Multicast routing with VLANs

[Bruce M Simpson]

Hi,

On Mon, Apr 25, 2005 at 07:21:22PM +0200, Eivind Hestnes wrote:
> I'm trying to get mrouted to route multicast traffic between multiple 
> VLANs on a FreeBSD 5.4-RC3 machine. Mrouted starts as expected, and 
> according to /var/log/messages it's running - but the multicast routing 
> itself don't work. While Googling, I noticed in kern/78821 
> (http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/78821) that FreeBSD 
> fails to set the ALLMULTI flag on the parent device when using the 
> if_em(4). I have tried to set the ALLMULTI flag manually, but with no 
> further success - The flag won't set.
> 
> I need the multicast routing to get Norton Ghost work properly, and 
> currently I'm a bit stuck..

It is very very possible that ALLMULTI doesn't work right on cards which
have hardware VLAN tagging support, though I haven't investigated it.

For situations where the underlying hardware or card firmware cannot support
the notion of ALLMULTI (receive all multicast datagrams promiscuously), it
would be necessary to spoof it up by putting the hardware into promiscuous
mode.

NetBSD has a flag called M_PROMISC. Why is this relevant? Well, one thing
I've noticed is that if you're running regular unicast forwarding on a box,
and then put one of the interfaces into PROMISC mode, the danger is that
the box will then begin trying to forward the datagrams it's just forwarded.

We'd need a way to differentiate between traffic addressed to us and not
addressed to us by MAC address when forwarding.

Sadly ENOTIME at the moment for writing patches. :-(

Regards,
BMS