RFC 3376, "Internet Group Management Protocol, Version 3", October 2002

Note: This RFC has been updated by RFC 4604

Errata ID: 6725
Status: Held for Document Update
Type: Technical
Publication Format(s) : TEXT
Reported By: Nasir Ahmed
Date Reported: 2021-10-27
Held for Document Update by: Alvaro Retana
Date Held: 2022-01-31

Section 8.4 says:

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).

It should say:

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).

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AD Notes:

I am changing the status of this report to Held for Document Update. The WG is discussing what the best way to address it is: https://mailarchive.ietf.org/arch/msg/pim/Im8go1fjyVad7jyhGg1bgnW93qM/

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