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Date:      Thu, 04 Jan 2001 14:49:15 -0800
From:      Wilbert de Graaf <wilbertdg@hetnet.nl>
To:        net@freebsd.org
Subject:   igmp and if_down()
Message-ID:  <3A54FDEB.FB442E82@hetnet.nl>

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Some time ago I worked on an implementation of IGMPv3 on FreeBSD.
Somebody I know is using it to test his router implementation on a
terminal / ppp server. He told me the following:

* a socket subscribes to some group on the ppp interface, and he sees
IGMP reports
* hangs no up, and dials in again and the IGMP messages continue

He thinks this is not okay, but I'm not sure. You could argue that
membership on a non-existing interface is impossible. On the other hand,
it's get more complicated if you do remove membership: are you going to
inform those sockets on which you removed their membership ?

What do you think ?

Btw.
When I looked at the code I came as far as net/if.c in the fucntion
if_down(). The documentation says that protocols should be informed
here. I took a peek at the Linux code and they do notify IGMP, which
removes all memberships on the interface that's going down.

Wilbert


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