Internet DRAFT - draft-ietf-pim-bdr
draft-ietf-pim-bdr
Network Working Group M. Mishra
Internet-Draft S. Santhanam
Intended status: Informational A. Paramasivam
Expires: September 8, 2022 Cisco Systems
I. Romdhani
Edinburgh Napier University
G. Mishra
Verizon Communications Inc. (VZ)
March 7, 2022
PIM Backup Designated Router Procedure
draft-ietf-pim-bdr-01
Abstract
On a multi-access network, one of the PIM routers is elected as a
Designated Router (DR). On the last hop LAN, the PIM DR is
responsible for tracking local multicast listeners and forwarding
traffic to these listeners if the group is operating in PIM-SM. In
this document, we propose a mechanism to elect backup DR on a shared
LAN. A backup DR on LAN would be useful for faster convergence.
This draft introduces the concept of a Backup Designated Router (BDR)
and the procedure to implement it.
Status of This Memo
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This Internet-Draft will expire on September 8, 2022.
Copyright Notice
Copyright (c) 2022 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability and deviation from draft PIM DR Improvement . . 4
4. Protocol Specification . . . . . . . . . . . . . . . . . . . 4
4.1. PIM Backup DR (BDR) election procedure . . . . . . . . . 4
4.2. Existing PIM DR failure . . . . . . . . . . . . . . . . . 4
4.3. Existing PIM BDR failure . . . . . . . . . . . . . . . . 4
4.4. New PIM Router addition in network . . . . . . . . . . . 4
4.4.1. New PIM router eligible to be PIM DR on shared LAN . 4
4.4.2. New PIM router eligible to be PIM BDR on shared LAN . 5
4.4.3. New PIM router is not eligible to be PIM DR or BDR on
shared LAN . . . . . . . . . . . . . . . . . . . . . 5
4.5. Initial case, All new PIM router coming up in shared LAN 5
4.6. Benefit . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Manageability Considerations . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6
10. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
On a multi-access LAN such as an Ethernet, one of the PIM routers is
elected as a DR. The PIM DR has two roles in the PIM-SM protocol.
On the first hop network, the PIM DR is responsible for registering
an active source with the Rendezvous Point (RP) if the group is
operating in PIM-SM. On the last hop LAN, the PIM DR is responsible
for tracking local multicast listeners and forwarding to these
listeners if the group is operating in PIM-SM.
Consider the following last hop LAN in Figure 1:
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( core networks )
| | |
| | |
R1 R2 R3
| | |
--(last hop LAN)--
|
|
(many receivers)
Figure 1: Last Hop LAN
Assume R1 is elected as the Designated Router. According to
[RFC4601], R1 will be responsible for forwarding traffic to that LAN
on behalf of any local member. In addition to keeping track of IGMP
and MLD membership reports, R1 is also responsible for initiating the
creation of source and/or shared trees towards the senders or the
RPs.
There are multiple reasons for why network could potentially trigger
DR re-election. Some of the reasons are
1. R1 going down
2. Access interface towards shared LAN going down
3. Config changed with lower DR priority
When any of above network event occurs, PIM DR re-election would be
triggered. When a new DR is elected in shared LAN, new DR would be
responsible to build a multicast tree towards source / RP. There are
some cases, where traffic is crucial and the operator wants to have
minimum traffic loss with DR failure. To address this requirement,
this draft introduces a backup DR election procedure which would
minimize traffic loss during PIM DR failure.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] .
BDR - PIM Backup DR
With respect to PIM, this document follows the terminology that has
been defined in [RFC4601] .
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3. Applicability and deviation from draft PIM DR Improvement
[I-D.ietf-pim-dr-improvement] defines procedure to solve same problem
which was stated in the introduction section of this draft.
[I-D.ietf-pim-dr-improvement] introduces new PIM Hello options for
election of backup PIM DR.
This draft provides mechanism to elect BDR without using any new PIM
Hello.
4. Protocol Specification
4.1. PIM Backup DR (BDR) election procedure
[RFC7761] defines procedure for PIM DR election. PIM DR is elected
on interface "I" among all PIM routers for which "I" has received PIM
Hello. BDR election follows the exact same procedure and the second
best PIM DR on shared LAN to be chosen as BDR on interface "I"
BDR would perform each of the responsibility of PIM DR except it
would not forward traffic on shared LAN.
4.2. Existing PIM DR failure
When PIM DR fails, PIM DR re-election is triggered on shared LAN.
Since BDR is second best DR in LAN, it MUST take over immediately and
MUST start forwarding multicast traffic on shared LAN.
Again on a shared LAN, new BDR would be elected. and current BDR
would be the new DR.
4.3. Existing PIM BDR failure
When an existing PIM BDR fails, the shared LAN MUST have BDR re-
election using the DR election procedure from [RFC7761].
4.4. New PIM Router addition in network
When a new PIM router is added in shared LAN, It could be either one
of the below defined roles.
4.4.1. New PIM router eligible to be PIM DR on shared LAN
When a new PIM router is added in a shared LAN and has the highest
PIM DR priority configured, if a new router starts propagating its
configured DR priority right away, the existing PIM DR would give up
its role. Then there would be potential traffic loss till the new DR
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learns about membership states and builds a multicast tree to the
source or RP.
To avoid any such traffic loss situation, new PIM router SHOULD send
a PIM Hello with priority 0. After 2 (default value, SHOULD have way
to configure) PIM Hello interval or IGMP Query Interval (Which ever
is higher) it SHOULD start propagating its original configured DR
priority.
Even though a new PIM router propagating its priority as 0, it MUST
start building a multicast tree towards source / RP, This is So that
traffic loss could be minimized once it starts sending Hello with
configured DR priority.
For a brief amount of time, there would be multiple copies of flows
present in the multicast core, but a user SHOULD be able to configure
whether to send hello with 0 priority or a configured priority.
Depending on the application tolerance (Traffic loss Vs Extra traffic
in core) the operator can choose option whichever is suitable for
network.
After a PIM Hello or IGMP Query interval, the network would get
stable with only one DR and one BDR.
4.4.2. New PIM router eligible to be PIM BDR on shared LAN
It SHOULD follow the exact same procedure defined in the previous
section.
4.4.3. New PIM router is not eligible to be PIM DR or BDR on shared LAN
First a PIM Hello MUST be sent with priority 0. Once it has gotten
Hello from other PIM neighbors, it knows that it is not eligible to
be PIM DR or BDR. It MUST send configured PIM DR priority
immediately. It MUST not wait for next hello interval.
4.5. Initial case, All new PIM router coming up in shared LAN
In this case, initially each of the PIM routers would send Hellos
with priorities of 0. If a PIM router receives all Hellos with
priorities 0, it MUST send out a Hello with a configured PIM DR
priority. Since it is initial startup case, it would take up to one
Hello interval to converge.
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4.6. Benefit
1. Easy to implement as it uses an existing PIM procedure to elect
DR.
2. Does not introduce any new Hello option
5. Compatibility
6. Manageability Considerations
7. IANA Considerations
8. Security Considerations
9. Acknowledgement
The author would like to thank Stig Venaas, Tharak Abraham, Anish
Kachinthaya, Anvitha Kachinthaya for helping with original idea.
10. 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-04 (work in
progress), December 2017.
[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>.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601,
DOI 10.17487/RFC4601, August 2006,
<https://www.rfc-editor.org/info/rfc4601>.
[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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Authors' Addresses
Mankamana Mishra
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: mankamis@cisco.com
Sridhar Santhanam
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: sridsant@cisco.com
Aravind Paramasivam
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: arparama@cisco.com
Dr Imed Romdhani
Edinburgh Napier University
UK
Email: I.Romdhani@napier.ac.uk
Gyan S. Mishra
Verizon Communications Inc. (VZ)
13101 Columbia Pike FDC1 Rm 304-D
Silver Spring MD 20904
UNITED STATES
Email: gyan.s.mishra@verizon.com
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