RFC 9186: Fast Failover in Protocol Independent Multicast - Sparse Mode (PIM-SM) Using Bidirectional Forwarding Detection (BFD) for Multipoint Networks

Status of This Memo

This is an Internet Standards Track document.¶

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9186.¶

Copyright Notice

Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶

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1. Introduction

Faster convergence in the control plane minimizes the periods of traffic loss due to the use of stale routing information, transient routing loops, and other situations that may negatively affect service data flow. Faster convergence in the control plane is beneficial 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. 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 segment, e.g., Ethernet, the node elected as the DR acts 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.¶

Bidirectional Forwarding Detection (BFD) [RFC5880] was originally defined to detect a failure of a point-to-point (P2P) path, single hop [RFC5881], or multihop [RFC5883]. In some PIM-SM deployments, a P2P BFD can be used to detect a failure and enable faster failover. [RFC8562] extends the BFD base specification [RFC5880] for multipoint and multicast networks, which matches the deployment scenarios for PIM-SM over a LAN segment. A BFD system in a point-to-multipoint (P2MP) environment that transmits BFD Control messages using the BFD Demand mode [RFC5880] creates less BFD state than the Asynchronous mode. P2MP BFD can enable faster detection of PIM-SM router failure compared to PIM-SM without BFD and thus minimizes multicast service disruption. The monitored PIM-SM router acts as the head and other routers act as tails of a P2MP BFD session. This document defines the monitoring of a PIM-SM router using P2MP BFD. This document also defines the extension to PIM-SM [RFC7761] to bootstrap a PIM-SM router to join in the P2MP BFD session over a shared media segment.¶

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          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       HeadDiscriminator                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where new fields are interpreted as:¶

OptionType:

39¶

OptionLength:

MUST be set to 4.¶

HeadDiscriminator:

the 4-octet field MUST be included in the BFD Discriminator PIM-SM Hello Option. The value MUST NOT be zero. It equals the value of My Discriminator [RFC5880] 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 HeadDiscriminator field equals zero, then the BFD Discriminator PIM Hello Option MUST be considered invalid, and the receiver MUST ignore it. The receiver SHOULD log a notification regarding the malformed or invalid BFD Discriminator Hello Option under the control of a throttling logging mechanism.¶

3. IANA Considerations

IANA has allocated a new OptionType value in the "PIM-Hello Options" registry according to Table 1:¶

4. Security Considerations

This document defines a way to accelerate detection of a failure that affects PIM functionality by using BFD. The operation of either protocol is not changed.¶

The security considerations discussed in [RFC5880], [RFC5881], [RFC7761], [RFC8562], and [RFC8775] apply to this document.¶

Authors' Addresses