Bridging over GRE tunnel

Question

Dear expert,
Currently I have problem running bridging over GRE tunnel.We are using cisco 3640 but somehow under tunnel 0, the is no 'bridge-group 1' command.We are trying to get the IOS that support the command under tunnel 0 but to no avail.Can someone help me ? Thanks
--ran

Answer 1

It's a hidden command.  Even do, you might get a warning messasge stating this is obsolete and unsupported, it still technically a valid configuration. Legacy, but works.
Keep in mind there are better solutions for this kind of connections.  But you can try it, it's simple anyways.
Host1---Fa0/0--R1-------------GRE------------R2--Fa0/0---Host2
1. Create a Loopback intf. on both routers and ensure L3 connectivity between them.
2. Create bridge:
router(config)#bridge 1 protocol ieee
3. Create a GRE tunnel interface (dont configure IP's):
router(config)# interface tun0
router(config-if)# tun source loopback x
router(config-if)# tun destination <other router loopback ip>
router(config-if)# bridge-group 1
**This is a hidden cmd. You will get a warning message, but ignore it**
3. Attach Physical Interface to Bridge as well:
router(config)# interface Fa0/0
router(config-if)# bridge-group 1
4. Configure the Hosts IP addresses to be on the same IP Segment and validate communication between them.
You can try this on GNS3 as well.  I made a diagram and a brief explanation at another thread, but really don't remember how to get to it.
Once again, this is legacy and there are better ways to achieve this. But for small implementations this is valid and easier.  It also helps to understand the newer versions/enhancements to this as well. 
HTH