Hi Emmanuel,
thank you for your thorough review and thoughtful suggestions. Please find
my notes below tagged by GIM>>. Attached, please find the new working
version of the draft.
Regards,
Greg
On Wed, Mar 13, 2024 at 12:46 AM Emmanuel Baccelli via Datatracker <
[email protected]> wrote:
> Reviewer: Emmanuel Baccelli
> Review result: Has Nits
>
> Hello,
>
> I've been selected as Routing Directorate (early) reviewer for this draft.
>
> I have a few nits (nothing major) and a couple of suggestions.
>
> Some of my comments might come through as pedantic -- mostly due to my
> superficial prior knowledge concerning VRRP!
>
> # Abstract:
>
> suggested change/clarification
> "...sub-second convergence of the Active router and..."
> => "...sub-second convergence for the process determining the Active router
> and..." or something equivalent.
>
GIM>> Thank you for your suggestion. Accepted.
>
> # Section 1:
>
> suggested change/clarification
> "this document demonstrates how... can enable faster detection..."
> => "this document specifies fast transition to a new Active router, upon
> detection of..." or something equivalent.
>
GIM>> VRRPv3 allows for sub-second switchover to a new Active router
although using high-rate protocol's Hello. This proposal describes an
alternative mechanism, i.e., p2mp BFD, to support that functionality. It
seems like the innovation the draft provides is in the way to support the
essential functionality using a light-weight BFD mechansim. Perhpas the
current wording is acceptable.
>
> # Section 2:
>
> "Supporting sub-second mode... in the data plane may prove challenging"
> => Would be best to hint at the main reason why (costs in terms of control
> traffic overhead?).
>
GIM>> Clarified with the following update:
NEW TEXT:
Supporting sub-second mode
for VRRPv3 [I-D.ietf-rtgwg-vrrp-rfc5798bis] for all these roles
without specialized support in the data plane may prove challenging
because of the increased load on the control plane.
>
> "BFD already has many implementationq based on HW"
> => Cite at least one implementation, if possible?
>
GIM>> By now BFD, to the best of my understanding, supported by all HW
platforms. Naming one and not mention others seems like undesirable and
devisive. WDYT?
>
> # Section 3:
>
> My Discriminator => cite RFC5880 upon first use of this term in the doc ;)
>
GIM>> Thanks! Added.
>
> "... starts transmitting BFD control packets with VRID as a source IP
> address
> and ..." => it is unclear how VRID (1 Byte) can be used as IP address. Can
> you
> rephrase/clarify?
>
GIM>> You're correct. Based on the comments by Joe Clarke
<https://mailarchive.ietf.org/arch/msg/rtgwg/Wd7agbSfnSIxfjs_jSkNWt6ZjMQ/>,
the new -08 version is as follows:
The Active router, configured to use p2mp BFD to support faster
convergence of VRRP, starts transmitting BFD control packets with
IPvX address associated with the Virtual Router
[I-D.ietf-rtgwg-vrrp-rfc5798bis] as a source IP address and the
locally allocated value as the value of the My Discriminator field
([RFC5880]).
WDYT?
>
> "... when a backup router detects failure of the Active router, ..."
> => using which mechanism/RFC ? I suggest citing it explicitly
>
GIM>> Added reference to Section 5.11 RFC 8562 that defines how detection
time is calculated for the MultipointTail in p2mp BFD session.
>
> "... it reevaluates its role as VRID."
> => it is unclear how this happens exactly. If this is intentionally left
> unspecified as implementation-dependent, I suggest to say it explicitly in
> the
> doc.
>
GIM>> That passage was also changed as a result of addressing comments from
Joe Clarke. I hope that the new text is clearer:
... it re-evaluates its role in the Virtual Router.
> "... the new Active router MUST select My Discriminator and..."
> => it is unclear which discriminator is meant here. Do you mean the value
> locally allocated (as it was still Backup router)?
>
GIM>> Thank you for pointing it out to me. It is unclear. I propose the
following update:
NEW TEXT:
As a result, the Backup router may become the Active router
of the given Virtual Router or continue as a Backup router. If the
former is the case, then the new Active router MUST select its new My
Discriminator value, include that value in the VRRP packet to
bootstrap a new p2mp BFD session, and start transmitting p2mp BFD
control packets using the Active router IP address as the source IP
address for p2mp BFD control packets and its new My Discriminator
value.
Is it clearer now?
> # Section 5:
>
> "... to accelerate detecting a failure that affects VRRP"
> => it is unclear what in the doc accelerates *detecting* a failure. I
> suggest a
> rephrase such as "...to accelerate transition to a new Active router upon
> detection of BFD failure" or something equivalent.
>
GIM>> I think that the switchover, after the detection of the network
failure, is implementation-dependent. The document is aimed to describe
"an alternative way, to the one defined in
[I-D.ietf-rtgwg-vrrp-rfc5798bis], to accelerate detecting a failure
that affects VRRP functionality using p2mp BFD. The operation of
either protocol is not changed."
RTGWG G. Mirsky
Internet-Draft Ericsson
Updates: 5798bis (if approved) J. Tantsura
Intended status: Standards Track NVIDIA
Expires: 23 September 2024 G. Mishra
Verizon Inc.
22 March 2024
Applicability of Bidirectional Forwarding Detection (BFD) for Multi-
point Networks in Virtual Router Redundancy Protocol (VRRP)
draft-ietf-rtgwg-vrrp-p2mp-bfd-09
Abstract
This document discusses the applicability of Bidirectional Forwarding
Detection (BFD) for multipoint networks to provide Virtual Router
Redundancy Protocol with sub-second convergence for the process
determining the Active router and defines the extension to bootstrap
point-to-multipoint BFD session.
This draft updates RFC 5798bis [Ed.Note: When the RFC 5798bis is
published, change to the assigned new number].
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (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 include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised 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 . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The [I-D.ietf-rtgwg-vrrp-rfc5798bis] 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 Active router failure by Backup
routers.
Bidirectional Forwarding Detection (BFD) [RFC5880] had been
originally defined to 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 [I-D.ietf-rtgwg-vrrp-rfc5798bis] to
bootstrap a VRRP Backup router to join in a 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
Active in some and as Backup in others. Supporting sub-second mode
for VRRPv3 [I-D.ietf-rtgwg-vrrp-rfc5798bis] for all these roles
without specialized support in the data plane may prove challenging
because of the increased load on the control plane. 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 Active router being the root and Backup routers
being the tails of the p2mp BFD session. Figure 1 displays the
extension of VRRP [I-D.ietf-rtgwg-vrrp-rfc5798bis] 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) |
+ +
+ +
+ +
+ +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Active Router 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 Active Router
Discriminator field is appended to VRRP packet defined in
[I-D.ietf-rtgwg-vrrp-rfc5798bis];
Active Router Discriminator - the four-octet field. The value
MUST NOT be zero, and it equals the My Discriminator [RFC5880]
value allocated by the root of the p2mp BFD session.
The Active router, configured to use p2mp BFD to support faster
convergence of VRRP, starts transmitting BFD control packets with
IPvX address associated with the Virtual Router
[I-D.ietf-rtgwg-vrrp-rfc5798bis] 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 IPvX address associated with the Virtual
Router 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, according to
the Section 5.11 [RFC8562], it re-evaluates its role in the Virtual
Router. As a result, the Backup router may become the Active router
of the given Virtual Router or continue as a Backup router. If the
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former is the case, then the new Active router MUST select its new My
Discriminator value, include that value in the VRRP packet to
bootstrap a new p2mp BFD session, and start transmitting p2mp BFD
control packets using the Active router IP address as the source IP
address for p2mp BFD control packets and its new My Discriminator
value. If the latter is the case, the Backup router MUST wait for
the VRRP packet from the new VRRP Active 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 Active router 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
[I-D.ietf-rtgwg-vrrp-rfc5798bis], to accelerate detecting a failure
that affects VRRP functionality using p2mp BFD. The operation of
either protocol is not changed.
Security considerations discussed in
[I-D.ietf-rtgwg-vrrp-rfc5798bis], [RFC5880], [RFC5881], and
[RFC8562], apply to this document.
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6. Acknowledgements
7. Normative References
[I-D.ietf-rtgwg-vrrp-rfc5798bis]
Lindem, A. and A. Dogra, "Virtual Router Redundancy
Protocol (VRRP) Version 3 for IPv4 and IPv6", Work in
Progress, Internet-Draft, draft-ietf-rtgwg-vrrp-
rfc5798bis-18, 4 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
vrrp-rfc5798bis-18>.
[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>.
[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: [email protected]
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Jeff Tantsura
NVIDIA
Email: [email protected]
Gyan Mishra
Verizon Inc.
Email: [email protected]
Mirsky, et al. Expires 23 September 2024 [Page 7]
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