Wan Routing-How is this working?

[jackwalker]

    I work for a technical college that includes a main campus and five remote campuses. Last Friday we switched carriers to TWC metro-e from another carrier. The old carrier was routing mpls from the main campus to the remote campuses through their cloud and every router interface (either g 0/0 or fa 0/0) resided in the same network. Now all remote campuses are connected to the TWC local office via layer 2 and then a 50 mb aggregate metro-e link delivers all of the traffic to the main campus. It is a very basic hub and spoke config. We are using layer 3 routed links to each of the sites with the main campus switch being the .1 and the remotes being .2, .3, .4, .5, & .6 in a standard class C network. We used EIGRP on each router in the same autonomous system. This seems to be working fine, but I'm not sure how. Everyone of those routers is in the same network sends data to the main campus router which is also in the same network. I would think for this to correctly work correctly the routers would to reside in separate networks or subinterfaces be setup. Can anyone shed some light on this for me? BTW Each FA 0/1 or g 0/1 interface is connected to a separate /24 network on the individual campuses. The main campus switch is a layer 3 Nexus 7010.

Thanks!

Jack      

[vmiller]

Without seeing the exact syntax of how EIGRP is setup,  I'm fairly comfortable is saying this is a pretty vanilla setup for the routing protocol. For any interior gateway routing protocol to function there needs to be some common address scheme. In your case, the hosts you listed are all part of one subnet (I'm guessing). that takes care of the Routers understanding who their neighbors are.

Within each config, it is possible to have multiple seperate "networks" and let the Routers advertise what ever they need to advertise. Bot for the routers to see each other there needs to be a  common ground.

Subinterfaces are nothing more than a logcial means to break up an interface for other routing uses. In your case, with one physical path out, it doesnt make sense to use subinterfaces on the spoke side.