PIM Working Group                                              G. Mirsky
Internet-Draft                                                 ZTE Corp.                                                  Ericsson
Intended status: Standards Track                               J. Xiaoli
Expires: 5 February 14 March 2022                                   ZTE Corporation
                                                           4 August
                                                       10 September 2021

   The Use of Bidirectional Forwarding Detection (BFD) for Multipoint

 Fast Failover in Protocol Independent Multicast - Sparse Mode (PIM-SM)
 Using Bidirectional Forwarding Detection (BFD) for Multipoint Networks


   This document specifies the use of how Bidirectional Forwarding Detection
   (BFD) for
   multipoint networks to can provide nodes sub-second failover for routers that
   participate in Protocol Independent Multicast - Sparse Mode (PIM-SM) with sub-second
   convergence. (PIM-SM).
   An extension to the PIM Hello message used to bootstrap
   point-to-multipoint a point-to-
   multipoint BFD sessions session is also defined in this document.

Status of This Memo

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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.  BFD Discriminator PIM Hello Option  . . . . . . . . . . . . .   3
     2.1.  Using P2MP BFD in PIM DR/BDR Router Monitoring . . . . . . . . .   4
     2.2.  P2MP BFD in PIM DR Load Balancing . . . . . . . . . . . .   5
     2.3.  Multipoint BFD Encapsulation  . . . . . . . . . . . . . .   5
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Faster convergence in the control plane, in general, is beneficial
   and allows minimizing periods of traffic blackholing, transient
   routing loops, and other scenarios that may negatively affect service
   data flow.  That equally applies to unicast and multicast routing

   [RFC7761] is the current specification of the Protocol Independent
   Multicast - Sparse Mode (PIM-SM) for IPv4 and IPv6 networks.  A
   conforming implementation of PIM-SM elects a Designated Router (DR)
   on each PIM-SM interface.  When a group of PIM-SM nodes is connected
   to a shared-media shared media segment, e.g., Ethernet, the node elected as DR is
   to act on behalf of directly connected hosts in the context of the
   PIM-SM protocol.  Failure of the DR impacts the quality of the
   multicast services it provides to directly connected hosts because
   the default failure detection interval for PIM-SM routers is 105
   seconds.  Introduction of Backup DR (BDR)
   ([I-D.ietf-pim-dr-improvement]) improves convergence time in PIM-SM
   over shared-media segment but still depends on a long failure
   detection interval.

   Bidirectional Forwarding Detection (BFD) [RFC5880] had been
   originally defined to detect a failure of point-to-point (p2p) paths
   - single-hop [RFC5881], multihop [RFC5883].  In some PIM-SM
   deployments, a p2p BFD can be used to detect a failure and enable faster conversion.
   failover.  [RFC8562] extends the BFD base specification [RFC5880] for
   multipoint and multicast networks precisely characterizes deployment
   scenarios for PIM-SM over a LAN segment.  Among specific
   characteristics of p2mp BFD that particularly benefit PIM-SM over a
   LAN segment is a faster transition to the Up state of the p2mp BFD
   session due to avoidance of the three-way handshake required in p2p
   BFD [RFC5880].  Also, because the router that transmits BFD Control
   messages uses the BFD Demand mode [RFC5880], it maintains less BFD
   state comparing to than the Asynchronous mode.  Point-
   to-multipoint  Point-to-multipoint (p2mp) BFD can
   enable faster detection of PIM-SM router failure and thus minimize
   multicast service disruption.  The monitored PIM-SM router acts as
   the head and other routers as tails of a p2mp BFD session.  This
   document defines the monitoring of PIM-
   SM DR and BDR a PIM-SM router using p2mp BFD.  Other cases of using p2mp BFD in PIM-
   SM are outside the scope of this specification.
   The document also defines the extension to PIM-SM [RFC7761] to
   bootstrap a PIM-SM router to join in p2mp BFD session over shared-media link. shared
   media segment.

1.1.  Conventions used in this document

1.1.1.  Terminology

   This document uses terminology defined in [RFC5880], [RFC8562], and
   [RFC7761]. familiarity with these specifications and the terminology
   used is expected.

1.1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  BFD Discriminator PIM Hello Option

   Figure 1 displays the new optional BFD Discriminator PIM Hello option
   to bootstrap a tail of the p2mp BFD session.

        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
       |          OptionType           |         OptionLength          |
       |                       My  Discriminator                       |

                Figure 1: BFD Discriminator PIM Hello Option

   where new fields are interpreted as:

      OptionType: TBA.

      OptionLength: MUST be set to 4.

      My Discriminator: My Discriminator ([RFC5880]) value allocated by
      the head.

   If the value of the OptionLength field is not equal to 4, the BFD
   Discriminator PIM Hello option is considered malformed, and the
   receiver MUST stop processing PIM Hello options.  If the value of the
   My Discriminator field equals zero, then the BFD Discriminator PIM
   Hello option MUST be considered invalid, and the receiver MUST ignore
   it.  The receiver SHOULD log the a notification regarding the malformed
   or invalid BFD Discriminator Hello option under the control of a
   throttling logging mechanism.

2.1.  Using P2MP BFD in PIM DR/BDR Router Monitoring

   The head MUST create a BFD session of type MultipointHead [RFC8562].
   Note that any PIM-SM router, regardless of its role, MAY become a
   head of a p2mp BFD session.  To control the volume of BFD control
   traffic on a shared media segment, an operator should carefully
   select PIM-SM routers configured as a head of a p2mp BFD session.
   The head MUST include the BFD Discriminator option in its Hello

   If a PIM-SM router is configured to monitor the head by using p2mp
   BFD, referred to through this document as 'tail', receives PIM-Hello a PIM-
   Hello packet with the BFD Discriminator PIM Hello option, the tail
   MAY create a p2mp BFD session of type MultipointTail, as defined in

   The node that includes the BFD Discriminator PIM Hello option
   transmits BFD Control packets periodically.  For the tail to
   correctly demultiplex BFD [RFC8562], the source address, and My
   Discriminator values of the BFD packets MUST be the same as those
   used in the PIM Hello message.  If that is not the case, the tail BFD
   node would not be able to monitor the state of the PIM-SM node, that
   is, the head of the p2mp BFD session, though the regular PIM-SM
   mechanisms remain fully operational.

   If the tail detects a MultipointHead failure [RFC8562], it MUST
   delete the corresponding neighbor state.  If the failed head was the
   DR (or BDR), the DR (or BDR) election mechanism state and follow procedures defined
   in [RFC7761] or
   [I-D.ietf-pim-dr-improvement] is followed. [RFC7761].

   If the head ceases to include the BFD Discriminator PIM Hello option
   in its PIM-Hello message, tails MUST close the corresponding
   MultipointTail BFD session. session without affecting the PIM state in any
   way.  Thus the tail stops using BFD to monitor the head and reverts
   to the procedures defined in [RFC7761] and
   [I-D.ietf-pim-dr-improvement]. [RFC7761].

2.2.  P2MP BFD in PIM DR Load Balancing

   [RFC8775] specifies the PIM Designated Router Load Balancing (DRLB)
   functionality.  Any PIM router that advertises the DRLB-Cap Hello
   Option can become the head of a p2mp BFD session, as specified in
   Section 2.1.  The head router administratively sets the
   bfd.SessionState to Up in the MultipointHead session [RFC8562] only
   if it is a Group Designated Router (GDR) Candidate, as specified in
   Sections 5.5 and 5.6 of [RFC8775].  If the router is no longer the
   GDR, then it MUST shut down following the procedures described in
   Section 5.9 [RFC8562].  For each GDR Candidate that includes BFD
   Discriminator option in its PIM Hello, the PIM DR creates a
   MultipointTail session [RFC8562].  PIM DR demultiplexes BFD sessions
   based on the value of the My Discriminator field and the source IP
   address.  If PIM DR detects a failure of one of the sessions, it MUST
   remove that router from the GDR Candidate list and immediately
   transmit a new DRLB-List option.

2.3.  Multipoint BFD Encapsulation

   The MultipointHead of a p2mp BFD session when transmitting BFD
   Control packet:

      MUST packets:

      must set TTL or Hop Limit value to 255 (Section 5 [RFC5881]);

      MUST use the group address ALL-PIM-ROUTERS ('' for IPv4
      and 'ff02::d' for IPv6) as destination IP address

3.  IANA Considerations

   IANA is requested to allocate a new OptionType value from PIM-Hello
   Options registry according to:


       | Value Name | Length Number | Name Protocol                     | Reference     |
       | TBA   | 4      | BFD Discriminator Option | This document |
   |             |                | Option            |               |

                   Table 1: BFD Discriminator option type

4.  Security Considerations

   The security considerations discussed in [RFC7761], [RFC5880],
   [RFC8562], [RFC8775], and [I-D.ietf-pim-dr-improvement] [RFC8775] apply to this document.

   An implementation that supports this specification SHOULD use a
   mechanism to control the maximum number of BFD sessions that can be
   active at the same time.

5.  Acknowledgments

   The authors cannot say enough to express their appreciation of the
   comments and suggestions we received from Stig Venaas.  The authors
   greatly appreciate the comments and suggestions by Alvaro Retana that
   improved the clarity of the document.

6.  References

6.1.  Normative References

              Zhang, Z., Hu, F., Xu, B., and M. Mishra, "Protocol
              Independent Multicast - Sparse Mode (PIM-SM) Designated
              Router (DR) Improvement", Work in Progress, Internet-
              Draft, draft-ietf-pim-dr-improvement-11, 17 February 2021,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

   [RFC8775]  Cai, Y., Ou, H., Vallepalli, S., Mishra, M., Venaas, S.,
              and A. Green, "PIM Designated Router Load Balancing",
              RFC 8775, DOI 10.17487/RFC8775, April 2020,

6.2.  Informative References

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,

   [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>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com

   Ji Xiaoli
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District

   Email: ji.xiaoli@zte.com.cn