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Versions: 00 01 02 03 draft-ietf-mpls-lsp-ping-reply-mode-simple

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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   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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