Internet-Draft | Applicability of BFD P2MP in VRRP | October 2023 |
Mirsky, et al. | Expires 13 April 2024 | [Page] |
This document discusses the applicability of Bidirectional Forwarding Detection (BFD) for multipoint networks to provide Virtual Router Redundancy Protocol (VRRP) with sub-second convergence of the Active router and defines the extension to bootstrap point-to-multipoint BFD session.¶
This draft updates RFC 5798.¶
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The [RFC5798] is the current specification of the Virtual Router Redundancy Protocol (VRRP) for IPv4 and IPv6 networks. [I-D.ietf-rtgwg-vrrp-rfc5798bis] is intended to obsolete [RFC5798] and its terminology is already used in this document. VRRPv3 allows for a faster switchover to a Backup router. Using such capability with the software-based implementation of VRRP may prove challenging. But it still may be possible to deploy VRRP and provide sub-second detection of Active router failure by Backup routers.¶
Bidirectional Forwarding Detection (BFD) [RFC5880] had been originally defined detect failure of point-to-point (p2p) paths: single-hop [RFC5881], multihop [RFC5883]. Single-hop BFD may be used to enable Backup routers to detect a failure of the Active router within 100 msec or faster.¶
[RFC8562] extends [RFC5880] for multipoint and multicast networks, which matches the deployment scenarios for VRRP over the LAN segment. This document demonstrates how point-to-multipoint (p2mp) BFD can enable faster detection of the Active router failure and thus minimize service disruption in a VRRP domain. The document also defines the extension to VRRP [RFC5798] to bootstrap a VRRP Backup router to join in a p2mp BFD session.¶
BFD: Bidirectional Forwarding Detection¶
p2mp: Pont-to-Multipoint¶
VRRP: Virtual Router Redundancy Protocol¶
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.¶
A router may be part of several Virtual Router Redundancy groups, as Active in some and as Backup in others. Supporting sub-second mode for VRRPv3 [RFC5798] for all these roles without specialized support in the data plane may prove challenging. BFD already has many implementations based on HW that are capable of supporting multiple sub-second sessions concurrently.¶
[RFC8562] may provide an efficient and scalable solution for fast-converging environment that uses the default route rather than dynamic routing. Each redundancy group presents itself as a p2mp BFD session, with its Active router being the root and Backup routers being the tails of the p2mp BFD session. Figure 1 displays the extension of VRRP [RFC5798] 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Type | Virtual Rtr ID| Priority |Count IPvX Addr| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Rsvd |B| Max Adver Int | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | IPvX Address(es) | + + + + + + + + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Active Router Discriminator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The new fields are interpreted as follows:¶
The Active router, configured to use p2mp BFD to support faster convergence of VRRP, starts transmitting BFD control packets with VRID as a source IP address and the locally allocated value as the value of the My Discriminator field ([RFC5880]). The same non-zero value of My Discriminator MUST be set as the value of the Active Router Discriminator field. The BFD flag MUST be set in the VRRP packet. A Backup router demultiplexes p2mp BFD test sessions based on VRID that it has been configured with and the non-zero My Discriminator value it learns from the received VRRP packet. When a Backup router detects the failure of the Active router, it re-evaluates its role in the VRID. As a result, the Backup router may become the Active router of the given VRID or continue as a Backup router. If the former is the case, then the new Active router MUST select My Discriminator and start transmitting p2mp BFD control packets using Active router IP address as the source IP address for p2mp BFD control packets. If the latter is the case, then the Backup router MUST wait for the VRRP packet from the new VRRP Active router that will bootstrap the new p2mp BFD session.¶
The MultipointHead of p2mp BFD session when transmitting BFD control packet:¶
This document makes no requests for IANA allocations. This section may be deleted by RFC Editor.¶
This document defines an alternative way, to the one defined in [RFC5798], to accelerate detecting a failure that affects VRRP functionality using p2mp BFD. The operation of either protocol is not changed.¶
Security considerations discussed in [RFC5798], [RFC5880], [RFC5881], and [RFC8562], apply to this document.¶