associated with this TLV.
3.3.1. Sub-TLVs 3.3.1. Sub-TLVs
This section defines the Sub-TLVs that MAY be included as part of the This section defines the sub-TLVs that MAY be included as part of the
Downstream Detailed Mapping TLV. Downstream Detailed Mapping TLV.
Sub-Type Value Field Sub-Type Value Field
--------- ------------ --------- ------------
TBD Multipath data 1 Multipath data
TBD Label stack 2 Label stack
TBD FEC Stack change 3 FEC stack change
3.3.1.1. Multipath data sub-TLV 3.3.1.1. Multipath Data Sub-TLV
0 1 2 3 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 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Multipath Type | Multipath Length |Reserved (MBZ) | |Multipath Type | Multipath Length |Reserved (MBZ) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| (Multipath Information) | | (Multipath Information) |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Multipath Sub-TLV Figure 4: Multipath Sub-TLV
The multipath data sub-TLV includes multipath information. The sub- The multipath data sub-TLV includes Multipath Information. The sub-
TLV fields and their usage is as defined in [RFC4379]. A brief TLV fields and their usage is as defined in [RFC4379]. A brief
summary of the fields is as below: summary of the fields is as below:
Multipath Type Multipath Type
The type of the encoding for the Multipath Information. The type of the encoding for the Multipath Information.
Multipath Length Multipath Length
The length in octets of the Multipath Information. The length in octets of the Multipath Information.
MBZ
MUST be set to zero when sending; MUST be ignored on receipt.
Multipath Information Multipath Information
Encoded multipath data, according to the Multipath Type. Encoded multipath data, according to the Multipath Type.
3.3.1.2. Label stack sub-TLV 3.3.1.2. Label Stack Sub-TLV
0 1 2 3 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 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol | | Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol | | Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Label Stack Sub-TLV Figure 5: Label Stack Sub-TLV
The Label stack sub-TLV contains the set of labels in the label stack The Label stack sub-TLV contains the set of labels in the label stack
as it would have appeared if this router were forwarding the packet as it would have appeared if this router were forwarding the packet
through this interface. Any Implicit Null labels are explicitly through this interface. Any Implicit Null labels are explicitly
included. The number of label/protocol pairs present in the sub-TLV included. The number of label/protocol pairs present in the sub-TLV
is determined based on the sub-TLV data length. The label format and is determined based on the sub-TLV data length. The label format and
protocol type are as defined in [RFC4379]. When the Downstream protocol type are as defined in [RFC4379]. When the Downstream
Detailed Mapping TLV is sent in the echo reply, this sub-TLV MUST be Detailed Mapping TLV is sent in the echo reply, this sub-TLV MUST be
included. included.
Downstream Label Downstream Label
A Downstream Label is 24 bits, in the same format as an MPLS label A Downstream label is 24 bits, in the same format as an MPLS label
minus the TTL field, i.e., the MSBit of the label is bit 0, the minus the Time to Live (TTL) field, i.e., the MSBit of the label
LSBit is bit 19, the EXP bits are bits 20-22, and bit 23 is the S is bit 0, the LSBit is bit 19, the Traffic Class (TC) field
bit. The replying router SHOULD fill in the EXP and S bits; the [RFC5462] is bits 20-22, and S is bit 23. The replying router
LSR receiving the echo reply MAY choose to ignore these bits. SHOULD fill in the TC field and S bit; the LSR receiving the echo
reply MAY choose to ignore these.
Protocol Protocol
This specifies the label distribution protocol for the downstream
This specifies the label distribution protocol for the Downstream
label. label.
3.3.1.3. FEC Stack change sub-TLV 3.3.1.3. FEC Stack Change Sub-TLV
A router MUST include the FEC Stack change sub-TLV when the A router MUST include the FEC stack change sub-TLV when the
downstream node in the echo reply has a different FEC Stack than the downstream node in the echo reply has a different FEC Stack than the
FEC stack received in the echo request. One or more FEC Stack change FEC Stack received in the echo request. One or more FEC stack change
sub-TLVs MAY be present in the Downstream Detailed Mapping TLV. The sub-TLVs MAY be present in the Downstream Detailed Mapping TLV. The
format is as below. format is as below.
0 1 2 3 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 2 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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Operation Type | Address type | FEC-tlv length| Reserved | |Operation Type | Address Type | FEC-tlv length| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Peer Address (0, 4 or 16 octets) | | Remote Peer Address (0, 4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
. FEC TLV . . FEC TLV .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: FEC Stack Change Sub-TLV Figure 6: FEC Stack Change Sub-TLV
Operation Type Operation Type
The operation type specifies the action associated with the FEC The operation type specifies the action associated with the FEC
stack change. The following operation types are defined. stack change. The following operation types are defined:
Type # Operation Type # Operation
------ --------- ------ ---------
1 Push 1 Push
2 Pop 2 Pop
Address Type Address Type
The Address Type indicates the remote peer's address type. The The Address Type indicates the remote peer's address type. The
Address Type is set to one of the following values. The peer Address Type is set to one of the following values. The length of
address length is determined based on the address type. The the peer address is determined based on the address type. The
address type MAY be different from the address type included in address type MAY be different from the address type included in
the Downstream Detailed Mapping TLV. This can happen when the LSP the Downstream Detailed Mapping TLV. This can happen when the LSP
goes over a tunnel of a different address family. The address goes over a tunnel of a different address family. The address
type MAY be set to Unspecified if the peer-address is either type MAY be set to Unspecified if the peer address is either
unavailable or the transit router does not wish it provide it for unavailable or the transit router does not wish to provide it for
security or administrative reasons. security or administrative reasons.
Type # Address Type Address length Type # Address Type Address length
------ ------------ -------------- ------ ------------ --------------
0 Unspecified 0 0 Unspecified 0
1 IPv4 4 1 IPv4 4
2 IPv6 16 2 IPv6 16
FEC tlv Length FEC TLV Length
Length in bytes of the FEC TLV. Length in bytes of the FEC TLV.
Reserved Reserved
This field is reserved for future use and MUST be set to zero. This field is reserved for future use and MUST be set to zero.
Remote peer address Remote Peer Address
The remote peer address specifies the remote peer which is the The remote peer address specifies the remote peer that is the
next-hop for the FEC being currently traced. E.g. in the LDP over next-hop for the FEC being currently traced. For example, in the
RSVP case Figure 1, router B would respond back with the address LDP over RSVP case in Figure 1, router B would respond back with
of router D as the remote peer address for the LDP FEC being the address of router D as the remote peer address for the LDP FEC
traced. This allows the ingress node to provide information being traced. This allows the ingress node to provide information
regarding FEC peers. If the operation type is PUSH, the remote regarding FEC peers. If the operation type is PUSH, the remote
peer address is the address of the peer from which the FEC being peer address is the address of the peer from which the FEC being
pushed was learnt. If the operation type is POP, the remote peer pushed was learned. If the operation type is POP, the remote peer
address MAY be set to Unspecified. address MAY be set to Unspecified.
For upstream assigned labels [RFC5331], an operation type of POP
For upstream-assigned labels [RFC5331], an operation type of POP
will have a remote peer address (the upstream node that assigned will have a remote peer address (the upstream node that assigned
the label) and this SHOULD be included in the FEC Stack change the label) and this SHOULD be included in the FEC stack change
sub-TLV. The remote peer address MAY be set to Unspecified, if sub-TLV. The remote peer address MAY be set to Unspecified if the
the address needs to be hidden. address needs to be hidden.
FEC TLV FEC TLV
The FEC TLV is present only when FEC-tlv length field is non-zero.
The FEC TLV specifies the FEC associated with the FEC stack change
operation. This TLV MAY be included when the operation type is
POP. It MUST be included when the operation type is PUSH. The
FEC TLV contains exactly 1 FEC from the list of FECs specified in
[RFC4379]. A NIL FEC MAY be associated with a PUSH operation if
the responding router wishes to hide the details of the FEC being
pushed.
FEC Stack change sub-TLV operation rules: The FEC TLV is present only when the FEC-tlv length field is non-
zero. The FEC TLV specifies the FEC associated with the FEC stack
change operation. This TLV MAY be included when the operation
type is POP. It MUST be included when the operation type is PUSH.
The FEC TLV contains exactly one FEC from the list of FECs
specified in [RFC4379]. A Nil FEC MAY be associated with a PUSH
operation if the responding router wishes to hide the details of
the FEC being pushed.
a. A FEC Stack change sub-TLV containing a PUSH operation MUST NOT FEC stack change sub-TLV operation rules are as follows:
be followed by a FEC Stack change sub-TLV containing a POP
a. A FEC stack change sub-TLV containing a PUSH operation MUST NOT
be followed by a FEC stack change sub-TLV containing a POP
operation. operation.
b. One or more POP operations MAY be followed by one or more PUSH b. One or more POP operations MAY be followed by one or more PUSH
operations. operations.
c. One FEC Stack change sub-TLV MUST be included per FEC stack
change. For example, if 2 labels are going to be pushed, then 1 c. One FEC stack change sub-TLV MUST be included per FEC stack
FEC Stack change sub-TLV MUST be included for each FEC. change. For example, if 2 labels are going to be pushed, then
d. A FEC splice operation (an operation where 1 FEC ends and another one FEC stack change sub-TLV MUST be included for each FEC.
FEC starts, see Figure 7) MUST be performed by including a POP
type FEC Stack change sub-TLV followed by a PUSH type FEC Stack d. A FEC splice operation (an operation where one FEC ends and
change sub-TLV. another FEC starts, see Figure 7) MUST be performed by including
e. A Downstream detailed mapping TLV containing only 1 FEC Stack a POP type FEC stack change sub-TLV followed by a PUSH type FEC
Change sub-TLV with Pop operation is equivalent to IS_EGRESS stack change sub-TLV.
(Return code 3, [RFC4379]) for the outermost FEC in the FEC
e. A Downstream detailed mapping TLV containing only one FEC stack
change sub-TLV with Pop operation is equivalent to IS_EGRESS
(Return Code 3, [RFC4379]) for the outermost FEC in the FEC
stack. The ingress router performing the MPLS traceroute MUST stack. The ingress router performing the MPLS traceroute MUST
treat such a case as an IS_EGRESS for the outermost FEC. treat such a case as an IS_EGRESS for the outermost FEC.
3.4. Deprecation of Downstream Mapping TLV 3.4. Deprecation of Downstream Mapping TLV
This document deprecates the Downstream Mapping TLV. LSP-ping This document deprecates the Downstream Mapping TLV. LSP ping
procedures should now use the Downstream Detailed Mapping TLV. procedures should now use the Downstream Detailed Mapping TLV.
Detailed procedures regarding interoperability between the deprecated Detailed procedures regarding interoperability between the deprecated
TLV and the new TLV are specified in Section 4.4. TLV and the new TLV are specified in Section 4.4.
4. Performing MPLS traceroute on tunnels 4. Performing MPLS Traceroute on Tunnels
This section describes the procedures to be followed by an LSP This section describes the procedures to be followed by an LSP
ingress node and LSP transit nodes when performing MPLS traceroute ingress node and LSP transit nodes when performing MPLS traceroute
over MPLS tunnels. over MPLS tunnels.
4.1. Transit node procedure 4.1. Transit Node Procedure
4.1.1. Addition of a new tunnel 4.1.1. Addition of a New Tunnel
A transit node (Figure 1) knows when the FEC being traced is going to A transit node (Figure 1) knows when the FEC being traced is going to
enter a tunnel at that node. Thus, it knows about the new outer FEC. enter a tunnel at that node. Thus, it knows about the new outer FEC.
All transit nodes that are the origination point of a new tunnel All transit nodes that are the origination point of a new tunnel
SHOULD add the a FEC Stack change sub-TLV (Section 3.3.1.3) to the SHOULD add the FEC stack change sub-TLV (Section 3.3.1.3) to the
Downstream Detailed Mapping TLV (Figure 3) in the echo reply. The Downstream Detailed Mapping TLV (Figure 3) in the echo reply. The
transit node SHOULD add 1 FEC Stack change sub-TLV of operation type transit node SHOULD add one FEC stack change sub-TLV of operation
PUSH, per new tunnel being originated at the transit node. type PUSH, per new tunnel being originated at the transit node.
A transit node that sends a Downstream FEC Stack change sub-TLV in A transit node that sends a Downstream FEC stack change sub-TLV in
the echo reply SHOULD fill the address of the remote peer; which is the echo reply SHOULD fill the address of the remote peer; which is
the peer of the current LSP being traced. If the transit node does the peer of the current LSP being traced. If the transit node does
not know the address of the remote peer, it MUST set the address type not know the address of the remote peer, it MUST set the address type
to Unspecified. to Unspecified.
The Label stack sub-TLV MUST contain 1 additional label per FEC being The Label stack sub-TLV MUST contain one additional label per FEC
PUSHed. The label MUST be encoded as per Figure 5. The label value being PUSHed. The label MUST be encoded as per Figure 5. The label
MUST be the value used to switch the data traffic. If the tunnel is value MUST be the value used to switch the data traffic. If the
transparent pipe to the node, i.e. the data-plane trace will not tunnel is a transparent pipe to the node, i.e. the data-plane trace
expire in the middle of the new tunnel, then a FEC Stack change sub- will not expire in the middle of the new tunnel, then a FEC stack
TLV SHOULD NOT be added and the Label stack sub-TLV SHOULD NOT change sub-TLV SHOULD NOT be added and the Label stack sub-TLV SHOULD
contain a label corresponding to the hidden tunnel. NOT contain a label corresponding to the hidden tunnel.
If the transit node wishes to hide the nature of the tunnel from the If the transit node wishes to hide the nature of the tunnel from the
ingress of the echo request, then it MAY not want to send details ingress of the echo request, then it MAY not want to send details
about the new tunnel FEC to the ingress. In such a case, the transit about the new tunnel FEC to the ingress. In such a case, the transit
node SHOULD use the NIL FEC. The echo reply would then contain a FEC node SHOULD use the Nil FEC. The echo reply would then contain a FEC
Stack change sub-TLV with operation type PUSH and a NIL FEC. The stack change sub-TLV with operation type PUSH and a Nil FEC. The
value of the label in the NIL FEC MUST be set to zero. The remote value of the label in the Nil FEC MUST be set to zero. The remote
peer address type MUST be set to Unspecified. The transit node peer address type MUST be set to Unspecified. The transit node
SHOULD add 1 FEC Stack change sub-TLV of operation type PUSH, per new SHOULD add one FEC stack change sub-TLV of operation type PUSH, per
tunnel being originated at the transit node. The Label stack sub-TLV new tunnel being originated at the transit node. The Label stack
MUST contain 1 additional label per FEC being PUSHed. The label sub-TLV MUST contain one additional label per FEC being PUSHed. The
value MUST be the value used to switch the data traffic. label value MUST be the value used to switch the data traffic.
4.1.2. Transition between tunnels 4.1.2. Transition between Tunnels
A B C D E F A B C D E F
o -------- o -------- o --------- o -------- o ------- o o -------- o -------- o --------- o -------- o ------- o
\_____/ \______/ \______/ \______/ \_______/ \_____/ \______/ \______/ \______/ \_______/
LDP LDP BGP RSVP RSVP LDP LDP BGP RSVP RSVP
Figure 7: Stitched LSPs Figure 7: Stitched LSPs
In the above figure, we have 3 seperate LSP segments stitched at C In the above figure, we have three separate LSP segments stitched at
and D. Node C SHOULD include 2 FEC Stack change sub-TLVs. One with a C and D. Node C SHOULD include two FEC stack change sub-TLVs. One
POP operation for the LDP FEC and one with the PUSH operation for the with a POP operation for the LDP FEC and one with the PUSH operation
BGP FEC. Similarly, node D SHOULD include 2 FEC Stack change sub- for the BGP FEC. Similarly, node D SHOULD include two FEC stack
TLVs, one with a POP operation for the BGP FEC and one with a PUSH change sub-TLVs, one with a POP operation for the BGP FEC and one
operation for the RSVP FEC. Nodes C and D SHOULD set the Return Code with a PUSH operation for the RSVP FEC. Nodes C and D SHOULD set the
to "Label switched with FEC change" (Section 6.3) to indicate change Return Code to "Label switched with FEC change" (Section 6.3) to
in FEC being traced. indicate change in FEC being traced.
If node C wishes to perform FEC hiding, it SHOULD respond back with 2 If node C wishes to perform FEC hiding, it SHOULD respond back with
FEC Stack change sub-TLVs. One POP followed by 1 PUSH. The POP two FEC stack change sub-TLVs, one POP followed by one PUSH. The POP
operation MAY either exclude the FEC TLV (by setting FEC TLV length operation MAY either exclude the FEC TLV (by setting the FEC TLV
to 0) or set the FEC TLV to contain the LDP FEC. The PUSH operation length to 0) or set the FEC TLV to contain the LDP FEC. The PUSH
SHOULD have the FEC TLV containing the NIL FEC. The Return Code operation SHOULD have the FEC TLV containing the Nil FEC. The Return
SHOULD be set to "Label switched with FEC change". Code SHOULD be set to "Label switched with FEC change".
If node C performs FEC hiding and node D also performs FEC hiding, If node C performs FEC hiding and node D also performs FEC hiding,
then node D MAY choose to not send any FEC Stack change sub-TLVs in then node D MAY choose to not send any FEC stack change sub-TLVs in
the echo reply since the number of labels has not changed (for the the echo reply since the number of labels has not changed (for the
downstream of node D) and the FEC type also has not changed (NIL downstream of node D) and the FEC type also has not changed (Nil
FEC). In such a case, node D MUST NOT set the Return Code to "Label FEC). In such a case, node D MUST NOT set the Return Code to "Label
switched with FEC change". If node D performs FEC hiding, then node switched with FEC change". If node D performs FEC hiding, then node
F will respond as IS_EGRESS for the NIL FEC. The ingress (node A) F will respond as IS_EGRESS for the Nil FEC. The ingress (node A)
will know that IS_EGRESS corresponds to the end-to-end LSP. will know that IS_EGRESS corresponds to the end-to-end LSP.
A B C D E F A B C D E F
o -------- o -------- o --------- o --------- o --------- o o -------- o -------- o --------- o --------- o --------- o
\_____/ |\____________________/ |\_______/ \_____/ |\____________________/ |\_______/
LDP |\ RSVP-A | LDP LDP |\ RSVP-A | LDP
| \_______________________________/| | \_______________________________/|
| RSVP-B | | RSVP-B |
\________________________________/ \________________________________/
LDP LDP
Figure 8: Hierarchical LSPs Figure 8: Hierarchical LSPs
In the above figure, we have an end-to-end LDP LSP between nodes A In the above figure, we have an end-to-end LDP LSP between nodes A
and F. The LDP LSP goes over RSVP LSP RSVP-B. LSP RSVP-B itself goes and F. The LDP LSP goes over RSVP LSP RSVP-B. LSP RSVP-B itself
over another RSVP LSP RSVP-A. When node A initiates a traceroute for goes over another RSVP LSP RSVP-A. When node A initiates a
the end-to-end LDP LSP, then following sequence of FEC Stack change traceroute for the end-to-end LDP LSP, then following sequence of FEC
sub-TLVs will be performed stack change sub-TLVs will be performed
Node B: Node B:
Respond with 2 FEC Stack change sub-TLVs: PUSH RSVP-B, PUSH RSVP-A. Respond with two FEC stack change sub-TLVs: PUSH RSVP-B, PUSH RSVP-A.
Node D: Node D:
Respond with a Return Code of 3 when RSVP-A is top of FEC stack. Respond with Return Code 3 when RSVP-A is the top of FEC stack. When
When the echo request contains RSVP-B as top of stack, respond with the echo request contains RSVP-B as top of stack, respond with
Downstream information for node E and an appropriate Return Code. Downstream information for node E and an appropriate Return Code.
If node B is performing tunnel hiding, then: If node B is performing tunnel hiding, then:
Node B: Node B:
Respond with 2 FEC Stack change sub-TLVs: PUSH NIL-FEC, PUSH NIL-FEC. Respond with two FEC stack change sub-TLVs: PUSH Nil FEC, PUSH Nil
FEC.
Node D: Node D:
If D can co-relate that the NIL-FEC corresponds to RSVP-A, which If D determines that the Nil FEC corresponds to RSVP-A, which
terminates at D, then it SHOULD Respond with Return Code of 3. D can terminates at D, then it SHOULD respond with Return Code 3. D can
also respond with FEC Stack change sub-TLV: POP (since D knows that also respond with FEC stack change sub-TLV: POP (since D knows that
number of labels towards next-hop is decreasing). Both responses number of labels towards next-hop is decreasing). Both responses
would be valid. would be valid.
A B C D E F G A B C D E F G
o -------- o -------- o ------ o ------ o ----- o ----- o o -------- o -------- o ------ o ------ o ----- o ----- o
LDP LDP BGP \ RSVP RSVP / LDP LDP LDP BGP \ RSVP RSVP / LDP
\_____________/ \_____________/
LDP LDP
Figure 9: Stitched hierarchical LSPs Figure 9: Stitched Hierarchical LSPs
In the above case, node D will send 3 FEC Stack change sub-TLVs. One In the above case, node D will send three FEC stack change sub-TLVs.
POP (for the BGP FEC) followed by 2 PUSHes (one for LDP and one for One POP (for the BGP FEC) followed by two PUSHes (one for LDP and one
RSVP). Nodes C and D SHOULD set the Return Code to "Label switched for RSVP). Nodes C and D SHOULD set the Return Code to "Label
with FEC change" (Section 6.3) to indicate change in FEC being switched with FEC change" (Section 6.3) to indicate change in FEC
traced. being traced.
4.1.3. Modification to FEC Validation procedure on Transit 4.1.3. Modification to FEC Validation Procedure on Transit
Section 4.4 of [RFC4379] specifies Target FEC stack validation Section 4.4 of [RFC4379] specifies Target FEC stack validation
procedures. This document enhances the FEC validation procedures as procedures. This document enhances the FEC validation procedures as
follows. If the outermost FEC of the target FEC stack is the NIL follows. If the outermost FEC of the target FEC stack is the Nil
FEC, then the node MUST skip the target FEC validation completely. FEC, then the node MUST skip the target FEC validation completely.
This is to support FEC hiding, in which the outer hidden FEC can be This is to support FEC hiding, in which the outer hidden FEC can be
the NIL FEC. the Nil FEC.
4.2. Modification to FEC Validation procedure on Egress 4.2. Modification to FEC Validation Procedure on Egress
Section 4.4 of [RFC4379] specifies Target FEC stack validation Section 4.4 of [RFC4379] specifies Target FEC stack validation
procedures. This document enhances the FEC validation procedures as procedures. This document enhances the FEC validation procedures as
follows. If the outermost FEC of the target FEC stack is the NIL follows. If the outermost FEC of the Target FEC stack is the Nil
FEC, then the node MUST skip the target FEC validation completely. FEC, then the node MUST skip the target FEC validation completely.
This is to support FEC hiding, in which the outer hidden FEC can be This is to support FEC hiding, in which the outer hidden FEC can be
the NIL FEC. the Nil FEC.
4.3. Ingress node procedure 4.3. Ingress Node Procedure
It is the responsibility of an ingress node to understand tunnel It is the responsibility of an ingress node to understand tunnel
within tunnel semantics and LSP stitching semantics when performing a within tunnel semantics and LSP stitching semantics when performing a
MPLS traceroute. This section describes the ingress node procedure MPLS traceroute. This section describes the ingress node procedure
based on the kind of reply an ingress node receives from a transit based on the kind of reply an ingress node receives from a transit
node. node.
4.3.1. Processing Downstream Detailed Mapping TLV 4.3.1. Processing Downstream Detailed Mapping TLV
Downstream Detailed Mapping TLV should be processed in the same way Downstream Detailed Mapping TLV should be processed in the same way
as the Downstream Mapping TLV, defined in Section 4.4 of [RFC4379]. as the Downstream Mapping TLV, defined in Section 4.4 of [RFC4379].
This section describes the procedures for processing the new elements This section describes the procedures for processing the new elements
introduced in this document. introduced in this document.
4.3.1.1. Stack Change sub-TLV not present 4.3.1.1. Stack Change Sub-TLV Not Present
This would be the default behavior as described in [RFC4379]. The This would be the default behavior as described in [RFC4379]. The
ingress node MUST perform MPLS echo reply processing as per the ingress node MUST perform MPLS echo reply processing as per the
procedures in [RFC4379]. procedures in [RFC4379].
4.3.1.2. Stack Change sub-TLV(s) present 4.3.1.2. Stack Change Sub-TLV(s) Present
If one or more FEC Stack change sub-TLVs (Section 3.3.1.3) are If one or more FEC stack change sub-TLVs (Section 3.3.1.3) are
received in the MPLS echo reply, the ingress node SHOULD process them received in the MPLS echo reply, the ingress node SHOULD process them
and perform some validation. and perform some validation.
The FEC stack changes are associated with a downstream neighbor and The FEC stack changes are associated with a downstream neighbor and
along a particular path of the LSP. Consequently, the ingress will along a particular path of the LSP. Consequently, the ingress will
need to maintain a FEC-stack per path being traced (in case of need to maintain a FEC stack per path being traced (in case of
multipath). All changes to the FEC stack resulting from the multipath). All changes to the FEC stack resulting from the
processing of FEC Stack change sub-TLV(s) should be applied only for processing of FEC stack change sub-TLV(s) should be applied only for
the path along a given downstream neighbor. The following algorithm the path along a given downstream neighbor. The following algorithm
should be followed for processing FEC Stack change sub-TLVs. should be followed for processing FEC stack change sub-TLVs.
push_seen = FALSE push_seen = FALSE
fec_stack_depth = current-depth-of-fec-stack-being-traced fec_stack_depth = current-depth-of-fec-stack-being-traced
saved_fec_stack = current_fec_stack saved_fec_stack = current_fec_stack
while (sub-tlv = get_next_sub_tlv(downstream_detailed_map_tlv)) while (sub-tlv = get_next_sub_tlv(downstream_detailed_map_tlv))
if (sub-tlv == NULL) break if (sub-tlv == NULL) break
if (sub-tlv.type == FEC-Stack-Change) { if (sub-tlv.type == FEC-Stack-Change) {
skipping to change at page 18, line 49 skipping to change at page 19, line 6
if (fec_stack_depth == 0) { if (fec_stack_depth == 0) {
Drop the echo reply Drop the echo reply
current_fec_stack = saved_fec_stack current_fec_stack = saved_fec_stack
return return
} }
Figure 10: FEC Stack Change Sub-TLV Processing Guideline Figure 10: FEC Stack Change Sub-TLV Processing Guideline
The next MPLS echo request along the same path should use the The next MPLS echo request along the same path should use the
modified FEC stack obtained after processing the FEC Stack change modified FEC stack obtained after processing the FEC stack change
sub-TLVs. A non-NIL FEC guarantees that the next echo request along sub-TLVs. A non-Nil FEC guarantees that the next echo request along
the same path will have the Downstream Detailed Mapping TLV validated the same path will have the Downstream Detailed Mapping TLV validated
for IP address, Interface address and label stack mismatches. for IP address, Interface address, and label stack mismatches.
If the top of the FEC stack is a NIL FEC and the MPLS echo reply does If the top of the FEC stack is a Nil FEC and the MPLS echo reply does
not contain any FEC Stack change sub-TLV, then it does not not contain any FEC stack change sub-TLVs, then it does not
necessarily mean that the LSP has not started traversing a different necessarily mean that the LSP has not started traversing a different
tunnel. It could be that the LSP associated with the NIL FEC tunnel. It could be that the LSP associated with the Nil FEC
terminated at a transit node and at the same time a new LSP started terminated at a transit node and at the same time a new LSP started
at the same transit node. The NIL FEC would now be associated with at the same transit node. The Nil FEC would now be associated with
the new LSP (and the ingress has no way of knowing this). Thus, it the new LSP (and the ingress has no way of knowing this). Thus, it
is not possible to build an accurate hierarchical LSP topology if a is not possible to build an accurate hierarchical LSP topology if a
traceroute contains NIL FECs. traceroute contains Nil FECs.
4.3.2. Modifications to handling to Return Code 3 reply. 4.3.2. Modifications to Handling a Return Code 3 Reply.
The procedures above allow the addition of new FECs to the original The procedures above allow the addition of new FECs to the original
FEC being traced. Consequently, a reply from a downstream node with FEC being traced. Consequently, a reply from a downstream node with
Return Code of 3 (IS_EGRESS) may not necessarily be for the FEC being Return Code 3 (IS_EGRESS) may not necessarily be for the FEC being
traced. It could be for one of the new FECs that was added. On traced. It could be for one of the new FECs that was added. On
receipt of an IS_EGRESS reply, the LSP ingress should check if the receipt of an IS_EGRESS reply, the LSP ingress should check if the
depth of Target FEC sent to the node that just responded, was the depth of Target FEC sent to the node that just responded, was the
same as the depth of the FEC that was being traced. If it was not, same as the depth of the FEC that was being traced. If it was not,
then it should pop an entry from the Target FEC stack and resend the then it should pop an entry from the Target FEC stack and resend the
request with the same TTL (as previously sent). The process of request with the same TTL (as previously sent). The process of
popping a FEC is to be repeated until either the LSP ingress receives popping a FEC is to be repeated until either the LSP ingress receives
a non-IS_EGRESS reply or until all the additional FECs added to the a non-IS_EGRESS reply or until all the additional FECs added to the
FEC stack have already been popped. Using IS_EGRESS reply, an FEC stack have already been popped. Using an IS_EGRESS reply, an
ingress can build a map of the hierarchical LSP structure traversed ingress can build a map of the hierarchical LSP structure traversed
by a given FEC. by a given FEC.
4.3.3. Handling of new return codes 4.3.3. Handling of New Return Codes
When the MPLS echo reply Return Code is "Label switched with FEC When the MPLS echo reply Return Code is "Label switched with FEC
change" (Section 3.2.2), the ingress node SHOULD manipulate the FEC change" (Section 3.2.2), the ingress node SHOULD manipulate the FEC
stack as per the FEC Stack change sub-TLVs contained in the stack as per the FEC stack change sub-TLVs contained in the
downstream detailed mapping TLV. A transit node can use this Return downstream detailed mapping TLV. A transit node can use this Return
Code for stitched LSPs and for hierarchical LSPs. In case of Equal Code for stitched LSPs and for hierarchical LSPs. In case of ECMP or
Cost Multi-Path (ECMP) or Point to Multi-Point (P2MP), there could be P2MP, there could be multiple paths and Downstream Detailed Mapping
multiple paths and downstream detailed mapping TLVs with different TLVs with different Return Codes (Section 3.2.1). The ingress node
return codes (Section 3.2.1). The ingress node should build the should build the topology based on the Return Code per ECMP path/P2MP
topology based on the Return Code per ECMP path/P2MP branch. branch.
4.4. Handling deprecated Downstream Mapping TLV 4.4. Handling Deprecated Downstream Mapping TLV
The Downstream Mapping TLV has been deprecated. Applications should The Downstream Mapping TLV has been deprecated. Applications should
now use the Downstream Detailed Mapping TLV. The following now use the Downstream Detailed Mapping TLV. The following
procedures SHOULD be used for backward compatibility with routers procedures SHOULD be used for backward compatibility with routers
that do not support the Downstream Detailed Mapping TLV. that do not support the Downstream Detailed Mapping TLV.
o The Downstream Mapping TLV and the Downstream Detailed Mapping TLV o The Downstream Mapping TLV and the Downstream Detailed Mapping TLV
MUST never be sent together in the same MPLS echo request or in MUST never be sent together in the same MPLS echo request or in
the same MPLS echo reply. the same MPLS echo reply.
o If the echo request contains a Downstream Detailed Mapping TLV and o If the echo request contains a Downstream Detailed Mapping TLV and
the corresponding echo reply contains a Return Code of 2 (one or the corresponding echo reply contains a Return Code 2 ("One or
more of the TLVs was not understood), then the sender of the echo more of the TLVs was not understood"), then the sender of the echo
request MAY resend the echo request with the Downstream Mapping request MAY resend the echo request with the Downstream Mapping
TLV (instead of the Downstream Detailed Mapping TLV). In cases TLV (instead of the Downstream Detailed Mapping TLV). In cases
where a detailed reply is needed, the sender can choose to ignore where a detailed reply is needed, the sender can choose to ignore
the router that does not support the Downstream Detailed Mapping the router that does not support the Downstream Detailed Mapping
TLV. TLV.
o If the echo request contains a Downstream Mapping TLV, then a o If the echo request contains a Downstream Mapping TLV, then a
Downstream Detailed Mapping TLV MUST NOT be sent in the echo Downstream Detailed Mapping TLV MUST NOT be sent in the echo
reply. This is to handle the case that the sender of the echo reply. This is to handle the case that the sender of the echo
request does not support the new TLV. The echo reply MAY contain request does not support the new TLV. The echo reply MAY contain
Downstream Mapping TLV(s). Downstream Mapping TLV(s).
o If echo request forwarding is in use; such that the echo request
is processed at an intermediate label switched router (LSR) and o If echo request forwarding is in use (such that the echo request
then forwarded on; then the intermediate router is responsible for is processed at an intermediate LSR and then forwarded on), then
making sure that the TLVs being used among the ingress, the intermediate router is responsible for making sure that the
intermediate and destination are consistent. The intermediate TLVs being used among the ingress, intermediate and destination
router MUST NOT forward an echo request or an echo reply are consistent. The intermediate router MUST NOT forward an echo
containing a Downstream Detailed Mapping TLV if it itself does not request or an echo reply containing a Downstream Detailed Mapping
support that TLV. TLV if it itself does not support that TLV.
5. Security Considerations 5. Security Considerations
1. If a network operator wants to prevent tracing inside a tunnel, 1. If a network operator wants to prevent tracing inside a tunnel,
one can use the pipe mode [RFC3443], i.e. hide the outer MPLS one can use the Pipe Model [RFC3443], i.e., hide the outer MPLS
tunnel by not propagating the MPLS TTL into the outer tunnel (at tunnel by not propagating the MPLS TTL into the outer tunnel (at
the start of the outer tunnel). By doing this, MPLS traceroute the start of the outer tunnel). By doing this, MPLS traceroute
packets will not expire in the outer tunnel and the outer tunnel packets will not expire in the outer tunnel and the outer tunnel
will not get traced. will not get traced.
2. If one doesn't wish to expose the details of the new outer LSP, 2. If one doesn't wish to expose the details of the new outer LSP,
then the NIL FEC can be used to hide those details. Using the then the Nil FEC can be used to hide those details. Using the
NIL FEC ensures that the trace progresses without false negatives Nil FEC ensures that the trace progresses without false negatives
and all transit nodes (of the new outer tunnel) perform some and all transit nodes (of the new outer tunnel) perform some
minimal validations on the received MPLS echo requests. minimal validations on the received MPLS echo requests.
Other security considerations, as discussed in [RFC4379] are also Other security considerations, as discussed in [RFC4379], are also
applicable to this document. applicable to this document.
6. IANA Considerations 6. IANA Considerations
The suggested values in all sub-sections below have been allocated
according to the early allocation process.
6.1. New TLV 6.1. New TLV
IANA is requested to assign TLV type value to the following TLV from IANA has assigned a TLV type value to the following TLV from the
the "Multiprotocol Label Switching Architecture (MPLS) Label Switched "Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub- Paths (LSPs) Ping Parameters" registry, "TLVs and sub-TLVs" sub-
registry. registry.
Downstream Detailed Mapping TLV (See Section 3.3). Suggested value: Downstream Detailed Mapping TLV (see Section 3.3): 20.
20.
6.2. New Sub-TLV types and associated registry 6.2. New Sub-TLV Types and Associated Registry
IANA is requested to create a new registry for the Sub-Type field of IANA has registered the Sub-Type field of Downstream Detailed Mapping
Downstream Detailed Mapping TLV. The valid range for this is TLV. The valid range for this is 0-65535. Assignments in the range
0-65535. Assignments in the range 0-16383 and 32768-49161 are made 0-16383 and 32768-49161 are made via Standards Action as defined in
via Standards Action as defined in [RFC3692]; assignments in the [RFC3692]; assignments in the range 16384-31743 and 49162-64511 are
range 16384-31743 and 49162-64511 are made via Specification Required made via Specification Required [RFC4379]; values in the range 31744-
([RFC4379]); values in the range 31744-32767 and 64512-65535 are for 32767 and 64512-65535 are for Vendor Private Use, and MUST NOT be
Vendor Private Use, and MUST NOT be allocated. If a sub-TLV has a allocated. If a sub-TLV has a Type that falls in the range for
Type that falls in the range for Vendor Private Use, the Length MUST Vendor Private Use, the Length MUST be at least 4, and the first four
be at least 4, and the first four octets MUST be that vendor's SMI octets MUST be that vendor's SMI Enterprise Code, in network octet
Enterprise Code, in network octet order. The rest of the Value field order. The rest of the Value field is private to the vendor.
is private to the vendor.
It is requested that IANA assign sub-TLV types from this new registry IANA has assigned the following sub-TLV types (see Section 3.3.1):
to the following sub-TLVs (See Section 3.3.1).
Multipath data sub-TLV: Suggested value: 1 Multipath data: 1
Label stack sub-TLV: Suggested value: 2 Label stack: 2
FEC Stack change sub-TLV: Suggested value: 3 FEC stack change: 3
6.3. New Return Codes 6.3. New Return Codes
IANA is requested to assign new Return Code values from the "Multi- IANA has assigned new Return Code values from the "Multi-Protocol
Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
Parameters" registry, "Return Codes" sub-registry as follows using a registry, "Return Codes" sub-registry, as follows using a Standards
Standards Action value. Action value.
Value Meaning Value Meaning
----- ------- ----- -------
TBD See DDM TLV for Return Code and Return SubCode 14 See DDM TLV for Return Code and Return Subcode
TBD Label switched with FEC change 15 Label switched with FEC change
Suggested values: 14 and 15 respectively
7. Acknowledgements 7. Acknowledgements
The authors would like to thank Yakov Rekhter and Adrian Farrel for The authors would like to thank Yakov Rekhter and Adrian Farrel for
their suggestions on the draft. their suggestions on the document.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004. Considered Useful", BCP 82, RFC 3692, January 2004.
skipping to change at page 23, line 5 skipping to change at page 22, line 43
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel, [RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized "Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008. TE)", RFC 5150, February 2008.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream [RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space", Label Assignment and Context-Specific Label Space",
RFC 5331, August 2008. RFC 5331, August 2008.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009.
Authors' Addresses Authors' Addresses
Nitin Bahadur Nitin Bahadur
Juniper Networks, Inc. Juniper Networks, Inc.
1194 N. Mathilda Avenue 1194 N. Mathilda Avenue
Sunnyvale, CA 94089 Sunnyvale, CA 94089
US US
Phone: +1 408 745 2000 Phone: +1 408 745 2000
Email: nitinb@juniper.net EMail: nitinb@juniper.net
URI: www.juniper.net URI: www.juniper.net
Kireeti Kompella Kireeti Kompella
Juniper Networks, Inc. Juniper Networks, Inc.
1194 N. Mathilda Avenue 1194 N. Mathilda Avenue
Sunnyvale, CA 94089 Sunnyvale, CA 94089
US US
Phone: +1 408 745 2000 Phone: +1 408 745 2000
Email: kireeti@juniper.net EMail: kireeti@juniper.net
URI: www.juniper.net URI: www.juniper.net
George Swallow George Swallow
Cisco Systems Cisco Systems
1414 Massachusetts Ave 1414 Massachusetts Ave
Boxborough, MA 01719 Boxborough, MA 01719
US US
Email: swallow@cisco.com EMail: swallow@cisco.com
URI: www.cisco.com URI: www.cisco.com
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