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On 2011-03-30, Andrew Lunn <andrew@xxxxxxx> wrote: >> It's being sent via a socket that's bound to a specific interface, so >> I wouldn't think that would be a problem. > > Ah, O.K. > > Maybe try it anyway? > >> I can see that if you're sending from an unbound socket, you might >> want a way to specify which interface to use for sending multicast >> packets. But without such a route, the only thing that makes sense to >> me is "send it out all of them". > > And on a multi homed machine that might result in the group receiving > two copies of the packet when both multicast routers pick it up and > send to the RP. True. According to RFC1112, you only send a multicast packet on one interface. If the application doesn't specify an interface, a default interface is used. IOW, discarding the packet is not correct: Second, for hosts that may be attached to more than one network, the service interface should provide a way for the upper-layer protocol to identify which network interface is be used for the multicast transmission. Only one interface is used for the initial transmission; multicast routers are responsible for forwarding to any other networks, if necessary. If the upper-layer protocol chooses not to identify an outgoing interface, a default interface should be used, preferably under the control of system management. It turns out this was fixed in the FreeBSD sources in 2001: http://svn.freebsd.org/viewvc/base?view=revision&revision=79830 http://svn.freebsd.org/viewvc/base?view=revision&revision=79836 I'll work up a patch... -- Grant Edwards grant.b.edwards Yow! I'm having an at emotional outburst!! gmail.com -- Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss