BFD in Demand Mode over Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-11

BFD Working Group                                              G. Mirsky
Internet-Draft                                                  Ericsson
Intended status: Informational                              7 March 2022
Expires: 8 September 2022

            BFD in Demand Mode over Point-to-Point MPLS LSP
                    draft-mirsky-bfd-mpls-demand-11

Abstract

   This document describes procedures for using Bidirectional Forwarding
   Detection (BFD) in Demand mode to detect data plane failures in
   Multiprotocol Label Switching (MPLS) point-to-point Label Switched
   Paths.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Use of the BFD Demand Mode  . . . . . . . . . . . . . . . . .   2
     3.1.  The Applicability of BFD for Multipoint Networks  . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [RFC5884] defined use of the Asynchronous method of Bidirectional
   Detection (BFD) [RFC5880] to monitor and detect failures in the data
   path of a Multiprotocol Label Switching (MPLS) Label Switched Path
   (LSP).  Use of the Demand mode, also specified in [RFC5880], has not
   been defined so far.  This document describes procedures for using
   the Demand mode of BFD protocol to detect data plane failures in MPLS
   point-to-point (p2p) LSPs.

2.  Conventions used in this document

2.1.  Terminology

   MPLS: Multiprotocol Label Switching

   LSP: Label Switched Path

   LER: Label switching Edge Router

   BFD: Bidirectional Forwarding Detection

   p2p: Point-to-Point

3.  Use of the BFD Demand Mode

   [RFC5880] defines that the Demand mode may be:

   *  asymmetric, i.e. used in one direction of a BFD session;

   *  switched to and from without bringing BFD session to Down state
      through using a Poll Sequence.

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   For the case of BFD over MPLS LSP, ingress Label switching Edge
   Router (LER) usually acts as Active BFD peer and egress LER acts as
   Passive BFD peer.  The Active peer bootstraps the BFD session by
   using LSP ping.  If the BFD session is configured to use the Demand
   mode, once the BFD session is in Up state the ingress LER switches to
   the Demand mode as defined in Section 6.6 [RFC5880].  The egress LER
   also follows procedures defined in Section 6.6 [RFC5880] and ceases
   further transmission of periodic BFD control packets to the ingress
   LER.

   In this state BFD peers remains as long as the egress LER is in Up
   state.  The ingress LER can periodically check continuity of a
   bidirectional path between the ingress and egress LERs by using the
   Poll Sequence, as described in Section 6.6 [RFC5880].  An
   implementation that supports using the Poll Sequence as the mechanism
   for bidirectional path continuity check must control the interval
   between consecutive Poll Sequences.  The Rdefault value could be
   selected as 1 second.

   If the Detection timer at the egress LER expires, the BFD system on
   LER sends BFD Control packet to the ingress LER with the Poll (P) bit
   set, Status (Sta) field set to the Down value, and the Diagnostic
   (Diag) field set to Control Detection Time Expired value.  The egress
   LER periodically transmits these Control packets to the ingress LER
   until either it receives the valid for this BFD session control
   packet with the Final (F) bit set from the ingress LER or the defect
   condition clears and the BFD session state reaches Up state at the
   egress LER.  An implementation that supports this specification
   provides control of the interval between consecutive Poll messages
   signaling the expiration of the Detection timer.  The default value
   of the interval can be selected as 1 second.

   The ingress LER transmits BFD Control packets over the MPLS LSP with
   the Demand (D) flag set at negotiated interval per [RFC5880], the
   greater of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval,
   until it receives the valid BFD packet from the egress LER with the
   Poll (P) bit and the Diagnostic (Diag) field value Control Detection
   Time Expired.  Reception of such BFD control packet by the ingress
   LER indicates that the monitored LSP has a failure and sending BFD
   control packet with the Final flag set to acknowledge failure
   indication is likely to fail.  Instead, the ingress LER transmits the
   BFD Control packet to the egress LER over the IP network with:

   *  destination IP address is set to the destination IP address of the
      LSP Ping Echo request message [RFC8029];

   *  destination UDP port set to 4784 [RFC5883];

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   *  Final (F) flag in BFD control packet is set;

   *  Demand (D) flag in BFD control packet is cleared.

   The ingress LER changes the state of the BFD session to Down and
   changes rate of BFD Control packets transmission to one packet per
   second.  The ingress LER in Down mode changes to Asynchronous mode
   until the BFD session comes to Up state once again.  Then the ingress
   LER switches to the Demand mode.

3.1.  The Applicability of BFD for Multipoint Networks

   [RFC8562] defines the use of BFD in multipoint networks.  This
   specification analyzes the case of p2p LSP.  In that scenario, the
   ingress of the LSP acts as the MultipointHead, and the egress - as
   MultipointTail.  The BFD state machines for MultipointHead,
   MultipointClient, and MultipointTail don't use the three-way
   handshakes for session establishment and teardown.  As a result, the
   Init state is absent, and the session transitions to the Up state
   once the BFD session is administratively enabled.  Hence, a BFD
   session over a p2p LSP, using principles of [RFC8562] or [RFC8563],
   can be established faster if the MultipointTail has been provisioned
   with the value of My Discriminator used by the MultipointHead for
   that BFD session.  That value can be provided to the MultipointTail
   using different mechanisms, e.g., an extension to IGP.  Description
   of mechanism to provide the value of My Discriminator used by the
   MultipointHead for the particular BFD session is outside the scope of
   this specification.

   Unsolicited notification of the detected failure by the
   MultipointTail to the MultipointClient performs as described above
   for the case when the ingress BFD system switches the remote peer
   into the Demand mode.

4.  IANA Considerations

   TBD

5.  Security Considerations

   This document does not introduce new security aspects but inherits
   all security considerations from [RFC5880], [RFC5884], [RFC7726],
   [RFC8029], and [RFC6425].

6.  Normative References

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

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <https://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, <https://www.rfc-editor.org/info/rfc5884>.

   [RFC6425]  Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
              Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
              Failures in Point-to-Multipoint MPLS - Extensions to LSP
              Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
              <https://www.rfc-editor.org/info/rfc6425>.

   [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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC8562]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) for
              Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
              April 2019, <https://www.rfc-editor.org/info/rfc8562>.

7.  Informative References

   [RFC8563]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
              Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
              <https://www.rfc-editor.org/info/rfc8563>.

Appendix A.  Acknowledgements

   TBD

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Author's Address

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

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