In some email I received from Paul Kranenburg, sie wrote:
> I have a need to set up an on-demand dial-up PPP link on a machine which
> currently is also running `mrouted' to route multicast packets
> between two ethernet interfaces and an mbone tunnel.
> 
> The traffic through the PPP link is to be limited to TCP packets (just
> telnet and ftp are needed), so I set up an IPF filter for that.
> I thought that I might as well use those filter rules to keep
> the ppp daemon from dialing on spurious multicast traffic.
> But it didn't work. Even if I say `block {in,out} on ppp0 all'
> IGMP traffic is still going out on the interface.
> 
> Is this a know feature??

I assume you mean IGMP traffic going out actually goes out (it shows up
with tcpdump) and isn't just because it is redialling ?  I don't know how
the ppp interface works, with respect to dial-on-demand, but what you will
have to filter on is the tunnel IP addresses, not the multicast addresses.

What I think you need is this, in your mrouted.conf file:

phyint ppp0-ip-address disable

Darren