[Openswan Users] L2TPD with multicast

[andy huang]

Hi,

I have installed OpenSWAN as well as L2TPD on Ubuntu
7.10. Here is the configuration I have:
   NAT(192.168.11.0/24)---------------Corp Network
   |
   |
Ubuntu
(L2TPD/---------NAT(192.168.0.0/24)---------Windows XP
OpenSWAN)

So the Ubuntu has following eth interface:
eth0: 192.168.11.2, eth1: 192.168.0.3.
Windows XP client PC was able to connect to it and
ppp0 is 172.16.0.0/24. 
But the multicast client on the Windows XP can't join
the group on the Corp network thru L2TP tunnel. 
I have enabled IP Forwarding: echo 1 >
/proc/sys/net/ipv4/ip_forward and TTL is big enough.
Ethereal shows that IGMP message was sent to ppp0, but
not eth0. 
Here is some info:
/proc/sys/net/ipv4/conf/eth0/mc_forwarding=0
/proc/sys/net/ipv4/conf/eth1/mc_forwarding=1 
/proc/sys/net/ipv4/conf/ppp0/mc_forwarding=0.

How can I enable multicast forwarding/routing thru
L2TP tunnel? TIA.