Subject: Restricting multicast traffic

From: Headbanger <[email-masked]>
Date: Tue, 1 Sep 1998 17:03:36 -0700 (PDT)

Hello all,

  I'm hoping someone can help me with this.  I have a Solaris machine
running mrouted3.8 that is an endpoint of a DVMRP tunnel.  Other mrouters
will connect to this machine via a multicast tunnel in the future.  No
hosts that are connected to this physical LAN will access the MBONE.  The
problem is the LAN that this mrouter is connected to is being saturated by
unwanted multicast traffic. 

  By eliminating this traffic, I can reduce network congestion that
everyone is screaming about.  I'll bet there is something minor to modify
in the mrouted.conf file but I can't find anything in the docs.  Anybody
have any ideas?  Setting boundaries maybe?

Thanks!

-Lance

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From: Tom Pusateri <[email-masked]>
Date: Tue, 01 Sep 1998 21:07:48 -0400

>unwanted multicast traffic. 

If there are no multicast routers on this LAN, then the LAN should not
be in the downstream interface list unless there are local group members.
In this case, mrouted would prune upstream and you should not be
seeing that much traffic. However, if you have a downstream router
then the multicast traffic will be put on the LAN waiting to receive
prunes from the downstream router. Some routers do not prune which
can cause this effect. mrouted 3.9beta3 will increase the
prune lifetime to ~2 hours upstream but if a downstream router
isn't pruning, it won't matter. But if pruning upstream is working,
using mrouted3.9beta3 will reduce the periodic broadcasts.

Another cause of this can be a bridged network with spanning tree
turned off. Then the bridges rebroadcast the multicast traffic
forming loops and using up your bandwidth. You can detect this
by looking for duplicate IP header IDs.

tcpdump is a fine tool.

>have any ideas?  Setting boundaries maybe?

Boundaries are for administratively scoped multicast.
You're probably seeing mostly global multicast traffic which won't
be scoped by boundaries.

Hope this helps,
Tom

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From: Cyndi Jung <[email-masked]>
Date: Wed, 02 Sep 1998 09:10:23 -0700

I had this exact same problem when I put my tunnel on Solaris a
few years ago.  The solution was to add another physical interface
to the mrouter - it wants two, and the tunnel counts as one and
if the only other interface you give it is the LAN it is sitting on,
it will use that.  Once I had the second interface, it stopped
dumping the multicast traffic back onto the LAN that it was receiving 
the tunneled traffic through, cutting the traffic back considerably.

Cyndi