about multicast routing.

about multicast routing.

Post by Dean » Fri, 25 Feb 2000 04:00:00

Hi all.

I have 2 ethernet interfaces in my linux machine.
One interface(e.g. eth0) can only receive packets and it can receive
multicast packets. And the other interface(e.g. eth1) is normal one that
connected to local subnet.

What I want to do is when a PC in the subnet joins the multicast group,
my linux machine receive multicast packets from eth0 and route it to the
PC via interface eth1.

I have tried it with 'mrouted', but I don't know how to confgiure it.
Is it possible with 'mrouted' ?

If anyone has an idea about it, please help me.

Thanks in advance.


1. adding multicast route to the kernel

Hi all,

I have a question which probably has a very simple answer.  I'm trying
to insert multicast routes into the kernel using setsockopt with
MRT_ADD_MFC on an IGMP socket... just like most multicast routing

What I want to do is to be able to say "all multicast packets going to
<mcast addr> from any source coming in from <incoming interface>
should go out on <outgoing interface>".  Now, I've looked at smcroute
code and pimd code.  What should mfcctl.mfcc_origin be set to when I
do the setsockopt() call?  Should it be set to ?  That doesn't
seem to work.  What value signifies "all IP addresses"??

I looked at ipmr_input() in ipmr.c in the kernel sources and found
that it does a "straight" cache lookup.  I mean, it just takes the
source IP address and the destination multicast address from the IP
datagram and does a cache lookup.  It doesn't try to do a "wildcard"

However, I know that routing daemons like PIMD have to add routes of
the form
(*, G).  And I did find that they set mfcctl.mfcc_origin to
But I'm not sure how it works for PIMD.

Any help is greatly appreciated.


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