Subject: [pim] IGMP Group Membership Interval (draft-ietf-pim-3376bis) WAS: [Technical Errata Reported] RFC3376 (6725)

From: Alvaro Retana <[email-masked]>
Date: Wed, 27 Oct 2021 09:54:04 -0700

[Trying again — with the correct pim address. ]

Dear pim WG:

Hi!

Given the work on rfc3376bis, I want to bring the WGs attention to this new
report.

I am looking forward to any comments.

Thanks!

Alvaro.

On October 27, 2021 at 1:06:41 AM, RFC Errata System (
[email-masked]) wrote:

The following errata report has been submitted for RFC3376,
"Internet Group Management Protocol, Version 3".

--------------------------------------
You may review the report below and at:
https://www.rfc-editor.org/errata/eid6725

--------------------------------------
Type: Technical
Reported by: Nasir Ahmed <[email-masked]>

Section: 8.4

Original Text
-------------
8.4. Group Membership Interval

The Group Membership Interval is the amount of time that must pass
before a multicast router decides there are no more members of a
group or a particular source on a network.

This value MUST be ((the Robustness Variable) times (the Query
Interval)) plus (one Query Response Interval).

Corrected Text
--------------
8.4. Group Membership Interval

The Group Membership Interval is the amount of time that must pass
before a multicast router decides there are no more members of a
group or a particular source on a network.

This value MUST be ((the Robustness Variable) times (the Query
Interval)) plus (2 * Query Response Interval).

Notes
-----
A router resuming querier role (when current querier dies off) waits for
other querier timer value to be expired. This value is ((the Robustness
Variable) times (the Query Interval)) plus (one half of one Query Response
Interval). This value by default comes as (2 * 125 + 10/2) = 255. Whereas
GMI comes as (2 * 125 + 10) = 260. A group learnt with this value will have
its group timer value set to expire from anywhere from 260 + 10 (min 260,
max 270 due to random response from host in the interval of max response
time delay after a query). Now a new router resuming a querier role will
generate query after 255 sec. At this point of time the group timer left
will be in the range of (260 - 255) 5sec to (270 - 255 ) 15sec. Since the
query response can come anywhere between 10sec, Groups whose timer value is
less will expire and will result in traffic drop. Therefore it is
recommended to increase the default GMI value by one extra Query Response
Interval. That is - ((the Robustness Variable
) times (the Query
Interval)) plus (2 * Query Response Interval).

Instructions:
-------------
This erratum is currently posted as "Reported". If necessary, please
use "Reply All" to discuss whether it should be verified or
rejected. When a decision is reached, the verifying party
can log in to change the status and edit the report, if necessary.

--------------------------------------
RFC3376 (draft-ietf-idmr-igmp-v3-11)
--------------------------------------
Title : Internet Group Management Protocol, Version 3
Publication Date : October 2002
Author(s) : B. Cain, S. Deering, I. Kouvelas, B. Fenner, A. Thyagarajan
Category : PROPOSED STANDARD
Source : Inter-Domain Multicast Routing
Area : Routing
Stream : IETF
Verifying Party : IESG

---

From: Brian Haberman <[email-masked]>
Date: Wed, 27 Oct 2021 16:03:17 -0400

Hey Alvaro,
      I don't think I understand the rationale described in the erratum. 
All multicast routers that receive a Report for a multicast group will 
set the timer for that group to GMI. It will clear any state for the 
target multicast group if it doesn't get updated info before the timer 
expires. In the scenario described in the report, the router that 
resumes sending queries after the Other Querier Present timer expires 
will send a General Query, which should result in a host that has joined 
the target multicast group sending another Report and that will refresh 
the state for the group (i.e., reset the timer to GMI).

Regards,
Brian