[openib-general] Re: ipoib send-only vs full join

[Hal Rosenstock]

On Tue, 2006-04-04 at 16:37, Roland Dreier wrote:
>     Sean> When does ipoib join a multicast group for send and receive
>     Sean> membership?  It looks like it joins the broadcast group for
>     Sean> send/receive, but all other groups are send-only.  Is this
>     Sean> correct?
> 
> Not quite.  It joins for receive when the networking core asks it to
> receive multicasts on a given group.

There is a setsockopt for adding a IP member which causes this:

   ret = setsockopt(s,
                     IPPROTO_IP,
                     IP_ADD_MEMBERSHIP, ...);


You should be seeing a number of full joins (like for some 224.0.0.x
addresses).

> It joins send-only when it has a
> packet to send for a group it hasn't joined yet.

That occurs when IPmc is doing the sender role to a IPmc group without
previously joining the group via the setsockopt mentioned above.

-- Hal

> 
>  - R.
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