BFD in Demand Mode over a Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-15

BFD Working Group                                              G. Mirsky
Internet-Draft                                                  Ericsson
Intended status: Informational                           9 November 2023
Expires: 12 May 2024

           BFD in Demand Mode over a Point-to-Point MPLS LSP
                    draft-mirsky-bfd-mpls-demand-15

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.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Use of the BFD Demand Mode  . . . . . . . . . . . . . . . . .   2
     3.1.  The Applicability of BFD for Multipoint Networks  . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

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.  Acronyms

   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.

   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

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   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 remain 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 default value could be
   selected as 1 second.

   If the Detection Time at the egress LER expires, the session state on
   the egress LER transitions to the Down state according to Section 6.2
   of [RFC5880].  As a result, the BFD system exits the Demand mode and
   sends the BFD Control packet to the ingress LER with the Status (Sta)
   field set to the Down (1) value and the Diagnostic (Diag) field set
   to Control Detection Time Expired (1) value.  The egress LER
   periodically transmits these Control packets to the ingress LER until
   either it receives the valid BFD control packet from the ingress LER.
   The interval between BFD control packets is determined according to
   Section 6.8.7 of [RFC5880].

   The ingress LER transmits BFD Control packets over the MPLS LSP with
   the Demand (D) flag set at the negotiated interval per [RFC5880].  If
   it receives the valid BFD packet from the egress LER with the Status
   (Sta) field set to Down and the Diagnostic (Diag) field value Control
   Detection Time Expired, the ingress LER indicates that the monitored
   LSP has a failure.  Consequently, the BFD system on the ingress LER
   advances the state of the BFD session to the Init state and sends a
   BFD control packet with the Demand (D) flag cleared.  That packet is
   transmitted periodically.  The BFD system continues performing in the
   BFD Asynchronous mode until the BFD session reaches the Up state.
   Then the ingress LER switches to the Demand mode.

3.1.  The Applicability of BFD for Multipoint Networks

   [RFC8562] and [RFC8563] define 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],

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   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 in
   Section 3 for the case after the ingress BFD system switches the
   remote peer into the Demand mode.

4.  IANA Considerations

   This document doesn't require any IANA action.  This section can be
   removed before the publication of the document.

5.  Security Considerations

   This document does not introduce new security aspects but inherits
   all security considerations from [RFC5880], [RFC5884], [RFC7726],
   [RFC8029], [RFC6425], [RFC8562], and [RFC8563]

6.  Acknowledgements

   The author expresses his genuine appreciation of the extensive
   technical comments and the discussion with Jeffrey Haas that helped
   to clarify and properly position this document relative to the
   existing BFD specifications.

7.  Normative References

   [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>.

   [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>.

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   [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>.

   [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>.

Author's Address

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

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