[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 draft-ietf-mpls-bfd-directed

MPLS Working Group                                             G. Mirsky
Internet-Draft                                               J. Tantsura
Intended status: Standards Track                                Ericsson
Expires: February 9, 2016                                  I. Varlashkin
                                                                  Google
                                                                 M. Chen
                                                                  Huawei
                                                          August 8, 2015


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

Abstract

   Bidirectional Forwarding Detection (BFD) is expected to monitor bi-
   directional paths.  When a BFD session monitors in its forward
   direction an explicitly routed path there is a need to be able to
   direct egress BFD peer to use specific path as 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 February 9, 2016.

Copyright Notice

   Copyright (c) 2015 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



Mirsky, et al.          Expires February 9, 2016                [Page 1]


Internet-Draft          BFD Directed Return Path             August 2015


   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.  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 Tunnel sub-TLV  . . . . . . . . . . .   5
     3.2.  Case of IPv6 Data Plane . . . . . . . . . . . . . . . . .   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 . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .   8
   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.  All
   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.  As result, if the ingress BFD peer sends
   its BFD control packets over explicit path that is diverging from the
   best route, then reverse direction of the BFD session is likely not
   to be on co-routed bi-directional path with the forward direction of
   the BFD session.  And because BFD control packets are not guaranteed
   to cross the same links and nodes in both directions detection of
   Loss of Continuity (LoC) defect in forward direction may demonstrate
   positive negatives.





Mirsky, et al.          Expires February 9, 2016                [Page 2]


Internet-Draft          BFD Directed Return Path             August 2015


   This document defines the extension to LSP Ping [RFC4379], BFD
   Reverse Path TLV, 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 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
   direction between two nodes is likely to be co-routed, this
   fulfilling the implicit BFD requirements.  If BFD is used to monitor
   unidirectional explicitly routed paths, e.g.  MPLS-TE LSPs, its
   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 problems detecting
   failures on the unidirectional explicit path:

   o  detection of a failure on the reverse path cannot reliably be
      interpreted as bi-directional defect and thus trigger, for
      example, protection switchover of the forward direction;

   o  if a failure of the reverse path had been ignored, the ingress
      node would not receive indication of forward direction failure
      from its egress peer.




Mirsky, et al.          Expires February 9, 2016                [Page 3]


Internet-Draft          BFD Directed Return Path             August 2015


   To address these challenges the egress BFD peer should be instructed
   to use specific path for its 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 reverse path for the
   specified in BFD Discriminator TLV session.

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 the specified path that BFD control
   packets of the BFD session referenced in the BFD Discriminator TLV
   are required to follow.  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 value to be
   assigned by IANA.

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

   Reverse Path field contains a sub-TLV.  Any Target FEC sub-TLV,
   already or in the future defined, from IANA sub-registry Sub-TLVs for
   TLV Types 1, 16, and 21 of MPLS LSP Ping Parameters registry MAY be



Mirsky, et al.          Expires February 9, 2016                [Page 4]


Internet-Draft          BFD Directed Return Path             August 2015


   used in this field.  Only one sub-TLV MUST be included in the Reverse
   Path TLV.  If more than one sub-TLVs are present in the Reverse Path
   TLV, then only the first sub-TLV MUST be used and the rest MUST be
   silently discarded.

   If the egress LSR cannot find 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 LSR
   MAY establish the BFD session over IP network according to [RFC5884].

3.1.2.  Static and RSVP-TE sub-TLVs

   When explicit path on MPLS data plane set either as Static or RSVP-TE
   LSP respective sub-TLVs defined in [RFC7110] identify explicit return
   path.

3.1.3.  Segment Routing Tunnel sub-TLV

   In addition to Static and RSVP-TE, Segment Routing with MPLS data
   plane can be used to set 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
   will be allocated by IANA.

   The egress LSR MUST use the Value field as label stack for BFD
   control packets for the BFD session identified by source IP address
   and value in BFD Discriminator TLV.





Mirsky, et al.          Expires February 9, 2016                [Page 5]


Internet-Draft          BFD Directed Return Path             August 2015


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

3.2.  Case of IPv6 Data Plane

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

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 MPLS data plane adds three new
   sub-TLVs that may be used with Target FEC TLV.  Section 6.1 addresses
   use of new sub-TLVs in Target FEC TLV in LSP ping and 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.  "



Mirsky, et al.          Expires February 9, 2016                [Page 6]


Internet-Draft          BFD Directed Return Path             August 2015


   When LSP ping is used to bootstrap BFD session this document updates
   this 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 segment 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
   MAY precede the LSP ping that bootstraps the BFD session.

3.4.  Return Codes

   This document defines the following Return Codes:

   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 LSR, 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 LSR .
      (Section 3.1.1)

4.  Use Case Scenario

   In 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 BFD session to monitor
   the first tunnel, node A MUST include BFD Discriminator TLV with
   Discriminator value foobar-1 and MAY include BFD Reverse Path TLV
   that references H-G-D-C-B-A tunnel.  To bootstrap BFD session to
   monitor the second tunnel, node A MUST include BFD Discriminator TLV
   with Discriminator value foobar-2
   [I-D.ietf-bfd-rfc5884-clarifications] and MAY include BFD Reverse
   Path TLV that references H-G-F-E-B-A tunnel.

           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 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 existing BFD sessions.

5.  IANA Considerations







Mirsky, et al.          Expires February 9, 2016                [Page 7]


Internet-Draft          BFD Directed Return Path             August 2015


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

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) | Failed to establish the BFD session.   | This document |
   |          | The specified reverse path was not     |               |
   |          | found.                                 |               |
   +----------+----------------------------------------+---------------+

                         Table 3: New Return Code




Mirsky, et al.          Expires February 9, 2016                [Page 8]


Internet-Draft          BFD Directed Return Path             August 2015


6.  Security Considerations

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

7.  Acknowledgements

8.  Normative References

   [I-D.ietf-bfd-rfc5884-clarifications]
              Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
              Aldrin, "Clarifications to RFC 5884", draft-ietf-bfd-
              rfc5884-clarifications-02 (work in progress), June 2015.

   [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-04 (work
              in progress), July 2015.

   [I-D.previdi-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Field, B., Leung, I., Vyncke,
              E., and D. Lebrun, "IPv6 Segment Routing Header (SRH)",
              draft-previdi-6man-segment-routing-header-07 (work in
              progress), July 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>.

   [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>.






Mirsky, et al.          Expires February 9, 2016                [Page 9]


Internet-Draft          BFD Directed Return Path             August 2015


   [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>.

Authors' Addresses

   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com


   Jeff  Tantsura
   Ericsson

   Email: jeff.tantsura@ericsson.com


   Ilya Varlashkin
   Google

   Email: Ilya@nobulus.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com








Mirsky, et al.          Expires February 9, 2016               [Page 10]


Html markup produced by rfcmarkup 1.121, available from https://tools.ietf.org/tools/rfcmarkup/