Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-ietf-mpls-bfd-directed-04

MPLS Working Group                                             G. Mirsky
Internet-Draft                                                  Ericsson
Intended status: Standards Track                             J. Tantsura
Expires: March 18, 2017                                       Individual
                                                           I. Varlashkin
                                                                  Google
                                                                 M. Chen
                                                                  Huawei
                                                      September 14, 2016

     Bidirectional Forwarding Detection (BFD) Directed Return Path
                    draft-ietf-mpls-bfd-directed-04

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 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
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   This Internet-Draft will expire on March 18, 2017.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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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.  Direct Reverse BFD Path . . . . . . . . . . . . . . . . . . .   3
     3.1.  Case of MPLS Data Plane . . . . . . . . . . . . . . . . .   3
       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.  Bootstrapping BFD session with BFD Reverse Path over
           Segment Routed tunnel . . . . . . . . . . . . . . . . . .   5
     3.3.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Use Case Scenario . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   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
   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

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   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 is to be used to instruct the
   egress BFD peer to use 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 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.  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

   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.  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.

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3.1.1.  BFD Reverse Path TLV

   The BFD Reverse Path TLV is an optional TLV within the LSP ping
   [RFC4379], [RFC6424].  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
   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.  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 3.3.

   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].

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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 TBD2 (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
   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.  Bootstrapping BFD session with BFD Reverse Path over Segment
      Routed tunnel

   As discussed in [I-D.ietf-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.ietf-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.

3.3.  Return Codes

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

   o  "Too Many TLVs Detected", (TBD3).  When more than one Reverse Path
      TLV found in the received 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", (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 3.1.1.

4.  Use Case Scenario

   In the network presented in Figure 3 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 3: 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 create new sub-registry for sub-TLV types of
   TLV TBD.  All code points in the ranges 0 through 16383 and 32768
   through 49161 in this registry shall be allocated according to the
   "IETF Review" procedure as specified in [RFC5226] . Code points in
   the ranges 16384 through 31743 and 49162 through 64511 in this
   registry shall be allocated according to the "First Come First
   Served" procedure as specified in [RFC5226].  Values in the range
   31744 through 32767 and 64512 through 65534 are for Vendor or Private
   Use, and MUST NOT be allocated.  This document defines the following
   new values of new sub-TLV type:

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   +-------------+-------------------------------------+---------------+
   | Value       | Description                         | Reference     |
   +-------------+-------------------------------------+---------------+
   | 0           | Reserved                            | This document |
   | X (TBD2)    | Segment Routing MPLS Tunnel sub-TLV | This document |
   | 2-31743     | Unassigned                          |               |
   | 31744-32767 | Reserved for Vendor or Private Use  |               |
   | 32768-64511 | Unassigned                          |               |
   | 64512-65534 | Reserved for Vendor or Private Use  |               |
   | 65535       | Reserved                            | This document |
   +-------------+-------------------------------------+---------------+

                Table 2: New Segment Routing Tunnel sub-TLV

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 (TBD3) | Too Many TLVs Detected.                | This document |
   | X (TBD4) | 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 and Carlos Pignataro.

8.  References

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8.1.  Normative References

   [I-D.ietf-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-ietf-mpls-spring-lsp-ping-00 (work in
              progress), May 2016.

   [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>.

   [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>.

   [RFC6424]  Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
              Performing Label Switched Path Ping (LSP Ping) over MPLS
              Tunnels", RFC 6424, DOI 10.17487/RFC6424, November 2011,
              <http://www.rfc-editor.org/info/rfc6424>.

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   [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>.

8.2.  Informative References

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

Authors' Addresses

   Greg Mirsky
   Ericsson

   Email: gregimirsky@gmail.com

   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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