Multicast over GRE VPN tunnels.

[JeremyTurlin_2]

Hi Guys,

I've got a rather large enterprise network that has multicast enabled and working through most of it, except our VPN spoke sites.  I will see through group that I want subscribers to join in the mroute table on the spoke router but I will the subscriber will not see the video feed.  This works at other sites.  I have a test tool called mcdiag that I have used to test multicast to the site.  With it I will setup a server at my desk, and remote to the site, and attempt to join the mc stream.  This works just fine.  Joining the video stream does not.  The only differences are that my desktop is in a different location than the video source, and the traffic is different.

Any ideas where to start troubleshooting?  Any help is appreciated.

[Fabrice Ducomble]

I would start checking the size of mcast packets since you have certainly a lower MTU through the tunnel.

If you use a software router (7200, ISR,etc...), you can for example use cache headers features '(config)#ip multicast cache-headers' and check headers of forwarded mcast packets with sh ip mpacket detail

Thx,

Fabrice