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Re: Simple multicast question

Frank Kardel <> writes:

> If I were to
>  1) create an IPv4, DGRAM (UDP) socket
>  2) bind that to

This seems bizarre to me.  bind sets the source address, which is a
separate issue.

>  3) do a IP_ADD_MEMBERSHIP for address and imr_interface =
> INADDR_ANY on that socket

that should join on the interface of the default route.

>  4) start recvmsg-ing on it

> The thing is I see the packets via tcpdump, IGMP seems to work
> correctly, but nothing arrives in the
> program. Am I missing something or do we have a multicast reception

Are you seeing IGMP membership reports from your box on the interface
you are seeing mcast on?

> problem in NetBSD
> (even for older versions of -current)?
> Short investigation gave that mcast packets can be dropped for the
> mcast-address not being
> in the receiving interface's mcast-address-list (ip_input.c) or when
> the dst-addr/port is not found (udp_usrreq.c).
> The interface is wm0 and ifconfig shows the multicast counter going up
> as does the CANTFORWARD IP-statistics counter.

'netstat -ai' should be useful.  but on a netbsd-5 box it isn't showing
OSPF groups joined even though ospf (quagga) is running fine.

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