socket option IP_MSFILTER questions and observations

Hi,

I'm trying to use source specific multicast by setting the IP_MSFILTER socket option. I noticed i need to join the group with IP_ADD_MEMBERSHIP before setting the source filter. This is not the behavior i expected after reading RFC3678. A potential issue i'm thinking of with this approach: an IGMP report could be sent after joining a group but before the filter is set.
Is there a way to prevent this?

Thanks,
Cedric

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RFC3678 doesn't say that an IP_MSFILTER will join a group
automatically. The model is that you join a group once and then dynamically set the source filters as they change over time.

Adding or changing the source filters triggers a new report
but you can use IP_ADD_SOURCE_MEMBERSHIP which does explicitly join a group with a source filter. In the kernel, this is done with an "any" join followed by setting a source filter which actually will result in 2 reports too, if there are no other processes using that group.

                                                        +-DLS

From: Cedric Jehasse <[email protected]>
Date: Mon, 26 Mar 2012 17:40:56 +0200

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