Multicast/IGMP Join in FreeBSD 6.1

Loren M. Lang lorenl at
Tue Jun 20 05:39:30 UTC 2006

Mayo, Richard A RDECOM CERDEC STCD SRI wrote:
> Can anybody tell me how to configure the multicast groups my computer will attempt to join?  I when my computers boot, I can see a IGMP join request for, but I would like to add more.

When a program opens a socket for listening, it requests which groups it
will listen on using an option in setsockopt(), and bind().  When the
program closes the socket or exits, the group is left.  The IGMP
Join/Leave messages are only needed if you have multicast capable
routers and are running a multicast routing protocol like PIM and want
messages from other subnets.  Any group can be joined that is
broadcasted locally without those messages.  If you put your network
card in promiscuous mode, as is done by most packet sniffers, you should
be receiving all locally transmitted packets, including multicast.

> Any suggestions?
> Rich Mayo
> SRI International
> x76435
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Loren M. Lang
lorenl at

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