[Xorp-users] multicast over GRE tunnel

Pavlin Radoslavov pavlin at icir.org
Sat Feb 10 14:19:01 PST 2007


> 	Just a message to let you know that the setup below just works. But 
> there was a few details missing. First when configuring the linux side 
> of tunnel I had to explicit set the TTL with the command ifconfig tun0 
> ttl 64. I took a while to found this... my firewall showed packets 
> coming in one interface but didnt leaving on the other! Second, I had 
> to disable rp_filter on xorp router! dont exactly know why. Btw there´s 
> a missing detail on my setup description. Xorp router has only one 
> ethernet card. It´s on the same net as desktops.

Great!
I should had realized earlier that there could be missing pieces in
your GRE tunnel setup.
For the record, below is an example (taken from pimd README.config)
for setting a GRE tunnel.

1.1 GRE tunnel between two machines (host 11.11.11.11 and
  33.33.33.33)

Physical interfaces:    [11.11.11.11]         [33.33.33.33]
GRE tunnel:              22.22.22.11<--------->22.22.22.33

==== host 11.11.11.11 (GRE interface 22.22.22.11)
echo 1 > /proc/sys/net/ipv4/ip_forward
echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
ip link set gre1 down
ip tunnel del gre1
ip tunnel add gre1 mode gre remote 33.33.33.33 local 11.11.11.11 ttl
127
ip addr add 22.22.22.11/24 peer 22.22.22.33/24 dev gre1
ip link set gre1 up multicast on


==== host 33.33.33.33 (GRE interface 22.22.22.33)
echo 1 > /proc/sys/net/ipv4/ip_forward
echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
ip link set gre1 down
ip tunnel del gre1
ip tunnel add gre1 mode gre remote 11.11.11.11 local 33.33.33.33 ttl
127
ip addr add 22.22.22.33/24 peer 22.22.22.11/24 dev gre1
ip link set gre1 up multicast on

I just added a subsection to the XORP User Manual for configuring
a multicast tunnel. For now the examples are for GRE and OpenVPN.
If someone has working examples for other tunnels/setups, please let
me know so I can include them in the document.

Pavlin



More information about the Xorp-users mailing list