Internet DRAFT - draft-mtm-rtgwg-vrrp-p2mp-bfd
draft-mtm-rtgwg-vrrp-p2mp-bfd
BFD Working Group G. Mirsky
Internet-Draft Ericsson
Updates: 5798 (if approved) J. Tantsura
Intended status: Standards Track Microsoft
Expires: 5 June 2022 G. Mishra
Verizon Inc.
2 December 2021
Applicability of Bidirectional Forwarding Detection (BFD) for Multi-
point Networks in Virtual Router Redundancy Protocol (VRRP)
draft-mtm-rtgwg-vrrp-p2mp-bfd-01
Abstract
This document discusses the applicability of Bidirectional Forwarding
Detection (BFD) for multipoint networks to provide Virtual Router
Redundancy Protocol (VRRP) with sub-second Master convergence and
defines the extension to bootstrap point-to-multipoint BFD session.
This draft updates RFC 5798.
Status of This Memo
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Please review these documents carefully, as they describe your rights
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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 . . . . . . . . . . . . . . . . . . 3
3.1. Multipoint BFD Encapsulation . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The [RFC5798] is the current specification of the Virtual Router
Redundancy Protocol (VRRP) for IPv4 and IPv6 networks. 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 Master 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 Master 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 Master 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 p2mp
BFD session.
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1.1. Conventions used in this document
1.1.1. Terminology
BFD: Bidirectional Forwarding Detection
p2mp: Pont-to-Multipoint
VRRP: Virtual Router Redundancy Protocol
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
A router may be part of several Virtual Router Redundancy groups, as
Master 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.
3. Applicability of p2mp BFD
[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 Master 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.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Type | Virtual Rtr ID| Priority |Count IPvX Addr|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Rsvd |B| Max Adver Int | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| IPvX Address(es) |
+ +
+ +
+ +
+ +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Master Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: VRRP Extension to Bootstrap P2MP BFD session
The new fields are interpreted as follows:
B(FD) - a one-bit flag that indicates that the Master
Discriminator field is appended to VRRP packet defined in
[RFC5798];
Master Discriminator - the four-octet field. The value MUST NOT
be zero, and it equals the My Discriminator value allocated by the
root of the p2mp BFD session.
The Master 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 Master
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 Master router, it re-evaluates its role in
the VRID. As a result, the Backup router may become the Master
router of the given VRID or continue as a Backup router. If the
former is the case, then the new Master router MUST select My
Discriminator and start transmitting p2mp BFD control packets using
Master IP address as the source IP address for p2mp BFD control
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packets. If the latter is the case, then the Backup router MUST wait
for the VRRP packet from the new VRRP Master router that will
bootstrap the new p2mp BFD session.
3.1. Multipoint BFD Encapsulation
The MultipointHead of p2mp BFD session when transmitting BFD control
packet:
MUST set TTL or Hop Limit value to 255 (Section 5 [RFC5881]).
Similarly, all received BFD Control packets that are demultiplexed
to the session MUST be discarded if the received TTL or Hop Limit
is not equal to 255;
SHOULD use group address VRRP ('224.0.0.18' for IPv4 and
'FF02:0:0:0:0:0:0:12' for IPv6) as destination IP address
MAY use network broadcast address for IPv4 or link-local all nodes
multicast group for IPv6 as destination IP address;
MUST set destination UDP port value to 3784 when transmitting BFD
control packets, as defined in [RFC8562];
MUST use the Master IP address as the source IP address.
4. IANA Considerations
This document makes no requests for IANA allocations. This section
may be deleted by RFC Editor.
5. Security Considerations
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.
6. Acknowledgements
7. Normative References
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[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>.
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010,
<https://www.rfc-editor.org/info/rfc5798>.
[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>.
[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
Ericsson
Email: gregimirsky@gmail.com
Jeff Tantsura
Microsoft
Email: jefftant.ietf@gmail.com
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Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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