All things related to multicast

["Marshall Eubanks" <>]

On Mon, 25 Mar 2002 09:58:01 -0500
 Dave Hartzell 
<>
 wrote:
> Hi-
> 
> Just wondering if anyone has messed with GRE, Multicast
> and Linux.  What 
> I'm doing is setting up a GRE tunnel between a multicast
> enabled Cisco 
> and a Linux box.  I'm doing this because the network the
> Linux box is on 
> cannot support multicast at this time, and I'm a glutton
> for punishment.
> 
> Everything works well on the Linux box when receiving
> multicast from 
> Abilene, but sourcing a stream from the Linux box doesn't
> work.  The 
> packets don't get routed to the tunnel, just out the
> local Ethernet 
> device, even though there is a multicast entry in the
> routing table 
> explicitly pointing at the gre tunnel interface.
> 

Various questions for various possibilities -

Are you running PIM-SM or something else ? Are you running
MBGP, or is this interior routing only ?

What is doing the routing on the Linux side ?
 
Are you dealing with the Linux sourced 
IGMP traffic on the Linux side of the
tunnel - or is it going through the tunnel ?

PIM-SM specific : Are there joins coming _out_ of the GRE
tunnel towards the Linux box ? If your first hop router is
before the tunnel, then joins have to traverse it for it to
send the data. It could thus be a routing problem on the far
end.

Are you doing MSDP ? Are you trying to put MSDP unicast
traffic through the tunnel ? Could your MSDP SA messages be
avoiding the tunnel and thus fail RPF checks ?

Regards
Marshall Eubanks

> Any ideas?  I'm running 2.4.14...maybe something is
> broken?
> 
> Thanks!
> 
> Dave Hartzell
>