Yeah, I think that will work but on your GRE routers you need two different route statements.
For example:
On GRE-A a specific route points to the PT of your TL to reach the GRE-B router FE0/0 interface. You need this route to build the GRE Tunnel from GRE-A to GRE-B.
Then of course you do the same on the GRE-B side pointing to GRE-A, interface FE0/1.
Next you have to route your subnets
through the tunnel interface. Just treat the tunnel interface like any ordinary physical interface and either configure static routes or run a routing protocol through the tunnel.
I've only configured GRE tunnels on 2800 and 7200 routers so I'm not sure if this config would be the same as on your 2611s but you can verify against the Cisco website easy enough. Here is a typical tunnel interface config:
interface tunnel1
ip address 1.1.1.1 255.255.255.252
tunnel source 10.x.x.x
for example, this would be your GRE-A router interface connected to the TL
tunnel destination 20.x.x.x
and this would be GRE-B interface FE0/0.
Of course, you would do the exact opposite on the GRE-B router using 1.1.1.2/30 for the tunnel interface ip address.
Hope I'm not going over details that you already know.
Now you have to route traffic through
interface tunnel1 tunnel. Although, in your situation, it might be enough to use the
ip directed-broadcast command on the tunnel interface as you are only attempting to transport DIS UDP broadcast and not normal unicast traffic. You'll also probably need to use the
ip directed-broadcast on the interface that connects the GRE routers to the Bridge routers. Unless adding the interface to the Bridge group is working. Not sure about that particular detail as I don't have any experience with bridging through a router.
Once the GRE Tunnel is up it's easy to route traffic through the tunnel, including multicast, but I'm still unable to find any information that specifically indicates that a GRE tunnel can process broadcasts.
It's funny, when I search Google for broadcasts through GRE tunnels I keep coming up with your original request as posted on Tek-Tips and some other forum.
One thing you have to keep in mind when using GRE tunnels through the TL is the packet size increases. GRE adds a new header onto the original IP packet resulting in increase packet size. I believe the GRE header adds an extra 24 bytes; 16 bytes of new source and destination IPs and 4 bytes for the GRE header.
I don't know how large the DIS packets are, maybe not big enough to worry about, but if there is a problem you can tweak the TACLANE around the MTU size if needed.
If you can configure the ip directed-broadcast command on a tunnel interface I don't see why this shouldn't work.
I really wish I was back in my lab, I'd set this up to see if it works. I'm dying to know...
Good luck and let me know how it works out,
Jimi