socket option IP_MSFILTER questions and observations

socket option IP_MSFILTER questions and observations

[Cedric Jehasse]

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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Re: socket option IP_MSFILTER questions and observations

[David Stevens]

> 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.
        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.

> 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?

        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

Re: socket option IP_MSFILTER questions and observations

[David Miller]

From: Cedric Jehasse <cedric.jehasse@softathome.com>
Date: Mon, 26 Mar 2012 17:40:56 +0200

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> unauthorized use or dissemination is prohibited. If you are not the
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> inform the sender.

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