My guess is that this is because IGMP is a host-to-router protocol while PIM is for router-to-router signaling. IGMP joins typically flow from a multicast receiver to its local router. A GRE tunnel emulates a router-to-router connection, so you need PIM running on it for signaling. An IGMP join is really just a first hop host-to-router message and isn't intended to be routed, which is what would be necessary to get it over a GRE tunnel. HTH, John On Wed, Jan 9, 2013 at 8:51 AM, Brian Christopher Raaen < mailing-lists@brianraaen.com> wrote:
I am trying to set up multicast between a Linux server and Router using GRE. The GRE tunnel is up fine and I can see traffic go across it, but the router is not indicating it is receiving the IGMP joins that the server is sending. I have identical setting with another server attached to fastethernet0/1 and it is joined to the group fine, but I am not able to get the server to link to the router via GRE interface. Note that I have another server behind another router where the two routers do GRE and PIM and that on is working fine. Is there some reason that IGMP joins would not work across the GRE link, but another router using PIM would?
-- Brian Christopher Raaen Network Architect Zcorum