Internet Engineering Task Force N. Akiya
Internet-Draft G. Swallow
Updates: 4379 (if approved) C. Pignataro
Intended status: Standards Track Cisco Systems
Expires: June 18, 2014 L. Andersson
M. Chen
Huawei
December 15, 2013
Label Switched Path (LSP) Ping/Trace Reply Mode Simplification
draft-akiya-mpls-lsp-ping-reply-mode-simple-01
Abstract
This document adds one reply mode to indicate reverse LSP, to be used
by Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
Ping and Traceroute. This document also adds an optional TLV which
can carry ordered list of reply modes.
This document updates [RFC4379].
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 18, 2014.
Copyright Notice
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Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Statements . . . . . . . . . . . . . . . . . . . . . 3
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Reply via reverse LSP . . . . . . . . . . . . . . . . . . 4
3.2. Reply Mode Order TLV . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. New Reply Mode . . . . . . . . . . . . . . . . . . . . . 6
5.2. New Reply Mode Order TLV . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Contributing Authors . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
MPLS LSP Ping, described in [RFC4379], allows initiator to encode
instructions (Reply Mode) on how responder is to send response back
to the initiator. [I-D.ietf-mpls-return-path-specified-lsp-ping]
also allows initiator to encode a TLV (Reply Path TLV) which can
instruct responder to use specific LSP to send response back to the
initiator. Both approaches are powerful as they provide ability for
the initiator to control the return path.
It is, however, becoming increasingly difficult for an initiator to
select the "right" return path to encode in MPLS LSP echo request
packets. Consequence of initiator not selecting the "right" return
path encoding can result in false failure of MPLS LSP Ping and
Traceroute operations, due to initiator not receiving back expected
MPLS LSP echo reply. Resulting from an effort to minimize such false
failures, implementations may result in having different "default"
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return path encoding per LSP type and per operational type.
Deviating "default" return path encoding, potentially, per vendor per
LSP type per operational type can drift this technology from
consistency axle. Thus it is desirable to have a return path
encoding mechanism which minimizes false failure scenarios while
reverse direction taking path preferred for operational needs.
2. Problem Statements
It is becoming increasingly difficult for implementations to
automatically supply a workable return path encoding for all MPLS LSP
Ping and Traceroute operations across all LSP types. There are
several factors which are contributing to this complication.
o Some LSPs have control-channel, and some do not. Some LSPs have
reverse LSP, and some do not. Some LSPs have IP route in reverse
direction, and some do not.
o LSRs on some LSPs can have different available return path(s).
Available return path(s) can depend on whether responder is a
transit LSR or an egress LSR. In case of bi-directional LSP,
available return path(s) on transit LSRs can also depend on
whether LSP is completely co-routed, partially co-routed or non-
co-routed.
o MPLS LSP echo request packets may falsely terminate on an
unintended target which can have different available return
path(s) than intended target.
o MPLS LSP Ping operation is expected to terminate on egress LSR.
However, MPLS LSP Ping operation with specific TTL values and MPLS
LSP Traceroute operation can terminate on both transit LSR(s) and
egress LSR.
Except for the case where responder node does not have an IP route
back to the initiator, it is possible to use Reply Mode of value 2
(Reply via an IPv4/IPv6 UDP packet) in all cases. However, some
operators are preferring control-channel and reverse LSP as "default"
return path if they are available, which are not always available.
When specific return path encoding is being supplied by users or
applications, then there are no issues in choosing the return path
encoding. When specific return path encoding is not being supplied
by users or applications, then implementations require extended logic
to compute, and sometimes "guess", the "default" return path
encodings. If a responder received a MPLS LSP echo request
containing return path instruction which cannot be accommodated due
to unavailability, then responder implementations often drop such
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packets. This results in initiator to not receive back MPLS LSP echo
reply packets. Consequence may be acceptable for failure cases (ex:
broken LSP) where MPLS LSP echo request terminated on unintended
target. However, initiator not receiving back MPLS LSP echo reply
packets, even when intended target received and verified the
requests, is not desirable as result will be conveyed as false
failures to users.
Some return path(s) are more preferred than others, but preferred
cannot be used in all cases. Thus implementations are required to
compute when preferred return path encoding can and cannot be used,
and that computation is becoming more and more difficult.
This document adds one Reply Mode to describe reverse LSP, and one
optional TLV to describe ordered list of reply modes. Based on
operational needs, the TLV can describe multiple Reply Mode values in
preferred order to allow responder to use first available Reply Mode
from the list. This eliminates the need for initiator to compute, or
sometimes "guess", the "default" return path encoding. And that will
result in simplified implementations across vendors, and result in
improved usability to fit operational needs.
3. Solution
This document adds one reply mode to indicate reverse LSP, to be used
by Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
Ping and Traceroute. This document also adds an optional TLV which
can carry ordered list of reply modes.
3.1. Reply via reverse LSP
Some LSP types are capable of having related LSP in reverse
direction, through signaling or other association mechanisms. This
document uses the term "Reverse LSP" to refer to the LSP in reverse
direction of such LSP types. Note that this document isolates the
scope of "Reverse LSP" applicability to those reverse LSPs which are
capable of and permitted to carry the IP encapsulated MPLS LSP echo
reply.
This document adds one Reply Mode to be used by MPLS LSP Ping and
Traceroute operations.
Value Meaning
----- -------
TBD1 Reply via reverse LSP
MPLS LSP echo request with TBD1 (Reply via reverse LSP) in the Reply
Mode field may be used to instruct responder to use reverse LSP to
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send MPLS LSP echo reply. Reverse LSP is in relation to the last FEC
specified in the Target FEC Stack TLV.
When responder is using this Reply Mode, transmitting MPLS LSP echo
reply packet MUST use IP destination address of 127/8 for IPv4 and
0:0:0:0:0:FFFF:7F00/104 for IPv6.
3.2. Reply Mode Order TLV
This document also introduces a new optional TLV to describe list of
Reply Mode values. The new TLV will contain one or more Reply Mode
value(s) in preferred order, first Reply Mode value appearing being
most preferred. Following rules apply when using Reply Mode Order
TLV.
1. Reply Mode Order TLV MAY be included in MPLS echo request.
2. Reply Mode Order TLV MUST NOT be included in MPLS echo reply.
3. Reply Mode field of MPLS echo request MUST be set to a valid
value when supplying Reply Mode Order TLV in transmitting MPLS
echo request. It is RECOMMENDED for initiator to set Reply Mode
field of MPLS echo request to a value that corresponds to return
path most likely to be available, in case responder does not
understand the Reply Mode Order TLV.
4. If responder node understands Reply Mode Order TLV and TLV is
valid, then responder MUST consider Reply Mode values described
in the TLV and MUST NOT use value described in Reply Mode field
of received MPLS echo request.
5. If responder node understands Reply Mode Order TLV but TLV is not
valid (due to conditions listed below), then responder MUST only
use value described in Reply Mode field of received MPLS echo
request.
6. Reply Mode Order TLV MUST contain at least one Reply Mode value,
and SHOULD contain at least two Reply Mode values.
7. Same Reply Mode value MUST NOT appear multiple times in the Reply
Mode Order TLV.
8. Reply Mode value 1 (Do not reply) SHOULD NOT be used in the Reply
Mode Order TLV.
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The responding node is to select the first available return path in
this TLV. Reply Mode value corresponding to selected return path
MUST be set in Reply Mode field of MPLS LSP echo reply to communicate
back to the initiator which return path was chosen.
The format of the TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Mode Order TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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. Each Reply Mode field is 1
octet.
4. Security Considerations
Beyond those specified in [RFC4379], there are no further security
measures required.
5. IANA Considerations
5.1. New Reply Mode
IANA is requested to assign one reply modes from the "Reply Mode"
sub-registry within the "Multiprotocol Label Switching Architecture
(MPLS)" registry.
Value Meaning Reference
----- ------- ---------
TBD1 Reply via reverse LSP this document
5.2. New Reply Mode Order TLV
IANA is requested to assign a new TLV type value from the "TLVs" sub-
registry within the "Multiprotocol Label Switching Architecture
(MPLS)" registry, for the "Reply Mode Order TLV".
The new TLV Type value should be assigned from the range
(32768-49161) specified in RFC 4379 [RFC4379] section 3 that allows
the TLV type to be silently dropped if not recognized.
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Type Meaning Reference
---- ------- ---------
TBD2 Reply Mode Order TLV this document
6. Acknowledgements
Authors would like to thank Santiago Alvarez and Faisal Iqbal for
discussions which motivated creation of this document. Authors would
also like to thank Sam Aldrin and Curtis Villamizar for providing
valuable comments to influence the contents of the draft.
7. Contributing Authors
Shaleen Saxena
Cisco Systems
Email: ssaxena@cisco.com
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
8.2. Informative References
[I-D.ietf-mpls-return-path-specified-lsp-ping]
Chen, M., Cao, W., Ning, S., JOUNAY, F., and S. DeLord,
"Return Path Specified LSP Ping", draft-ietf-mpls-return-
path-specified-lsp-ping-15 (work in progress), October
2013.
Authors' Addresses
Nobo Akiya
Cisco Systems
Email: nobo@cisco.com
George Swallow
Cisco Systems
Email: swallow@cisco.com
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Carlos Pignataro
Cisco Systems
Email: cpignata@cisco.com
Loa Andersson
Huawei
Email: loa@mail01.huawei.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
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