I am in the process of learning-for-design-and-deployment OSPF. Here is the existing setup (based on a recent migration from Nortel to Cisco):
Corporate headquarter with two 6509s in HSRP mode, which play also the rols of inter-VLAN router ("s", if you think at one as passive, though, of course). The two have uplinks to a 3845, which connects (terminates) point-to-point via full and chanelized (sharing some channels with voice) T1s seven other locations. At the other ends I have 2825s, and, behind those, either 650xs or 450xs, doing inter-VLAN routing for those remotes.
Right now everything is statically routed (we opted for static routes in the first phase of migration, as we prefered the comfort of knowledge of such, during vendor change, in regards to total unfamiliarity with Cisco stuff, in the beginning). We are in a hub-and-spoke environment, thus al remotes connecting through the core router (3845) no direct connections between any remotes. Most of the remotes have dual or tri T1s connected back into the 3845 (with 7 sites we have filled the 3845 with plain multi-T1 as well as drop-and-insert (for data+voice) cards!)
I think it is time to move to a routing protocol, and OSPF seems to be a good choice, considering that it is also supported on some non-Cisco firewalls we have, which I plan to expand this to, in a later phase (site-to-site VPNs).
With the above background (sorry for the length - shooting for clarity), here is my question: what would be the pros and cons of the following options (if I correctly understand OSPF):
- area 0 on the ethernet interfaces of the 3845 connecting to the 6509s at the HQ, and also including those 6509s, then separate area for each WAN link + internal remote LANs
- same as above, but the external (serial) links of the 3845 also in area
- all sites in one area 0
Comments or pointers to similar designs would be greatly appreciated. Any other options?!?