IGMP fast-leave


trying to understand how "fast-leave" works; I do realize it's related to IGMP Leave messages and how they are processed by IGMP aware switches, but no more.

RFC2236 mentions this term only one time, without further explanations. As I understand, "fast-leave" (or as some manufacturers call it "immediate leave") isn't standard?

Would someone be so kind to explain me the machinery of this procedure?

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fast leave came in as part of IGMP v2.

RFC 2236 says a host"may" send a fast leave when leaving a group, so it isnt mandatory, but many client IP stacks always send it when exits a group.

a host sends a leave to "all routers" multicast. The router then sends a group specific query(s) to see if any hosts are left, and removes the group if there is no reply.

AFAIR default is 1 sec timeout and 2 queries, so the group should get dropped after 2 sec or so.

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So the gist of fast-leave is not to wait til group membership timers on multicast routers have expired, but quickly send a group-specific query and if not report were received, remove the group?

Is it the same way how Layer2 devices implement fast leave (sometimes called immediate-leave) ?

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