draft-ietf-mpls-lsp-ping-reply-mode-simple-05.txt   rfc7737.txt 
Internet Engineering Task Force N. Akiya Internet Engineering Task Force (IETF) N. Akiya
Internet-Draft Big Switch Networks Request for Comments: 7737 Big Switch Networks
Updates: 7110 (if approved) G. Swallow Updates: 7110 G. Swallow
Intended status: Standards Track C. Pignataro Category: Standards Track C. Pignataro
Expires: April 10, 2016 Cisco Systems ISSN: 2070-1721 Cisco Systems
L. Andersson L. Andersson
M. Chen M. Chen
Huawei Huawei
October 8, 2015 January 2016
Label Switched Path (LSP) Ping/Traceroute Reply Mode Simplification Label Switched Path (LSP) Ping and Traceroute Reply Mode Simplification
draft-ietf-mpls-lsp-ping-reply-mode-simple-05
Abstract Abstract
The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
Ping and Traceroute use the Reply Mode field to signal the method to Ping and Traceroute use the Reply Mode field to signal the method to
be used in the MPLS echo reply. This document updates the procedures be used in the MPLS echo reply. This document updates the procedures
for the "Reply via Specified Path" Reply Mode, the value of this for the "Reply via Specified Path" Reply Mode. The value of this
Reply Mode is 5. The update creates a simple way to indicate that Reply Mode is 5. The update creates a simple way to indicate that
the Reverse LSP should be used as return path. This document also the reverse LSP should be used as the return path. This document
adds an optional TLV which can carry ordered list of Reply Mode also adds an optional TLV that can carry an ordered list of Reply
values. Mode values.
This document updates RFC7110.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", This document updates RFC 7110.
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
Task Force (IETF). Note that other groups may also distribute (IETF). It represents the consensus of the IETF community. It has
working documents as Internet-Drafts. The list of current Internet- received public review and has been approved for publication by the
Drafts is at http://datatracker.ietf.org/drafts/current/. Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference http://www.rfc-editor.org/info/rfc7737.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 10, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statements . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Problem Statements . . . . . . . . . . . . . . . . . . . . . 4
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Reply via Specified Path Update . . . . . . . . . . . . . 5 3.1. "Reply via Specified Path" Reply Mode Update . . . . . . 5
3.2. Reply Mode Order TLV . . . . . . . . . . . . . . . . . . 6 3.2. Reply Mode Order TLV . . . . . . . . . . . . . . . . . . 6
4. Relations to Other LSP Ping/Trace Features . . . . . . . . . 8 4. Relationships to Other LSP Ping and Traceroute Features . . . 8
4.1. Backwards Compatibility with Reply via Specified Path 4.1. Backwards Compatibility with "Reply via Specified Path"
Reply Mode . . . . . . . . . . . . . . . . . . . . . . . 8 Reply Mode . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Reply Path TLV . . . . . . . . . . . . . . . . . . . . . 8 4.2. Reply Path TLV . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Example 1: Reply Mode Order TLV Usage with Reply Path 4.2.1. Example 1: Reply Mode Order TLV Usage with Reply Path
TLV . . . . . . . . . . . . . . . . . . . . . . . . . 9 TLV . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.2. Example 2: Reply Mode Order TLV Usage with Reply Path 4.2.2. Example 2: Reply Mode Order TLV Usage with Reply Path
TLV . . . . . . . . . . . . . . . . . . . . . . . . . 10 TLV . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Proxy LSP Ping . . . . . . . . . . . . . . . . . . . . . 10 4.3. Proxy LSP Ping . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. Proxy LSR Sending an MPLS Echo Request . . . . . . . 10 4.3.1. Proxy LSR Sending an MPLS Echo Request . . . . . . . 10
4.3.2. Proxy LSR Sending an MPLS Proxy Ping Reply . . . . . 11 4.3.2. Proxy LSR Sending an MPLS Proxy Ping Reply . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Manageability Considerations . . . . . . . . . . . . . . . . 11 6. Manageability Considerations . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7.1. New Reply Mode Order TLV . . . . . . . . . . . . . . . . 12 7.1. New Reply Mode Order TLV . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 13 Appendix A. Reply Mode Order TLV Beneficial Scenarios . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Reply Mode Order TLV Beneficial Scenarios . . . . . 13
A.1. Incorrect Forwarding Scenario . . . . . . . . . . . . . . 14 A.1. Incorrect Forwarding Scenario . . . . . . . . . . . . . . 14
A.2. Non-Co-Routed Bidirectional LSP Scenario . . . . . . . . 14 A.2. Non-Co-Routed Bidirectional LSP Scenario . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Ping,
Ping, described in [RFC4379], allows an initiator LSR to encode as described in [RFC4379], allows an initiator Label Switching Router
instructions (Reply Mode) on how a responder LSR should send the (LSR) to encode instructions (Reply Mode) on how a responder LSR
response back to the initiator LSR. [RFC7110] also allows the should send the response back to the initiator LSR. [RFC7110] also
initiator LSR to encode a TLV (Reply Path TLV) which can instruct the allows the initiator LSR to encode a TLV (Reply Path TLV) that can
responder LSR to use a specific LSP to send the response back to the instruct the responder LSR to use a specific LSP to send the response
initiator LSR. Both approaches are powerful as they provide the back to the initiator LSR. Both approaches are powerful, as they
ability for the initiator LSR to control the return path. provide the ability for the initiator LSR to control the return path.
However, it is becoming increasingly difficult for an initiator LSR However, it is becoming increasingly difficult for an initiator LSR
to select a valid return path to encode in the MPLS LSP echo request to select a valid return path to encode in the MPLS LSP echo request
packets. If the initiator LSR does not select a valid return path, packets. If the initiator LSR does not select a valid return path,
the MPLS LSP echo reply will not get back to the initiator LSR. This the MPLS LSP echo reply will not get back to the initiator LSR. This
results in a false failure of MPLS LSP Ping and Traceroute operation. results in a false failure of MPLS LSP Ping and Traceroute
In an effort to minimize such false failures, different operations. In an effort to minimize such false failures, different
implementations have chosen different default return path encoding implementations have chosen different default return path encoding
for different LSP types and LSP operations. The problem with for different LSP types and LSP operations. The problem with
implementations having different default return path encoding is that implementations having different default return path encoding is that
the MPLS echo reply will not work in many cases, and the default the MPLS echo reply will not work in many cases, and the default
value may not be the preferred choice by the operators. value may not be the preferred choice of the operators.
This document describes: This document describes the following:
o In Section 2, further description of the problems; o In Section 2, further description of the problems;
o In Section 3, a solution to minimize false failures while o In Section 3, a solution to minimize false failures while
accommodating operator preferences; accommodating operator preferences;
o In Section 4, relationships to other LSP Ping/Traceroute features; o In Section 4, relationships to other LSP Ping and Traceroute
features;
o In Appendix A, examples of scenarios where the mechanism described o In Appendix A, examples of scenarios where the mechanism described
in this document provides benefits. in this document provides benefits.
This document updates [RFC7110] by allowing the usage of the "Reply This document updates [RFC7110] by allowing the usage of the "Reply
via Specified Path" (value=5) Reply Mode without including the Reply via Specified Path" (value=5) Reply Mode without including the Reply
Path TLV. The update creates a simple way to indicate that the Path TLV. The update creates a simple way to indicate that the
Reverse LSP should be used as return path. reverse LSP should be used as the return path.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Problem Statements 2. Problem Statements
It is becoming increasingly difficult for implementations to It is becoming increasingly difficult for implementations to
automatically supply a workable return path encoding for all MPLS LSP automatically supply a workable return path encoding for all MPLS LSP
Ping and Traceroute operations across all LSP types. There are Ping and Traceroute operations across all LSP types. There are
several factors which are contributing to this complication. several factors that contribute to this complication.
o Some LSPs have a control-channel, and some do not. Some LSPs have o Some LSPs have a control channel, and some do not. Some LSPs have
a reverse LSP, and some do not. Some LSPs have IP reachability in a reverse LSP, and some do not. Some LSPs have IP reachability in
the reverse direction, and some do not. the reverse direction, and some do not.
o LSRs on some LSPs can have different available return path(s). o LSRs on some LSPs can have different available return path(s).
Available return path(s) can depend on whether the responder LSR Available return path(s) can depend on whether the responder LSR
is a transit LSR or an egress LSR. In case of a bi-directional is a transit LSR or an egress LSR. In the case of a bidirectional
LSP, available return path(s) on transit LSRs can also depend on LSP, available return path(s) on transit LSRs can also depend on
whether the LSP is completely co-routed, partially co-routed or whether the LSP is completely co-routed, partially co-routed, or
associated (i.e., the LSPs in the two directions are not co- associated (i.e., the LSPs in the two directions are not
routed). co-routed).
o MPLS echo request packets may incorrectly terminate on an o MPLS echo request packets may incorrectly terminate on an
unintended target, which can have different available return unintended target that can have different available return path(s)
path(s) than the intended target. than the intended target.
o The MPLS LSP Ping operation is expected to terminate on an egress o The MPLS LSP Ping operation is expected to terminate on an egress
LSR. However, the MPLS LSP Ping operation with specific TTL LSR. However, MPLS LSP Ping operations with specific TTL values
values and MPLS LSP Traceroute operation can terminate on both and MPLS LSP Traceroute operations can terminate on both transit
transit LSR(s) and the egress LSR. LSR(s) and the egress LSR.
Except for the case where the responder LSR does not have an IP route Except for the case where the responder LSR does not have an IP route
back to the initiator LSR, it is possible to use the "Reply via an back to the initiator LSR, it is possible to use the "Reply via an
IPv4/IPv6 UDP packet" (value=2) Reply Mode value in all cases. IPv4/IPv6 UDP packet" (value=2) Reply Mode value in all cases.
However, some operators are preferring control-channel and reverse However, some operators prefer the control channel and a reverse LSP
LSP as default return path if they are available, which is not always as the default return path if they are both available, although this
the case. is not always the case.
When specific return path encoding is supplied by users or When specific return path encoding is supplied by users or
applications, then there are no issues in choosing the return path applications, then there are no issues in choosing the return path
encoding. When specific return path encoding is not supplied by encoding. When specific return path encoding is not supplied by
users or applications, then implementations use extra logic to users or applications, then implementations use extra logic to
compute, and sometimes guess, the default return path encodings. If compute, and sometimes guess, the default return path encodings. If
a responder LSR receives an MPLS echo request containing return path a responder LSR receives an MPLS echo request containing return path
instructions which cannot be accommodated due to unavailability, then instructions that cannot be accommodated due to unavailability, then
the responder LSR often drops such packets. This failure mode the responder LSR often drops such packets. This failure mode
results in the initiator LSR not receiving the intended MPLS LSP echo results in the initiator LSR not receiving the intended MPLS LSP echo
reply packets. The scenario described here is a potentially reply packets. The scenario described here is a potentially
acceptable result in some failure cases, like a broken LSP, where the acceptable result in some failure cases, like a broken LSP, where the
MPLS echo request terminated on an unintended target. However, if MPLS echo request terminated on an unintended target. However, if
the initiator LSR does not receive an MPLS echo replay, even after the initiator LSR does not receive an MPLS echo reply even after the
the responder LSR receives the MPLS echo request and is able to responder LSR receives the MPLS echo request and is able to verify
verify the request, information is sent back to the user(s) which is the request, information is still sent back to the user(s); this is
considered a false failure. considered a false failure.
Many operators prefer particular return path(s) over others return Many operators prefer particular return path(s) over other return
path(s) for specific LSP types. To accommodate operator preferred path(s) for specific LSP types. To accommodate operator-preferred
paths, implementations may default to operator preferred return paths paths, implementations may default to operator-preferred return paths
for particular operations, or allow a default return path to be for particular operations or allow a default return path to be
configured. It would not be considered beneficial to use a preferred configured. It would not be considered beneficial to use a preferred
return path for an intended target LSR if there is previous knowledge return path for an intended target LSR if there is previous knowledge
at the initiator LSR that the return path is not available. Using a at the initiator LSR that the return path is not available. Using an
unavailable preferred return path would undesirably result in the unavailable preferred return path would undesirably result in the
initiator LSR not receiving the MPLS echo return packets. It would initiator LSR not receiving the MPLS echo return packets. It would
be considered beneficial, for given operations, if the sender of the be considered beneficial, for given operations, if the sender of the
MPLS echo request would be able to determined return path MPLS echo request would be able to determine return path availability
availability before the operation is initiated. before the operation is initiated.
This document updates the procedures for "Reply via Specified Path" This document (1) updates the procedures for the "Reply via Specified
Reply Mode to easily indicate the reverse LSP, and adds one optional Path" Reply Mode to easily indicate the reverse LSP and (2) adds one
TLV to describe an ordered list of Reply Modes. Based on operational optional TLV to describe an ordered list of Reply Modes. Based on
needs, the TLV can describe multiple Reply Mode values in a preferred operational needs, the TLV can list multiple Reply Mode values in a
order to allow the responder LSR to use the first available Reply preferred order to allow the responder LSR to use the first available
Mode from the list. This eliminates the need for the initiator LSR Reply Mode from the list. This eliminates the need for the initiator
to compute, or sometimes guess, the default return path encoding. LSR to compute, or sometimes guess, the default return path encoding.
This new mode of operation would resulted in a simplification to This new mode of operation would result in simplified implementations
implementations across the various vendors and improve both usability across the various vendors and improve both usability and operational
and operational needs. needs.
3. Solution 3. Solution
This document updates the procedures for "Reply via Specified Path" This document updates the procedures for the "Reply via Specified
Reply Mode to easily indicate the reverse LSP. This document also Path" Reply Mode to easily indicate the reverse LSP. This document
adds an optional TLV which can carry an ordered list of Reply Modes. also adds an optional TLV that can carry an ordered list of Reply
Modes.
3.1. Reply via Specified Path Update 3.1. "Reply via Specified Path" Reply Mode Update
Some LSP types are capable of having a related LSP in reverse Some LSP types are capable of having a related LSP in the reverse
direction, through signaling or other association mechanisms. direction, through signaling or other association mechanisms.
Examples of such LSP types are bidirectional Resource ReserVation Examples of such LSP types are bidirectional Resource Reservation
Protocol-Traffic Engineering (RSVP-TE) LSPs [RFC3473] and MPLS Protocol-Traffic Engineering (RSVP-TE) LSPs [RFC3473] and MPLS
Transport Profile (MPLS-TP) LSPs ([RFC5960]). This document uses the Transport Profile (MPLS-TP) LSPs [RFC5960]. This document uses the
term "Reverse LSP" to refer to the LSP in the reverse direction of term "reverse LSP" to refer to the LSP in the reverse direction of
such LSP types. Note that this document restricts the scope of such LSP types. Note that this document restricts the scope of
"Reverse LSP" applicability to those reverse LSPs which are capable "reverse LSP" applicability to those reverse LSPs that are capable
and allowed to carry the IP encapsulated MPLS echo reply. and allowed to carry the IP encapsulated MPLS echo reply.
[RFC7110] has defined the Reply Mode "Reply via Specified Path" which [RFC7110] has defined the Reply Mode "Reply via Specified Path",
allows the initiator LSR to instruct the responder LSR to send the which allows the initiator LSR to instruct the responder LSR to send
MPLS echo reply message on the reverse LSP. However, the instruction the MPLS echo reply message on the reverse LSP. However, the
also requires the initiator LSR to include the "Reply Path TLV" with instruction also requires the initiator LSR to include the Reply Path
the B bit (Bidirectional bit) set in the Flags field. Additionally, TLV with the B bit (Bidirectional bit) set in the Flags field.
[RFC7110] defines that if the "Reply via Specified Path" Reply Mode Additionally, [RFC7110] specifies that if the "Reply via Specified
is used the "Reply Path TLV" MUST present. Path" Reply Mode is used the Reply Path TLV MUST be present.
This document updates the procedures for "Reply via Specified Path" This document updates the procedures for the "Reply via Specified
Reply Mode as follows: Path" Reply Mode as follows:
o The "Reply via Specified Path" MAY be used without including a o The "Reply via Specified Path" Reply Mode MAY be used without
"Reply Path TLV". including a Reply Path TLV.
o The usage of the "Reply via Specified Path" without inclusion of a o The usage of the "Reply via Specified Path" Reply Mode without the
"Reply Path TLV" implies the reverse LSP. In other words, the inclusion of a Reply Path TLV implies the reverse LSP. In other
usage of the "Reply via Specified Path" without inclusion of a words, the usage of the "Reply via Specified Path" Reply Mode
"Reply Path TLV" has the same semantics as the usage of the "Reply without the inclusion of a Reply Path TLV has the same semantics
via Specified Path" with inclusion of a "Reply Path TLV" with the as the usage of the "Reply via Specified Path" Reply Mode with the
B bit set in the Flags field. inclusion of a Reply Path TLV with the B bit set in the Flags
field.
Specific to section 5.1 of [RFC7110], this document updates the first This document updates the first sentence of Section 5.1 of [RFC7110]
sentence as follows: as follows:
o When sending an echo request, in addition to the rules and o When sending an echo request, in addition to the rules and
procedures defined in Section 4.3 of [RFC4379], the Reply Mode of procedures defined in Section 4.3 of [RFC4379], the Reply Mode of
the echo request MUST be set to "Reply via Specified Path", and a the echo request MUST be set to "Reply via Specified Path", and a
Reply Path TLV SHOULD be carried in the echo request message Reply Path TLV SHOULD be carried in the echo request message
correspondingly; if the Reply Path TLV is not carried, then it correspondingly; if the Reply Path TLV is not carried in the
indicates the reverse LSP as the reply path. message, then it indicates the reverse LSP as the reply path.
Note that the reverse LSP is in relation to the last FEC specified in Note that the reverse LSP is in relation to the last Forwarding
the Target FEC Stack TLV. Equivalence Class (FEC) specified in the Target FEC Stack TLV.
3.2. Reply Mode Order TLV 3.2. Reply Mode Order TLV
This document also introduces a new optional TLV to describe a list This document also introduces a new optional TLV to describe a list
of Reply Mode values. The new TLV will contain one or more Reply of Reply Mode values. The new TLV will contain one or more Reply
Mode value(s) in preferred order. The first Reply Mode value is the Mode values in preferred order. The first Reply Mode value is the
most preferred and the last Reply Mode value is the least preferred. most preferred, and the last Reply Mode value is the least preferred.
Following rules apply when using Reply Mode Order TLV. The following rules apply when using the Reply Mode Order TLV:
1. The Reply Mode Order TLV MUST NOT be included in any MPLS echo 1. The Reply Mode Order TLV MUST NOT be included in any MPLS echo
reply. If the initiator LSR receives an MPLS echo reply with the reply. If the initiator LSR receives an MPLS echo reply with the
Reply Mode Order TLV, the initiator LSR MUST ignore the whole Reply Mode Order TLV, the initiator LSR MUST ignore the whole
Reply Mode Order TLV and MUST only use the value from the Reply Reply Mode Order TLV and MUST only use the value from the Reply
Mode field of the received MPLS echo reply. It may be beneficial Mode field of the received MPLS echo reply. It may be beneficial
for implementations to provide counters and/or loggings, with for implementations to provide counters and/or logs, with
appropriate log dampening, to record this error case. appropriate log dampening, to record this error case.
2. The Reply Mode Order TLV MAY be included in MPLS echo request. 2. The Reply Mode Order TLV MAY be included in MPLS echo requests.
3. The Reply Mode field of an MPLS echo request MUST be set to a 3. The Reply Mode field of an MPLS echo request MUST be set to a
valid value even when supplying the Reply Mode Order TLV. The valid value even when supplying the Reply Mode Order TLV. The
initiator LSR SHOULD set the Reply Mode field of an MPLS echo initiator LSR SHOULD set the Reply Mode field of an MPLS echo
request to a value that corresponds to a return path which most request to a value that corresponds to a return path that is most
likely to be available, in case the responder LSR does not likely to be available, in case the responder LSR does not
understand the Reply Mode Order TLV. understand the Reply Mode Order TLV.
4. If a responder LSR understands the Reply Mode Order TLV but the 4. If a responder LSR understands the Reply Mode Order TLV but the
TLV is not valid (due to conditions described in the items 6, 7, TLV is not valid (due to the conditions described in items 6, 7,
8 and 9 immediately below), then the responder LSR MUST ignore 8, and 9 below), then the responder LSR MUST ignore the whole
the whole Reply Mode Order TLV and MUST only use the value from Reply Mode Order TLV and MUST only use the value from the Reply
the Reply Mode field of the received MPLS echo request. It may Mode field of the received MPLS echo request. It may be
be beneficial for implementations to provide counters and/or beneficial for implementations to provide counters and/or logs,
loggings, with appropriate log dampening, to record this error with appropriate log dampening, to record this error case.
case.
5. If a responder LSR understands the Reply Mode Order TLV and the 5. If a responder LSR understands the Reply Mode Order TLV and the
TLV is valid, then the responder LSR MUST consider the Reply Mode TLV is valid, then the responder LSR MUST consider the Reply Mode
values described in the TLV and MUST NOT use the value described values specified in the TLV and MUST NOT use the value specified
in the Reply Mode field of the received MPLS echo request. In in the Reply Mode field of the received MPLS echo request. In
other words, a valid Reply Mode Order TLV overrides the value other words, a valid Reply Mode Order TLV overrides the value
specified in the Reply Mode field of the received MPLS echo specified in the Reply Mode field of the received MPLS echo
request. request.
6. Reply Mode Order TLV MUST contain at least one Reply Mode value. 6. The Reply Mode Order TLV MUST contain at least one Reply Mode
value.
7. A Reply Mode value, except for Reply Mode value 5 (Reply via 7. A Reply Mode value, except for Reply Mode value 5 (Reply via
Specified Path), MUST NOT be repeated (i.e., MUST NOT appear Specified Path), MUST NOT be repeated (i.e., MUST NOT appear
multiple times) in the Reply Mode Order TLV. multiple times) in the Reply Mode Order TLV.
8. The Reply Mode value 5 (Reply via Specified Path) MAY be included 8. Reply Mode value 5 (Reply via Specified Path) MAY be included
more than once in the Reply Mode Order TLV. However, in such more than once in the Reply Mode Order TLV. However, in such a
case a Reply Path TLV MUST be included for all instances of the case, a Reply Path TLV MUST be included for all instances of
Reply Mode value 5 included in the Reply Mode Order TLV. In Reply Mode value 5 that are included in the Reply Mode Order TLV.
other words, 3 instances of the Reply Mode value 5 in the Reply In other words, three instances of Reply Mode value 5 in the
Mode Order TLV will require 3 instances of the Reply Path TLVs. Reply Mode Order TLV will each require a Reply Path TLV.
9. The Reply Mode value 1 (Do not reply) MUST NOT be used in the 9. The Reply Mode value 1 (Do not reply) MUST NOT be used in the
Reply Mode Order TLV. Reply Mode Order TLV.
The responder LSR SHOULD select the first available return path in The responder LSR SHOULD select the first available return path in
this TLV. The Reply Mode value corresponding to the selected return this TLV. The Reply Mode value corresponding to the selected return
path MUST be set in Reply Mode field of the MPLS echo reply to path MUST be set in the Reply Mode field of the MPLS echo reply to
communicate back to the initiator LSR which return path was chosen. communicate back to the initiator LSR which return path was chosen.
The format of the TLV is as follows: The format of the TLV is as follows:
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Mode Order TLV Type | Length | | Reply Mode Order TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Reply Mode 1 | Reply Mode 2 | Reply Mode 3 | Reply Mode 4 ~ ~ Reply Mode 1 | Reply Mode 2 | Reply Mode 3 | Reply Mode 4 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Reply Mode Order TLV
This is a variable length optional TLV. The Reply Mode Order TLV Figure 1: Reply Mode Order TLV
Type is TBD1.
The Length field is 2 octets in length. It defines the length in This is a variable-length optional TLV. The Reply Mode Order TLV
octets of the list of Reply Mode values. Type is 32770.
The Length field is 2 octets in length. It defines the length, in
octets, of the list of Reply Mode values.
Each Reply Mode field is 1 octet, and there is no padding. Each Reply Mode field is 1 octet, and there is no padding.
4. Relations to Other LSP Ping/Trace Features 4. Relationships to Other LSP Ping and Traceroute Features
4.1. Backwards Compatibility with Reply via Specified Path Reply Mode 4.1. Backwards Compatibility with "Reply via Specified Path" Reply Mode
[RFC7110] introduces the "Reply via Specified Path" (value=5) Reply [RFC7110] introduces the "Reply via Specified Path" (value=5) Reply
Mode. The RFC also defines that if this Reply Mode is used, the Mode. [RFC7110] also specifies that if this Reply Mode is used the
"Reply Path TLV" MUST be included. This document relaxes the Reply Path TLV MUST be included. This document relaxes the semantics
semantics and defines that this Reply Mode MAY be used without the and specifies that this Reply Mode MAY be used without the Reply Path
"Reply Path TLV". This MAY be done to indicate that the reverse LSP TLV. This MAY be done to indicate that the reverse LSP SHALL be used
SHALL be used as he return path. as the return path.
If the initiator LSR, which sent an MPLS echo request message with If an initiator LSR that sent an MPLS echo request message with the
the "Reply via Specified Path" Reply Mode but without including the "Reply via Specified Path" Reply Mode but without including the Reply
"Reply Path TLV", receives back an MPLS echo reply message with the Path TLV receives back an MPLS echo reply message with a return code
return code being "Malformed echo request received", then the of "Malformed echo request received", then the initiator LSR SHOULD
initiator LSR SHOULD assume that the responder LSR does not support assume that the responder LSR does not support the mechanism defined
the mechanism defined in this document. in this document.
4.2. Reply Path TLV 4.2. Reply Path TLV
A "Reply Path TLV" [RFC7110] is defined to identify a single return A Reply Path TLV [RFC7110] is defined to identify a single return
path. When the initiator LSR wants to use the Reply Mode Order TLV path. When the initiator LSR wants to use the Reply Mode Order TLV
to describe multiple return paths, then the initiator SHOULD include to specify multiple return paths, then the initiator LSR SHOULD
multiple "Reply via Specified Path" (value=5) Reply Mode values and include multiple "Reply via Specified Path" (value=5) Reply Mode
multiple corresponding "Reply Path TLV" objects (one "Reply Path TLV" values and multiple corresponding Reply Path TLV objects (one Reply
corresponding to a "Reply via Specified Path" Reply Mode, and one Path TLV corresponding to a "Reply via Specified Path" Reply Mode and
"Reply Path TLV" identifies a return path). one Reply Path TLV identifying a return path).
As described in Section 3.1, it's valid to use the "Reply via As described in Section 3.1, it is valid to use the "Reply via
Specified Path" Reply Mode without inclusion a "Reply Path TLV". For Specified Path" Reply Mode without inclusion in a Reply Path TLV.
the Reply Mode Order TLV, it's also valid to include a "Reply via For the Reply Mode Order TLV, it is also valid to include a "Reply
Specified Path" Reply Mode value without a corresponding "Reply Path via Specified Path" Reply Mode value without a corresponding Reply
TLV", this implies that the reverse LSP is the preferred return path. Path TLV; this implies that the reverse LSP is the preferred return
When multiple consecutive "Reply via Specified Path" Reply Mode path. When multiple consecutive "Reply via Specified Path" Reply
values are included but less corresponding "Reply Path TLV" objects Mode values are included but fewer corresponding Reply Path TLV
exist, the responder LSR SHOULD think that the former "Reply via objects exist, the responder LSR SHOULD think that the former "Reply
Specified Path" Reply Mode values have corresponding "Reply Path via Specified Path" Reply Mode values have corresponding Reply Path
TLV", the latter "Reply via Specified Path" Reply Mode values have no TLVs. The latter "Reply via Specified Path" Reply Mode values have
corresponding "Reply Path TLV". For example, if the Reply Mode Order no corresponding Reply Path TLVs. For example, if the Reply Mode
TLV carrying Reply Modes {5, 5, 5} and only two Reply Path TLVs Order TLV carries Reply Modes {5, 5, 5} and only two Reply Path TLVs
carrying FEC X and FEC Y respectively. The reply path order is as carry FEC X and FEC Y, respectively, then the reply path order is as
follows: follows:
1. Reply via Specified Path (FEC X) 1. Reply via Specified Path (FEC X)
2. Reply via Specified Path (FEC Y) 2. Reply via Specified Path (FEC Y)
3. Reply via Specified Path (Reverse LSP) 3. Reply via Specified Path (reverse LSP)
4.2.1. Example 1: Reply Mode Order TLV Usage with Reply Path TLV 4.2.1. Example 1: Reply Mode Order TLV Usage with Reply Path TLV
If the initiator LSR was interested in encoding following return If the initiator LSR was interested in encoding the following return
paths: paths:
1. Reply via application level control channel 1. Reply via application level control channel
2. FEC X 2. FEC X
3. FEC Y 3. FEC Y
4. Reply via an IPv4/IPv6 UDP packet 4. Reply via an IPv4/IPv6 UDP packet
Then the MPLS echo request message is to carry: Then the MPLS echo request message is to carry:
o The Reply Mode Order TLV carrying Reply Modes {4, 5, 5, 2} o The Reply Mode Order TLV carrying Reply Modes {4, 5, 5, 2}
o One Reply Path TLV carrying FEC X o One Reply Path TLV carrying FEC X
o One Reply Path TLV carrying FEC Y o One Reply Path TLV carrying FEC Y
The encoding specified by the Reply Mode Order TLV and the Reply Path
Described encoding of the Reply Mode Order TLV and the Reply Path TLV TLV in the MPLS echo request message will cause the responder LSR to
in the MPLS echo request message will result in the responder LSR to
prefer "Reply via application level control channel (4)", followed by prefer "Reply via application level control channel (4)", followed by
FEC X, FEC Y and then "Reply via an IPv4/IPv6 UDP packet (2)". FEC X, FEC Y, and then "Reply via an IPv4/IPv6 UDP packet (2)".
4.2.2. Example 2: Reply Mode Order TLV Usage with Reply Path TLV 4.2.2. Example 2: Reply Mode Order TLV Usage with Reply Path TLV
If the initiator LSR was interested in encoding following return If the initiator LSR was interested in encoding the following return
paths: paths:
1. Reverse LSP 1. Reverse LSP
2. Reply via an IPv4/IPv6 UDP packet 2. Reply via an IPv4/IPv6 UDP packet
3. FEC X 3. FEC X
4. FEC Y 4. FEC Y
Then the MPLS echo request message is to carry: Then the MPLS echo request message is to carry:
o The Reply Mode Order TLV carrying Reply Modes {5, 2, 5, 5} o The Reply Mode Order TLV carrying Reply Modes {5, 2, 5, 5}
o One Reply Path TLV with the B bit set. o One Reply Path TLV with the B bit set
o One Reply Path TLV carrying FEC X o One Reply Path TLV carrying FEC X
o One Reply Path TLV carrying FEC Y o One Reply Path TLV carrying FEC Y
Described encoding of the Reply Mode Order TLV and the Reply Path TLV The encoding specified by the Reply Mode Order TLV and the Reply Path
in the MPLS echo request message will result in the responder LSR to TLV in the MPLS echo request message will cause the responder LSR to
prefer the reverse LSP, followed by "Reply via an IPv4/IPv6 UDP prefer the reverse LSP, followed by "Reply via an IPv4/IPv6 UDP
packet (2)", FEC X and then FEC Y. packet (2)", FEC X, and then FEC Y.
4.3. Proxy LSP Ping 4.3. Proxy LSP Ping
The mechanism defined in this document will work with Proxy LSP Ping The mechanism defined in this document will work with Proxy LSP Ping
defined by [RFC7555]. The MPLS proxy ping request message can carry as defined by [RFC7555]. The MPLS proxy ping request message can
a Reply Mode value in the header and one or more Reply Mode values in carry a Reply Mode value in the header and one or more Reply Mode
the Reply Mode Order TLV. It is RECOMMENDED that the Reply Mode 2 values in the Reply Mode Order TLV. It is RECOMMENDED that Reply
(Reply via an IPv4/IPv6 UDP packet) be used in the Reply Mode field Mode 2 (Reply via an IPv4/IPv6 UDP packet) be used in the Reply Mode
of the MPLS proxy ping request message. field of the MPLS proxy ping request message.
4.3.1. Proxy LSR Sending an MPLS Echo Request 4.3.1. Proxy LSR Sending an MPLS Echo Request
If the proxy LSR is sending an MPLS echo request, then the proxy LSR If the proxy LSR is sending an MPLS echo request, then the proxy LSR
MUST copy the following elements from the MPLS proxy ping request MUST copy the following elements from the MPLS proxy ping request
message to the MPLS echo request message. message to the MPLS echo request message:
o The Reply Mode field. o The Reply Mode field.
o The Reply Mode Order TLV. o The Reply Mode Order TLV.
o The Reply Path TLV(s). If there are more than one Reply Path o The Reply Path TLV(s). If there is more than one Reply Path TLV,
TLVs, then order of them MUST be preserved when copying. then the ordering of the TLVs MUST be preserved when copying.
4.3.2. Proxy LSR Sending an MPLS Proxy Ping Reply 4.3.2. Proxy LSR Sending an MPLS Proxy Ping Reply
If the proxy LSR is sending an MPLS proxy ping reply, then it is If the proxy LSR is sending an MPLS proxy ping reply, then it is
RECOMMENDED that the Reply Mode Order TLV is ignored and the Reply RECOMMENDED that the Reply Mode Order TLV be ignored and the Reply
Mode field in the MPLS proxy ping request message is used. Mode field in the MPLS proxy ping request message be used.
5. Security Considerations 5. Security Considerations
Those security considerations specified in [RFC4379] and [RFC7110] The security considerations specified in [RFC4379] and [RFC7110] also
apply for this document. apply for this document.
In addition, this document introduces the Reply Mode Order TLV. It In addition, this document introduces the Reply Mode Order TLV. It
provides a new way for an unauthorized source to gather more network provides a new way for an unauthorized source to gather more network
information, especially the potential return path(s) information of information, especially information regarding the potential return
an LSP. To protect against unauthorized sources using MPLS echo path(s) of an LSP. To protect against unauthorized sources using
request messages with the Reply Mode Order TLV to obtain network MPLS echo request messages with the Reply Mode Order TLV to obtain
information, similar to [RFC4379], it is RECOMMENDED that network information, as also specified in [RFC4379], it is
implementations provide a means of checking the source addresses of RECOMMENDED that implementations provide a means of checking the
MPLS echo request messages against an access list before accepting source addresses of MPLS echo request messages against an access list
the message. before accepting the message.
Another potential security issue is that the MPLS echo request and Another potential security issue is that the MPLS echo request and
reply messages are not encrypted, the content of the MPLS echo reply messages are not encrypted; the contents of the MPLS echo
request and reply messages may be potentially exposed. Although the request and reply messages may therefore be potentially exposed.
exposure is within the MPLS domain, if such exposure is a concern, Although the exposure is within the MPLS domain, if such exposure is
some encryption mechanisms [I-D.ietf-mpls-opportunistic-encrypt] may a concern, some encryption mechanisms [MPLS-OPP-ENCR] may be
be employed. employed.
6. Manageability Considerations 6. Manageability Considerations
Section 2 described the problems which increases the complexity with Section 2 described problems that increase complexity with respect to
respect to operations and implementations. In order to simplify operations and implementations. In order to simplify operations and
operations and to allow for the LSP Ping/Traceroute to function to allow LSP Ping and Traceroute to function efficiently whilst
efficiently whilst preserving the code simplicity, it is RECOMMENDED preserving code simplicity, it is RECOMMENDED that implementations
that implementations allow devices to have configuration options to allow devices to have configuration options to set operator-preferred
set operator preferred Reply Modes. For example: Reply Modes. For example:
o For those operators who are more interested in MPLS echo reply o For those operators who are more interested in MPLS echo reply
packets reaching back to the initiator LSR: packets reaching the initiator LSR:
1. Reply via an IPv4/IPv6 UDP packet (2) 1. Reply via an IPv4/IPv6 UDP packet (2)
2. Reply via application level control channel (4) 2. Reply via application level control channel (4)
3. Reply via Specified Path (5) 3. Reply via Specified Path (5)
o For those operators who are more interested in MPLS echo reply o For those operators who are more interested in MPLS echo reply
packets testing the paths related to the forward LSP: packets testing the paths related to the forward LSP:
1. Reply via Specified Path (5) 1. Reply via Specified Path (5)
2. Reply via application level control channel (4) 2. Reply via application level control channel (4)
skipping to change at page 12, line 18 skipping to change at page 12, line 21
1. Reply via Specified Path (5) 1. Reply via Specified Path (5)
2. Reply via application level control channel (4) 2. Reply via application level control channel (4)
3. Reply via an IPv4/IPv6 UDP packet (2) 3. Reply via an IPv4/IPv6 UDP packet (2)
7. IANA Considerations 7. IANA Considerations
7.1. New Reply Mode Order TLV 7.1. New Reply Mode Order TLV
IANA is requested to assign a new TLV type value from the "TLVs" sub- IANA has assigned a new TLV type value from the "TLVs" sub-registry
registry within the "Multiprotocol Label Switching Architecture within the "Multiprotocol Label Switching Architecture (MPLS) Label
(MPLS)" registry, for the "Reply Mode Order TLV". Switched Paths (LSPs) Ping Parameters" registry, for the Reply Mode
Order TLV.
The new TLV Type value should be assigned from the range
(32768-49161) specified in [RFC4379] section 3 that allows the TLV
type to be silently dropped if not recognized.
Type Meaning Reference
---- ------- ---------
TBD1 Reply Mode Order TLV this document
8. Acknowledgements
Authors would like to thank Santiago Alvarez and Faisal Iqbal for The new TLV Type value has been assigned from the range 32768-49161,
discussions which motivated creation of this document. Authors would as specified in Sections 3 and 7.2 of [RFC4379]; this range is for
also like to thank Sam Aldrin, Curtis Villamizar, Ross Callon, optional TLVs that can be silently dropped if not recognized.
Jeffrey Zhang, Jeremy Whittaker, Mustapha Alissaoui, Qin Wu, Jie Dong
and Adrian Farrel for providing valuable comments to influence the
contents of the draft. Authors would also like to thank Dan Frost,
Tom Taylor, Victor Kuarsingh and Deborah Brungard for reviewing the
document and providing useful comments.
9. Contributing Authors Type Meaning Reference
----- ------- ---------
32770 Reply Mode Order TLV RFC 7737
Shaleen Saxena 8. References
Brocade
Email: ssaxena@brocade.com
10. References 8.1. Normative References
10.1. 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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379, Label Switched (MPLS) Data Plane Failures", RFC 4379,
DOI 10.17487/RFC4379, February 2006, DOI 10.17487/RFC4379, February 2006,
<http://www.rfc-editor.org/info/rfc4379>. <http://www.rfc-editor.org/info/rfc4379>.
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping", "Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014, RFC 7110, DOI 10.17487/RFC7110, January 2014,
<http://www.rfc-editor.org/info/rfc7110>. <http://www.rfc-editor.org/info/rfc7110>.
10.2. Informative References 8.2. Informative References
[I-D.ietf-mpls-opportunistic-encrypt] [MPLS-OPP-ENCR]
Farrel, A. and S. Farrell, "Opportunistic Security in MPLS Farrel, A. and S. Farrell, "Opportunistic Security in MPLS
Networks", draft-ietf-mpls-opportunistic-encrypt-00 (work Networks", Work in Progress, draft-ietf-mpls-
in progress), July 2015. opportunistic-encrypt-00, July 2015.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol- Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473, Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003, DOI 10.17487/RFC3473, January 2003,
<http://www.rfc-editor.org/info/rfc3473>. <http://www.rfc-editor.org/info/rfc3473>.
[RFC5960] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS [RFC5960] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS
Transport Profile Data Plane Architecture", RFC 5960, Transport Profile Data Plane Architecture", RFC 5960,
DOI 10.17487/RFC5960, August 2010, DOI 10.17487/RFC5960, August 2010,
<http://www.rfc-editor.org/info/rfc5960>. <http://www.rfc-editor.org/info/rfc5960>.
[RFC7555] Swallow, G., Lim, V., and S. Aldrin, "Proxy MPLS Echo [RFC7555] Swallow, G., Lim, V., and S. Aldrin, "Proxy MPLS Echo
Request", RFC 7555, DOI 10.17487/RFC7555, June 2015, Request", RFC 7555, DOI 10.17487/RFC7555, June 2015,
<http://www.rfc-editor.org/info/rfc7555>. <http://www.rfc-editor.org/info/rfc7555>.
Appendix A. Reply Mode Order TLV Beneficial Scenarios Appendix A. Reply Mode Order TLV Beneficial Scenarios
This section lists examples of how the Reply Mode Order TLV can This section lists examples of how the Reply Mode Order TLV can be
benefit. beneficial.
A.1. Incorrect Forwarding Scenario A.1. Incorrect Forwarding Scenario
As shown in Figure 2, a network has an LSP with the forwarding path: As shown in Figure 2, a network has an LSP with the forwarding path
A-B-C-D-E. The LSP has a control channel. A-B-C-D-E. The LSP has a control channel.
A------B------C------D------E A------B------C------D------E
| |
| |
F F
Forward Paths: A-B-C-D-E Forward Path: A-B-C-D-E
Figure 2: Incorrect Forwarding Figure 2: Incorrect Forwarding
If D is incorrectly label switching to F (instead of E). In this If D is incorrectly label switching to F (instead of E), then LSP
scenario, LSP Traceroute with "Reply via application level control Traceroute with "Reply via application level control channel (4)"
channel (4)" will result in following result. will result in the following:
Success (Reply from B) Success (Reply from B)
Success (Reply from C) Success (Reply from C)
Success (Reply from D) Success (Reply from D)
Timeout... Timeout...
Complete Complete
This is because F does not have a control channel to send the MPLS This is because F does not have a control channel on which to send
echo reply message. With the extension described in this document, the MPLS echo reply message. With the extensions described in this
same procedures can be performed with the Reply Mode Order TLV document, the same procedures can be performed with the Reply Mode
carrying {4, 2}. When LSP Traceroute is issued, then following output Order TLV carrying {4, 2}. When LSP Traceroute is issued, then the
may be displayed without any unnecessary timeout. following output may be displayed without any unnecessary timeout:
Success (Reply from B, Reply Mode: 4) Success (Reply from B, Reply Mode: 4)
Success (Reply from C, Reply Mode: 4) Success (Reply from C, Reply Mode: 4)
Success (Reply from D, Reply Mode: 4) Success (Reply from D, Reply Mode: 4)
FEC Mismatch (Reply from F, Reply Mode: 2) FEC Mismatch (Reply from F, Reply Mode: 2)
Complete Complete
The result provides more diagnostic information to the initiator LSR, The result provides more diagnostic information to the initiator LSR,
and without any delay (i.e. timeout from one or more downstream and without any delay (i.e., timeout from one or more downstream
LSRs). LSRs).
A.2. Non-Co-Routed Bidirectional LSP Scenario A.2. Non-Co-Routed Bidirectional LSP Scenario
As shown in Figure 3, a network has a bidirectional LSP where the As shown in Figure 3, a network has a bidirectional LSP where the
forward LSP and the reverse LSP are not fully co-routed. forward LSP and the reverse LSP are not fully co-routed.
+----C------D----+ +----C------D----+
/ \ / \
A------B G------H A------B G------H
\ / \ /
+----E------F----+ +----E------F----+
Forward Paths: A-B-C-D-G-H (upper path) Forward Path: A-B-C-D-G-H (upper path)
Reverse Paths: H-G-F-E-B-A (lower path) Reverse Path: H-G-F-E-B-A (lower path)
Figure 3: Non-Co-Routed Bidirectional LSP Figure 3: Non-Co-Routed Bidirectional LSP
Some operators may prefer and configure the system to default the Some operators may prefer and configure "Reply via Specified Path" as
Reply Mode to indicate the reverse LSP when MPLS echo request the default Reply Mode but without including the Reply Path TLV, to
messages are sent on bidirectional LSPs. Without extensions indicate that the reverse LSP is used as the return path when MPLS
described in this document, following behaviors will be seen: echo request messages are sent on bidirectional LSPs. Without the
extensions described in this document, the following behaviors will
be seen:
o When LSP Ping is issued from A, the reply will come back on the o When LSP Ping is issued from A, the reply will come back on the
reverse LSP from H. reverse LSP from H.
o When LSP Traceroute is issued from A, the replies will come back o When LSP Traceroute is issued from A, the replies will come back
on the reverse LSP from B, G and H, but will encounter a timeout on the reverse LSP from B, G, and H but will encounter a timeout
from C and D as there are no reverse LSP on those nodes. from C and D, as there are no reverse LSPs on those nodes.
o When LSP Ping with specific TTL value is issued from A, whether a o When LSP Ping with a specific TTL value is issued from A, whether
timeout will be encountered depends on the value of the TTL used a timeout will be encountered depends on the value of the TTL used
(i.e. whether or not the MPLS echo request terminates on a node (i.e., whether or not the MPLS echo request terminates on a node
that has reverse LSP). that has a reverse LSP).
One can argue that the initiator LSR can automatically generate the One can argue that the initiator LSR can automatically generate the
same MPLS echo request with different Reply Mode value to those nodes same MPLS echo request with a different Reply Mode value to those
that timeout. However, such mechanism will result in extended time nodes that time out. However, such a mechanism will result in an
for the entire operation to complete (i.e. multiple seconds to extended time for the entire operation to complete (i.e., multiple
multiple minutes). This is undesirable, and perhaps unacceptable if seconds to multiple minutes). This is undesirable, and perhaps
the "user" is an application. unacceptable if the "user" is an application.
With the extension described in this document, same procedures can be With the extensions described in this document, the same procedures
performed with the Reply Mode Order TLV carrying {5, 2}. When LSP can be performed with the Reply Mode Order TLV carrying {5, 2}. When
Traceroute is issued, then following output may be displayed without LSP Traceroute is issued, then the following output may be displayed
any unnecessary timeout. without any unnecessary timeout:
Success (Reply Mode: 5) Success (Reply Mode: 5)
Success (Reply Mode: 2) Success (Reply Mode: 2)
Success (Reply Mode: 2) Success (Reply Mode: 2)
Success (Reply Mode: 5) Success (Reply Mode: 5)
Success (Reply Mode: 5) Success (Reply Mode: 5)
Complete Complete
Acknowledgements
The authors especially thank Tom Taylor, who passed away close to the
time of publication of this RFC. Tom did a careful review of the
document and provided useful comments.
The authors would also like to thank Santiago Alvarez and Faisal
Iqbal for discussions that motivated the creation of this document;
Sam Aldrin, Curtis Villamizar, Ross Callon, Jeffrey Zhang, Jeremy
Whittaker, Mustapha Alissaoui, Qin Wu, Jie Dong, and Adrian Farrel
for providing valuable comments that influenced the content of the
document; and Dan Frost, Victor Kuarsingh, and Deborah Brungard for
reviewing the document and providing useful comments.
Contributors
Shaleen Saxena
Brocade
Email: ssaxena@brocade.com
Authors' Addresses Authors' Addresses
Nobo Akiya Nobo Akiya
Big Switch Networks Big Switch Networks
Email: nobo.akiya.dev@gmail.com Email: nobo.akiya.dev@gmail.com
George Swallow George Swallow
Cisco Systems Cisco Systems
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