multicast and multiple nics

[iprebeg at freebsd.org]

On Wed, Jul 22, 2009 at 12:02:02PM +0200, Giulio Ferro wrote:
> This is something that's really been puzzling me lately...
>
> Freebsd 8 beta amd64 recently updated
>
> The box has 2 nics:
> (internet inteface)
> em0 : 192.168.1.1, netmask 255.255.255.0
>
> (lan interface)
> re0 : 192.168.2.1 netmask 255.255.255.0 (lan interface)
>        192.168.2.2 netmask 255.255.255.255 (alias 0)
>        192.168.2.3 netmask 255.255.255.255 (alias 1)
>
> I want to run ushare (/usr/ports/ushare). This program sends
> multicast packets to multicast address 239.255.255.250
>
> The packets should go to the lan, so I add the route:
> route add 224/4 -iface re0
>
> In order to do the test I switch off the firewall (/etc/rc.d/pf stop)
>
> I start the service, but no packets can be seen leaving the interface re0
> with tcpdump.

Can you try to sniff with other machine in that lan?

>
> Even If I ping a multicast address directly I can see no packets at all:
>
> ping -I 192.168.2.1 239.255.255.250

Please, try to use mcastread like this

mcastread -v4 -s 192.168.2.1 re0 239.255.255.250 1337

or mcastsend like this

mcastsend -i re0 239.255.255.250 1337

to check is there any mcast traffic. ( IGMP packets generated by
mcastread are mcasted to 224.0.0.22 ). 

There is also quite a bug already mentioned here. Something is
preventing proper setting of destionation MAC. It is seen as DMAC stays
unicast-like.

>
> I can't really understand why this doesn't work. I've also tried to enable
> multicast routing (mrouted), just defining the interfaces I want to use
> in /etc/mrouted.conf, but no luck. I'm not even sure if mrouted should be
> needed in this setup, anyway...

You don't need mrouted, AFAIK. It is needed only when you want deploy
mcast session in WAN.

>
> Can someone point me what I'm doing wrong?
>
> Thanks.
>
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