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SPRING Working Group                                           G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                             May 8, 2017
Expires: November 9, 2017


  Bidirectional Forwarding Detection (BFD) in Segment Routing Networks
                          Using MPLS Dataplane
                       draft-mirsky-spring-bfd-00

Abstract

   Segment Routing architecture leverages the paradigm of source
   routing.  It can be realized in the Multiprotocol Label Switching
   (MPLS) network without any change to the data plane.  A segment is
   encoded as an MPLS label and an ordered list of segments is encoded
   as a stack of labels.  Bidirectional Forwarding Detection (BFD) is
   expected to monitor any kind of paths between systems.  This document
   defines how to use Label Switched Path Ping to bootstrap and control
   path in reverse direction of a BFD session on the Segment Routing
   network over MPLS dataplane.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on November 9, 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
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   (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
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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 . . . . . . . . . . . .   2
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   2
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Bootstrapping BFD session over Segment Routed tunnel  . . . .   3
   3.  Use BFD Reverse Path TLV over Segment Routed MPLS tunnel  . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [RFC5880], [RFC5881], and [RFC5883] established the Bidirectional
   Forwarding Detection (BFD) protocol for IP networks.  [RFC5884] and
   [RFC7726] set rules of using BFD Asynchronous mode over Multiprotocol
   Label Switching (MPLS) Label Switched Path (LSP).  These latter
   standards implicitly assume that the egress BFD peer, which is the
   egress Label Edge Router (LER), will use the shortest path route
   regardless of the path the ingress LER uses to send BFD control
   packets towards it.

   This document defines use of LSP Ping for Segment Routing networks
   over MPLS dataplane [I-D.ietf-mpls-spring-lsp-ping] to bootstrap and
   control path of a BFD session from the egress to ingress LER.

1.1.  Conventions used in this document

1.1.1.  Terminology

   BFD: Bidirectional Forwarding Detection

   FEC: Forwarding Equivalence Class

   MPLS: Multiprotocol Label Switching

   LSP: Label Switching Path

   LER: Label Edge Router



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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.  Bootstrapping BFD session 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 Forwarding Equivalence
   Class (FEC) TLV.  Section 6.1 addresses use of the new sub-TLVs in
   Target FEC TLV in LSP ping and 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.

   It has been noted in [RFC5884] that a BFD session monitors for
   defects particular <MPLS LSP, FEC> tuple.  [RFC7726] clarified how to
   establish and operate mutiple BFD sessions for the same <MPLS LSP,
   FEC> tuple.  Because only ingress edge router is aware of the SR-
   based explicit route egress edge router can associate the LSP ping
   with BFD Discriminator TLV with only one of the FECs it advertised
   for the particular segment.  Thus this document defines that: When
   LSP ping is used to bootstrap a BFD session this document updates the
   statement and defines that:

      When LSP Ping is used to bootstrap a BFD session it MUST include
      only one 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.

   Encapsulation of a BFD Control packet in Segment Routing network with
   MPLS dataplane MUST follow Section 7 [RFC5884] when IP/UDP header
   used and MUST follow Section 3.4 [RFC6428] without IP/UDP header
   being used.




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3.  Use BFD Reverse Path TLV over Segment Routed MPLS tunnel

   When a BFD session is used to monitor a source 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 by using the BFD
   Reverse Path TLV [I-D.ietf-mpls-bfd-directed].  For the case of MPLS
   dataplane, Segment Routing Architecture
   [I-D.ietf-spring-segment-routing] explains that "a segment is encoded
   as an MPLS label.  An ordered list of segments is encoded as a stack
   of labels."  Following on that this document defines Segment Routing
   with MPLS dataplane sub-TLV that MAY be used with the BFD Reverse
   Path TLV [I-D.ietf-mpls-bfd-directed].  The format of the sub-TLV is
   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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  SegRouting MPLS sub-TLV Type |          Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Label Entry 1                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Label Entry 2                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                             ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Label Entry N                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


               Figure 1: Segment Routing MPLS Tunnel sub-TLV

   The Segment Routing Tunnel sub-TLV Type is two octets in length, and
   has a value of TBD (to be assigned by IANA as requested in
   Section 4).

   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.

   Exactly one Segment Routing Tunnel sub-TLV MUST be included in the
   Reverse Path TLV.  If more than one Segment Routing Tunnel 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" [I-D.ietf-mpls-bfd-directed]





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

4.  IANA Considerations

   The IANA is requested to assign new sub-TLV type 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 (TBD) | Segment Routing MPLS Tunnel sub-TLV | This document |
     +---------+-------------------------------------+---------------+

                Table 1: New Segment Routing Tunnel sub-TLV

5.  Security Considerations

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

6.  Acknowledgements

   TBD

7.  Normative References

   [I-D.ietf-mpls-bfd-directed]
              Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Directed Return
              Path", draft-ietf-mpls-bfd-directed-06 (work in progress),
              April 2017.

   [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-02 (work in
              progress), December 2016.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-11 (work in progress), February
              2017.




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   [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>.

   [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>.

   [RFC6428]  Allan, D., Ed., Swallow, G., Ed., and J. Drake, Ed.,
              "Proactive Connectivity Verification, Continuity Check,
              and Remote Defect Indication for the MPLS Transport
              Profile", RFC 6428, DOI 10.17487/RFC6428, November 2011,
              <http://www.rfc-editor.org/info/rfc6428>.

   [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>.






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Author's Address

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com













































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