multicast forwarding

multicast forwarding

Post by Fabio Lopian » Thu, 13 Mar 2003 03:28:38



Hi all,

I'm trying to forward some multicast traffic trough a couple of networks.
I'm using ip tunneling (gre) and messages arrives from the source on
network A to the destination on network B.
Now I would like that the destination host forwards the packets received
from the tunnel interface to the ethernet interface.
Unfortunately adding a route did not help...

More in detail:

Source Network is "192.168.215/24", Destination Network is "192.168.231/24"
(These networks are connected trough a series of routers and firewalls)

on Source Linux Host (192.168.215.28) I did :

# insmod ip_gre
# ip tunnel add mcast mode gre remote 192.168.231.66
# ip link set mcast up multicast on
# ip addr add 192.168.215.28/24 dev mcast
# ip route add multicast 224.13.0.0/16 dev mcast

on Destination Linux Host (192.168.231.66) I did :

# insmod ip_gre
# ip tunnel add mcast mode gre remote 192.168.215.28
# ip link set mcast up multicast on
# ip addr add 192.168.231.66/24 dev mcast
# ip route add multicast 224.13.0.0/16 dev eth0

on the same network, a windows host (192.168.231.61) must receive
all multicast traffic without joining the multicast groups
(it already receives other multicast traffic, on different groups,
 generated from the destination host).

On both linux hosts the kernels have been compiled with full
support for multicast.

When I generate some multicast packets on the Source Host,
these packets are routed trough the mcast device and pop
up on the Destination host from the local mcast device.
I would like that this host forwards these packets to
the ethernet. But this does not happen.

(following commands issued on the destination host)

# tcpdump  net 224.13/16
Kernel filter, protocol ALL, TURBO mode (575 frames), datagram packet socket
tcpdump: listening on all devices
19:17:21.646825 mcast < 192.168.215.28.33335 > 224.13.3.76.31763: udp 105 (DF)
19:17:21.696825 mcast < 192.168.215.28.33335 > 224.13.3.76.31763: udp 107 (DF)
19:17:21.746825 mcast < 192.168.215.28.33335 > 224.13.3.76.31763: udp 108 (DF)
...
I expected to see the same packets exiting from eth0.

I tried to

# echo 1 > /proc/sys/net/ipv4/conf/eth1/mc_forwarding

but

bash: /proc/sys/net/ipv4/conf/eth1/mc_forwarding: Permission denied

# cat /proc/version

(gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-85))
#1 SMP Wed May 16 04:29:16 EDT 2001

Do you have any idea ?

Thanks for your attention,

Fabio Lopiano