[Xorp-users] Simple multicast configuration

Pavlin Radoslavov pavlin at icir.org
Sun Aug 12 10:47:00 PDT 2007


Sanchez <sanchezmk at yahoo.com> wrote:

>     Hurrayyyyyy, it works. Just merely running tcpdump on both
>     interfaces on the xorp box makes it work, without tcpdump it
>     doesn't work, I have no idea why, but it's sufficient for me
>     to continue on my project.
>     Thanks for all the help so far, I hope you can fix this in the
>     next releases, or if you can't reproduce the bug I can send
>     you my virtual machine files if you need them. Thanks again.

I guess the problem is in the FreeBSD driver for the (virtual)
network interface. If a multicast router is started on an interface,
the interface is suppose to be in ALLMULTI mode: it should snoop all
multicast packets and pass them to the kernel for further
processing. If the driver/interface has problem with snooping all
multicast packets, then the kernel and XORP won't receive them.
Running tcpdump puts an interface in PROMISC mode, where all packets
are snooped. Eventually, running an interface in PROMISC mode helps
with snooping the multicast packets as well.
If you run "ifconfig -a" before running XORP and/or tcpdump you
should see the ALLMULTI and PROMISC flags being set/reset.

FYI, the current LiveCD is based on FreeBSD-4.10 which is quite
old. For the next XORP release we are planning to use the most
recent FreeBSD release (6.2) for the LiveCD. Hopefully the ALLMULTI
driver problem is fixed in that FreeBSD release.

Regards,
Pavlin



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