PIM Working Group                                              G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                               J. Xiaoli
Expires: January 26, 2021                                ZTE Corporation
                                                           July 25, 2020

 Bidirectional Forwarding Detection (BFD) for Multi-point Networks and
     Protocol Independent Multicast - Sparse Mode (PIM-SM) Use Case


   This document discusses the use of Bidirectional Forwarding Detection
   (BFD) for multi-point networks to provide nodes that participate in
   Protocol Independent Multicast - Sparse Mode (PIM-SM) with the sub-
   second convergence.  Optional extension to PIM-SM Hello, as specified
   in RFC 7761, to bootstrap point-to-multipoint BFD session. also
   defined in this document.

Status of This Memo

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   This Internet-Draft will expire on January 26, 2021.

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   include Simplified BSD License text as described in Section 4.e of
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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.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Applicability of p2mp BFD . . . . . . . . . . . . . . . . . .   4
     3.1.  Using P2MP BFD in PIM DR/BDR Monitoring . . . . . . . . .   4
     3.2.  P2MP BFD in PIM DR Load Balancing . . . . . . . . . . . .   5
     3.3.  Multipoint BFD Encapsulation  . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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.
   Confirming implementation of PIM-SM elects a Designated Router (DR)
   on each PIM-SM interface.  When a group of PIM-SM nodes is connected
   to shared-media segment, e.g., Ethernet, the one 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), proposed in
   [I-D.ietf-pim-dr-improvement], improves convergence time in the PIM-
   SM over shared-media segment but still depends on long failure
   detection interval.

   Bidirectional Forwarding Detection (BFD) [RFC5880] had been
   originally defined to detect failure of point-to-point (p2p) paths -
   single-hop [RFC5881], multihop [RFC5883].  [RFC8562] extends the BFD

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   base specification [RFC5880] for multipoint and multicast networks,
   which precisely characterizes deployment scenarios for PIM-SM over
   LAN segment.  This document demonstrates how point-to-multipoint
   (p2mp) BFD can enable faster detection of PIM-SM router failure and
   thus minimize multicast service disruption.  The document also
   defines the extension to PIM-SM [RFC7761] and
   [I-D.ietf-pim-dr-improvement] to bootstrap a PIM-SM router to join in
   p2mp BFD session over shared-media link.

1.1.  Conventions used in this document

1.1.1.  Terminology

   BFD: Bidirectional Forwarding Detection

   BDR: Backup Designated Router

   DR: Designated Router

   DRLB: Designated Router Load Balancing

   DRLB-Cap: DRLB Capability Hello Option

   DRLB-List: DRLB List Hello Option

   GDR: Group Designated Router

   p2mp: Pont-to-Multipoint

   PIM-SM: Protocol Independent Multicast - Sparse Mode

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.  Problem Statement

   [RFC7761] does not provide a method for fast, e.g., sub-second,
   failure detection of a neighbor PIM-SM router.  BFD already has many
   implementations based on HW that are capable of supporting multiple
   sub-second sessions concurrently.

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3.  Applicability of p2mp BFD

   [RFC8562] may provide an efficient and scalable solution for the
   fast-converging environment that demonstrates the head-tails
   relationship.  Each such group presents itself as p2mp BFD session
   with its head being the root and other routers being tails of the
   p2mp BFD session.  Figure 1 displays the new optional BFD
   Discriminator PIM Hello Option to bootstrap tail of the p2mp BFD

        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 is a value (TBA1) assigned by IANA Section 4 that
      identifies the TLV as BFD Discriminator TLV;

      OptionLength value is always 4

      My Discriminator - My Discriminator value allocated by the root of
      the p2mp BFD session.

3.1.  Using P2MP BFD in PIM DR/BDR Monitoring

   If PIM-SM routers that support this specification are configured to
   use p2mp BFD for faster convergence, then the router to be monitored,
   referred to as 'head', MUST create BFD session of type
   MultipointHead, as defined in [RFC8562].  If the head doesn't support
   [I-D.ietf-pim-dr-improvement], but, for example, uses procedures
   defined in [I-D.mankamana-pim-bdr], then it MUST include BFD TLV in
   its PIM-Hello message.  If the head uses extensions defined in
   [I-D.ietf-pim-dr-improvement], then DR MUST include BFD TLV in its
   Hello message.  The DR Address TLV also MUST be included in the Hello
   message.  For a BDR it is RECOMMENDED to include BFD TLV in its Hello
   message.  If BDR includes BFD TLV, then the BDR Address TLV also MUST
   be present in the Hello message.  Then the head MUST begin periodic
   transmission of BFD control packets.  Source IP address of the BFD
   control packet MUST be the same as the source IP address of the PIM-
   Hello with BFD TLV messages being transmitted by the head.  The
   values of My Discriminator in the BFD control packet and My

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   Discriminator field of the BFD TLV in PIM-Hello, transmitted by the
   head MUST be the same.  When a PIM-SM router is configured to monitor
   the head by using p2p BFD, referred to through this document as
   'tail', receives PIM-Hello packet with BFD TLV it MAY create p2mp BFD
   session of type MultipointTail, as defined in [RFC8562].

   Because p2mp BFD doesn't use the three-way handshake and the head
   transmits BFD control packets with the value of Your Discriminator
   field set to zero, [RFC8562] modified how a BFD system demultiplexes
   received BFD control packet.  The tail demultiplexes p2mp BFD test
   session based on head's source IP address, the My Discriminator value
   it learned from BFD Discriminator TLV and the identity of the
   multipoint path that the BFD control packet was received from.  The
   Detection Time for p2mp BFD sessions is defined differently from the
   definition provided in [RFC5880].  The Detection Time for each
   MultipointTail session is calculated as the product of the last
   received values of Desired Min TX Interval and Detect Mult.  A tail
   declares the BFD session down after the Detection Timer expires.  If
   the tail has detected MultipointHead failure, it MUST remove the
   neighbor.  If the failed head node was PIM-SM DR or BDR, the tail MAY
   start DR Election process as specified in Section 4.3.2 [RFC7761] or
   Section 4.1 [I-D.ietf-pim-dr-improvement] respectively.

   If the head ceased to include BFD TLV in its PIM-Hello message, tails
   MUST close the corresponding MultipointTail BFD session.  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].

3.2.  P2MP BFD in PIM DR Load Balancing

   [RFC8775] defined the modification, Designated Router Load Balancing
   (DRLB), to the PIM-SM protocol that allows for distribution of PIM-SM
   DR responsibilities on a multi-access network segment.  [RFC8775]
   introduced the new PIM Hello options - Load Balancing Capability
   (DRLB-Cap) and DR Load Balancing List (DRLB-List).  PIM router that
   includes DRLB-Cap Hello Option MAY include BFD Discriminator PIM
   Hello Option (Figure 1).  That router MUST create a BFD session and
   set itself as MultipointHead [RFC8562].  The router MUST set
   bfd.SessionState in the MultipointHead session to Down.  If a PIM
   router that includes BFD Discriminator Option in its Hello finds its
   address in DRLB-List PIM Hello Option as Group Designated Router
   (GDR) Candidate for the first time, the router MUST set
   bfd.SessionState to Up and start periodically transmit BFD control
   messages.  If the PIM router that was GDR Candidate doesn't find its
   address in the most recent DRLB-List Option, the router MUST set
   bfd.SessionState to Down and cease transmitting BFD control messages.
   For each GDR Candidate that includes BFD Discriminator Option in its
   PIM Hello, PIM DR creates a MultipointTail session [RFC8562].  PIM DR

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   demultiplexes BFD sessions based on the value in 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.

3.3.  Multipoint BFD Encapsulation

   The MultipointHead of p2mp BFD session when transmitting BFD control

      MUST set TTL value to 1;

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

      MAY use network broadcast address for IPv4 or link-local all nodes
      multicast group for IPv6 as the destination IP address;

      MUST set destination UDP port value to 3784 when transmitting BFD
      control packets, as defined in [RFC8562].

4.  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 | This document |

                  Table 1: BFD Discriminator option type

5.  Security Considerations

   Security considerations discussed in [RFC7761], [RFC5880], and
   [RFC8562], and [I-D.ietf-pim-dr-improvement] 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.

6.  Acknowledgments

   Authors cannot say enough to express their appreciation of comments
   and suggestions we received from Stig Venaas.

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7.  References

7.1.  Normative References

              Zhang, Z., hu, f., Xu, B., and m. mishra, "PIM DR
              Improvement", draft-ietf-pim-dr-improvement-09 (work in
              progress), October 2019.

   [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,

   [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>.

   [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,

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7.2.  Informative References

              mishra, m., Goh, J., and G. Mishra, "PIM Backup Designated
              Router Procedure", draft-mankamana-pim-bdr-04 (work in
              progress), April 2020.

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

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