Multicast over GRE between Linux server and Cisco Router

[jneiberger at gmail.com (John Neiberger)]

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 at 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
>