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Versions: (draft-mirsky-mpls-bfd-directed) 00 01 02 03 04 05 06 07 08 09 10

MPLS Working Group                                             G. Mirsky
Internet-Draft                                               J. Tantsura
Intended status: Standards Track                                Ericsson
Expires: September 3, 2016                                 I. Varlashkin
                                                                  Google
                                                                 M. Chen
                                                                  Huawei
                                                           March 2, 2016


     Bidirectional Forwarding Detection (BFD) Directed Return Path
                    draft-ietf-mpls-bfd-directed-02

Abstract

   Bidirectional Forwarding Detection (BFD) is expected to monitor bi-
   directional paths.  When a BFD session monitors an explicit routed
   path there is a need to be able to direct egress BFD peer to use
   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
   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 September 3, 2016.

Copyright Notice

   Copyright (c) 2016 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



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   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.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Direct Reverse BFD Path . . . . . . . . . . . . . . . . . . .   4
     3.1.  Case of MPLS Data Plane . . . . . . . . . . . . . . . . .   4
       3.1.1.  BFD Reverse Path TLV  . . . . . . . . . . . . . . . .   4
       3.1.2.  Static and RSVP-TE sub-TLVs . . . . . . . . . . . . .   5
       3.1.3.  Segment Routing: MPLS Data Plane Case . . . . . . . .   5
     3.2.  Segment Routing: IPv6 Data Plane Case . . . . . . . . . .   6
     3.3.  Bootstrapping BFD session with BFD Reverse Path over
           Segment Routed tunnel . . . . . . . . . . . . . . . . . .   6
     3.4.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Use Case Scenario . . . . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   RFC 5880 [RFC5880], RFC 5881 [RFC5881], and RFC 5883 [RFC5883]
   established the BFD protocol for IP networks and RFC 5884 [RFC5884]
   set rules of using BFD asynchronous mode over IP/MPLS LSPs.  These
   four 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 an LSP is explicitly routed, if it is desired that
   BFD control packets follow the same path in the reverse direction
   (for support of common fault detection for explicitly routed
   bidirectional co-routed LSPs, for example), it is likely that the
   shortest return path to the ingress BFD peer may not follow the same
   path as the LSP in the forward direction.  The fact that BFD control
   packets are not guaranteed to cross the same links and nodes in both
   forward and reverse directions is a significant factor in producing




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   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 [RFC4379] and proposes that it to be used to instruct the egress
   BFD peer to use explicit path for its BFD control packets associated
   with the particular BFD session.  The TLV will be allocated from the
   TLV and sub-TLV registry defined by RFC 4379 [RFC4379].  As a special
   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.  Terminology

   BFD: Bidirectional Forwarding Detection

   MPLS: Multiprotocol Label Switching

   LSP: Label Switching Path

   LoC: Loss of Continuity

1.1.2.  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
   [RFC2119].

2.  Problem Statement

   BFD is best suited to monitor bi-directional co-routed paths.  In
   most cases, given stable environments, the forward and reverse
   directions between two nodes are likely to be co-routed, thus
   fulfilling the implicit BFD requirement.  If 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 still follow the shortest path route and that might
   lead to the following problem in detecting failures on a
   unidirectional explicit path:

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



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

3.  Direct Reverse BFD Path

3.1.  Case of MPLS Data Plane

   LSP ping, defined in [RFC4379], 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.

3.1.1.  BFD Reverse Path TLV

   The BFD Reverse Path TLV is an optional TLV within the LSP ping
   protocol.  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 [RFC4379].

   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
   TB1 (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



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   field.  Exactly one sub-TLV MUST be included in the Reverse Path TLV.
   If more than one sub-TLV is present in the Reverse Path TLV, then, in
   order to avoid ambiguity of which of TLVs to use, the egress BFD peer
   MUST send Echo Reply with the received Reverse Path TLVs and set the
   Return Code to "Too Many TLVs Detected" Section 3.4.

   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 3.4.  The egress BFD
   peer MAY establish the BFD session over IP network as defined in
   [RFC5884].

3.1.2.  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.

3.1.3.  Segment Routing: MPLS Data Plane Case

   In addition to Static and RSVP-TE, Segment Routing with MPLS data
   plane can be used to set an explicit path.  In this case a new sub-
   TLV is defined in this document as presented in Figure 2.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  SegRouting MPLS sub-TLV Type |          Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Label Entry 1                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Label Entry 2                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                             ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Label Entry N                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


               Figure 2: Segment Routing MPLS Tunnel sub-TLV

   The Segment Routing Tunnel sub-TLV Type is two octets in length, and
   has a value of TB2 (to be assigned by IANA as requested in
   Section 5).

   The egress LSR MUST use the Value field as label stack for BFD
   control packets for the BFD session identified by the source IP



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   address of the MPLS LSP Ping packet and the value in the BFD
   Discriminator TLV.  Label Entries MUST be in network order.

   The Segment Routing Tunnel sub-TLV MAY be used in Reply Path TLV
   defined in [RFC7110]

3.2.  Segment Routing: IPv6 Data Plane Case

   IPv6 can be used as the data plane of choice for Segment Routed
   tunnels [I-D.previdi-6man-segment-routing-header].  In this case the
   BFD Reverse Path TLV described in Section 3.1.1 can be used as well.
   To specify the reverse path of a BFD session for an IPv6 explicitly
   routed path the BFD Discriminator TLV MUST be used along with the BFD
   Reverse Path TLV.  The BFD Reverse Path TLV in IPv6 network MUST
   include the Segment Routing IPv6 Tunnel sub-TLV.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  SegRouting IPv6 sub-TLV Type |          Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                             |
    |                         IPv6 Prefix                         |
    |                                                             |
    |                                                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                             |
    |                         IPv6 Prefix                         |
    |                                                             |
    |                                                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                             ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 3: Segment Routing IPv6 Tunnel sub-TLV

   The Segment Routing IPv6 Tunnel sub-TLV Type is two octets in length,
   and has a value of TB3 (to be assigned by IANA as requested in
   Section 5).

3.3.  Bootstrapping BFD session with BFD Reverse Path over Segment
      Routed tunnel

   As discussed in [I-D.kumarkini-mpls-spring-lsp-ping] introduction of
   Segment Routing network domains with an MPLS data plane adds three
   new sub-TLVs that MAY be used with Target FEC TLV.  Section 6.1
   addresses use of the new sub-TLVs in Target FEC TLV in LSP ping and




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   LSP traceroute.  For the case of LSP ping the
   [I-D.kumarkini-mpls-spring-lsp-ping] states that:

   "Initiator MUST include FEC(s) corresponding to the destination
   segment.  "

   "Initiator, i.e. ingress LSR, MAY include FECs corresponding to some
   or all of segments imposed in the label stack by the ingress LSR to
   communicate the segments traversed.  "

   When LSP ping is used to bootstrap BFD session this document updates
   the statement and defines that LSP Ping MUST include the FEC
   corresponding to the destination segment and SHOULD NOT include FECs
   corresponding to some or all of other segments imposed by the ingress
   LSR.  Operationally such restriction would not cause any problem or
   uncertainty as LSP ping with FECs corresponding to some or all
   segments or traceroute that validate the segment route MAY precede
   the LSP ping that bootstraps the BFD session.

3.4.  Return Codes

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

   o  "Too Many TLVs Detected", (TBD4).  When more than one Reverse Path
      TLV found in the recieved Echo Request by the egress BFD peer, an
      Echo Reply with the return code set to "Too Many TLVs Detected"
      MUST be sent to the ingress BFD peer Section 3.1.1.

   o  "Failed to establish the BFD session.  The specified reverse path
      was not found", (TBD5).  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 3.1.1.

4.  Use Case Scenario

   In the network presented in Figure 4 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.




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

                Figure 4: 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.  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.

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

                     Table 1: New BFD Reverse Type TLV

5.2.  Sub-TLV

   The IANA is requested to assign two new sub-TLV types from
   "Multiprotocol Label Switching Architecture (MPLS) Label Switched
   Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV
   Types 1, 16, and 21" sub-registry.

    +----------+-------------------------------------+---------------+
    | Value    | Description                         | Reference     |
    +----------+-------------------------------------+---------------+
    | X (TBD2) | Segment Routing MPLS Tunnel sub-TLV | This document |
    | X (TBD3) | Segment Routing IPv6 Tunnel sub-TLV | This document |
    +----------+-------------------------------------+---------------+

                Table 2: New Segment Routing Tunnel sub-TLV







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5.3.  Return Codes

   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) | Too Many TLVs Detected.                | This document |
   | X (TBD5) | Failed to establish the BFD session.   | This document |
   |          | The specified reverse path was not     |               |
   |          | found.                                 |               |
   +----------+----------------------------------------+---------------+

                         Table 3: New Return Code

6.  Security Considerations

   Security considerations discussed in [RFC5880], [RFC5884], and
   [RFC4379], apply to this document.

7.  Acknowledgements

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

8.  Normative References

   [I-D.kumarkini-mpls-spring-lsp-ping]
              Kumar, N., Swallow, G., Pignataro, C., Akiya, N., Kini,
              S., Gredler, H., and M. Chen, "Label Switched Path (LSP)
              Ping/Trace for Segment Routing Networks Using MPLS
              Dataplane", draft-kumarkini-mpls-spring-lsp-ping-05 (work
              in progress), January 2016.

   [I-D.previdi-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
              J., Kosugi, T., Vyncke, E., and D. Lebrun, "IPv6 Segment
              Routing Header (SRH)", draft-previdi-6man-segment-routing-
              header-08 (work in progress), October 2015.

   [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>.




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   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              DOI 10.17487/RFC4379, February 2006,
              <http://www.rfc-editor.org/info/rfc4379>.

   [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>.

   [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>.

Authors' Addresses

   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com






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   Jeff  Tantsura
   Ericsson

   Email: jeff.tantsura@ericsson.com


   Ilya Varlashkin
   Google

   Email: Ilya@nobulus.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com



































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