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Versions: (draft-mirsky-mpls-bfd-directed) 00 01 02 03 04 05 06 07

MPLS Working Group                                             G. Mirsky
Internet-Draft                                                       ZTE
Intended status: Standards Track                             J. Tantsura
Expires: December 15, 2017                                    Individual
                                                           I. Varlashkin
                                                                  Google
                                                                 M. Chen
                                                                  Huawei
                                                           June 13, 2017


     Bidirectional Forwarding Detection (BFD) Directed Return Path
                    draft-ietf-mpls-bfd-directed-07

Abstract

   Bidirectional Forwarding Detection (BFD) is expected to be able to
   monitor wide variety of encapsulations of paths between systems.
   When a BFD session monitors an explicitly routed unidirectional path
   there may be a need to direct egress BFD peer to use a specific path
   for the reverse direction of the BFD session.

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
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   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 December 15, 2017.

Copyright Notice

   Copyright (c) 2017 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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   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
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
       1.1.1.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Control of the Reverse BFD Path . . . . . . . . . . . . . . .   3
     3.1.  BFD Reverse Path TLV  . . . . . . . . . . . . . . . . . .   3
     3.2.  Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . . .   4
     3.3.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Use Case Scenario . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  BFD Reverse Path TLV  . . . . . . . . . . . . . . . . . .   5
     5.2.  Return Code . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [RFC5880], [RFC5881], and [RFC5883] established the BFD protocol for
   IP networks.  [RFC5884] and [RFC7726] set rules of using BFD
   asynchronous mode over IP/MPLS LSPs.  These standards implicitly
   assume that the egress BFD peer will use the shortest path route
   regardless of route being used to send BFD control packets towards
   it.

   For the case where a LSP is explicitly routed it is likely that the
   shortest return path to the ingress BFD peer would not follow the
   same path as the LSP in the forward direction.  The fact that BFD
   control packets are not guaranteed to follow the same links and nodes
   in both forward and reverse directions is a significant factor in
   producing false positive defect notifications, i.e. false alarms, if
   used by the ingress BFD peer to deduce the state of the forward
   direction.

   This document defines the BFD Reverse Path TLV as an extension to LSP
   Ping [RFC8029] and proposes that it is to be used to instruct the
   egress BFD peer to use an explicit path for its BFD control packets
   associated with a particular BFD session.  The TLV will be allocated
   from the TLV and sub-TLV registry defined in [RFC8029].  As a special



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   case, forward and reverse directions of the BFD session can form a
   bi-directional co-routed associated channel.

1.1.  Conventions used in this document

1.1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Problem Statement

   When BFD is used to monitor unidirectional explicitly routed path,
   e.g.  MPLS-TE LSP, BFD control packets in forward direction would be
   in-band using the mechanism defined in [RFC5884] and [RFC5586].  But
   the reverse direction of the BFD session would follow the shortest
   path route and that might lead to the problem in detecting failures
   on a unidirectional explicit path as described below:

   o  a failure detection by ingress node on the reverse path cannot be
      interpreted as bi-directional failure unambiguously and thus
      trigger, for example, protection switchover of the forward
      direction without possibility of being a false positive.

   To address this scenario the egress BFD peer would be instructed to
   use a specific path for BFD control packets.

3.  Control of the Reverse BFD Path

   LSP ping, defined in [RFC8029], uses BFD Discriminator TLV [RFC5884]
   to bootstrap a BFD session over an MPLS LSP.  This document defines a
   new TLV, BFD Reverse Path TLV, that MUST contain a single sub-TLV
   that can be used to carry information about the reverse path for the
   BFD session that is specified by value in BFD Discriminator TLV.

3.1.  BFD Reverse Path TLV

   The BFD Reverse Path TLV is an optional TLV within the LSP ping
   [RFC8029].  However, if used, the BFD Discriminator TLV MUST be
   included in an Echo Request message as well.  If the BFD
   Discriminator TLV is not present when the BFD Reverse Path TLV is
   included, then it MUST be treated as malformed Echo Request, as
   described in [RFC8029].





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   The BFD Reverse Path TLV carries information about the path onto
   which the egress BFD peer of the BFD session referenced by the BFD
   Discriminator TLV MUST transmit BFD control packets.  The format of
   the BFD Reverse Path TLV is as presented in Figure 1.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   BFD Reverse Path TLV Type |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Reverse Path                         |
    ~                                                             ~
    |                                                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: BFD Reverse Path TLV

   BFD Reverse Path TLV Type is 2 octets in length and has a value of
   TBD1 (to be assigned by IANA as requested in Section 5).

   Length field is 2 octets long and defines the length in octets of the
   Reverse Path field.

   Reverse Path field contains a sub-TLV.  Any Target FEC sub-TLV
   (already defined, or to be defined in the future) for TLV Types 1,
   16, and 21 of MPLS LSP Ping Parameters registry MAY be used in this
   field.  None, one or more sub-TLVs MAY be included in the BFD Reverse
   Path TLV.  If none sub-TLVs found in the BFD Reverse Path TLV, the
   egress BFD peer MUST revert to using the default, i.e., over IP
   network, reverse path.

   If the egress LSR cannot find the path specified in the Reverse Path
   TLV it MUST send Echo Reply with the received Reverse Path TLV and
   set the Return Code to "Failed to establish the BFD session.  The
   specified reverse path was not found" Section 3.3.  The egress BFD
   peer MAY establish the BFD session over IP network as defined in
   [RFC5884].

3.2.  Static and RSVP-TE sub-TLVs

   When an explicit path on an MPLS data plane is set either as Static
   or RSVP-TE LSP respective sub-TLVs defined in [RFC7110] MAY be used
   to identify the explicit reverse path for the BFD session.








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3.3.  Return Codes

   This document defines the following Return Codes for MPLS LSP Echo
   Reply:

   o  "Failed to establish the BFD session.  The specified reverse path
      was not found", (TBD4).  When a specified reverse path is not
      available at the egress BFD peer, an Echo Reply with the return
      code set to "Failed to establish the BFD session.  The specified
      reverse path was not found" MUST be sent back to the ingress BFD
      peer Section 3.1.

4.  Use Case Scenario

   In the network presented in Figure 2 node A monitors two tunnels to
   node H: A-B-C-D-G-H and A-B-E-F-G-H.  To bootstrap a BFD session to
   monitor the first tunnel, node A MUST include a BFD Discriminator TLV
   with Discriminator value (e.g. foobar-1) and MAY include a BFD
   Reverse Path TLV that references H-G-D-C-B-A tunnel.  To bootstrap a
   BFD session to monitor the second tunnel, node A MUST include a BFD
   Discriminator TLV with a different Discriminator value (e.g. foobar-
   2) [RFC7726] and MAY include a BFD Reverse Path TLV that references
   H-G-F-E-B-A tunnel.

           C---------D
           |         |
   A-------B         G-----H
           |         |
           E---------F

                Figure 2: Use Case for BFD Reverse Path TLV

   If an operator needs node H to monitor a path to node A, e.g.
   H-G-D-C-B-A tunnel, then by looking up list of known Reverse Paths it
   MAY find and use the existing BFD session.

5.  IANA Considerations

5.1.  BFD Reverse Path TLV

   The IANA is requested to assign a new value for BFD Reverse Path TLV
   from the "Multiprotocol Label Switching Architecture (MPLS) Label
   Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and
   sub-TLVs" sub-registry.







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            +----------+----------------------+---------------+
            | Value    | Description          | Reference     |
            +----------+----------------------+---------------+
            | X (TBD1) | BFD Reverse Path TLV | This document |
            +----------+----------------------+---------------+

                     Table 1: New BFD Reverse Type TLV

5.2.  Return Code

   The IANA is requested to assign a new Return Code value from the
   "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
   Ping Parameters" registry, "Return Codes" sub-registry, as follows
   using a Standards Action value.

   +----------+----------------------------------------+---------------+
   | Value    | Description                            | Reference     |
   +----------+----------------------------------------+---------------+
   | X (TBD4) | Failed to establish the BFD session.   | This document |
   |          | The specified reverse path was not     |               |
   |          | found.                                 |               |
   +----------+----------------------------------------+---------------+

                         Table 2: New Return Code

6.  Security Considerations

   Security considerations discussed in [RFC5880], [RFC5884], [RFC7726],
   and [RFC8029], apply to this document.

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <http://www.rfc-editor.org/info/rfc5586>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <http://www.rfc-editor.org/info/rfc5880>.






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   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <http://www.rfc-editor.org/info/rfc5881>.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <http://www.rfc-editor.org/info/rfc5883>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <http://www.rfc-editor.org/info/rfc5884>.

   [RFC7110]  Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
              "Return Path Specified Label Switched Path (LSP) Ping",
              RFC 7110, DOI 10.17487/RFC7110, January 2014,
              <http://www.rfc-editor.org/info/rfc7110>.

   [RFC7726]  Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
              Aldrin, "Clarifying Procedures for Establishing BFD
              Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726,
              DOI 10.17487/RFC7726, January 2016,
              <http://www.rfc-editor.org/info/rfc7726>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <http://www.rfc-editor.org/info/rfc8029>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <http://www.rfc-editor.org/info/rfc8174>.

Appendix A.  Acknowledgments

   Authors greatly appreciate thorough review and the most helpful
   comments from Eric Gray and Carlos Pignataro.

Authors' Addresses

   Greg Mirsky
   ZTE

   Email: gregimirsky@gmail.com





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   Jeff  Tantsura
   Individual

   Email: jefftant.ietf@gmail.com


   Ilya Varlashkin
   Google

   Email: Ilya@nobulus.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com



































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