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Versions: (draft-mirsky-pim-bfd-p2mp-use-case) 00 01 02

PIM Working Group                                              G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                               J. Xiaoli
Expires: January 26, 2020                                ZTE Corporation
                                                           July 25, 2019


 Bidirectional Forwarding Detection (BFD) for Multi-point Networks and
     Protocol Independent Multicast - Sparse Mode (PIM-SM) Use Case
                  draft-ietf-pim-bfd-p2mp-use-case-02

Abstract

   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

   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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   This Internet-Draft will expire on January 26, 2020.

Copyright Notice

   Copyright (c) 2019 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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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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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 . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Applicability of p2mp BFD . . . . . . . . . . . . . . . . . .   3
     3.1.  Multipoint BFD Encapsulation  . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   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
   protocols.

   [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
   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



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   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

   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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.

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 TLV to bootstrap tail of the p2mp BFD session.









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        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 TLV to Bootstrap P2MP BFD session

   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.

   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
   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



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   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].

3.1.  Multipoint BFD Encapsulation

   The MultipointHead of p2mp BFD session when transmitting BFD control
   packet:

      MUST set TTL value to 1;

      SHOULD use group address ALL-PIM-ROUTERS ('224.0.0.13' 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







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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.

7.  Normative References

   [I-D.ietf-pim-dr-improvement]
              Zhang, Z., hu, f., Xu, B., and m. mishra, "PIM DR
              Improvement", draft-ietf-pim-dr-improvement-07 (work in
              progress), January 2019.

   [I-D.mankamana-pim-bdr]
              mishra, m., "PIM Backup Designated Router Procedure",
              draft-mankamana-pim-bdr-02 (work in progress), April 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

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



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   [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>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


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

   Email: ji.xiaoli@zte.com.cn



























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