OSPF Backbone Area and the WAN I am working on a new network deployment, and have run into an interesting question... Should the OSPF area 0 be extended across a WAN's point to point links (thereby creating more border routers), or should one's WAN Aggregation router serve as the ABR for each area? Consider the following: !OSPF Diagram In **Scenario 1** , R2, assuming area 1 is a totally stubby area receives only a default route, thereby reducing WAN bandwidth... I think? In **Scenario 2** , R2 receives many more routes. This seems like a trivial question, but I feel it may have a performance impact at scale. What is the best practice for extending area 0 across a WAN?

There is no one "best practice," but rather several "good practices" and a few "not-so-good practices."

Generally speaking, if you have multiple areas, you want the hub and spokes in the same area, and summarize between the hub and the rest of the LAN network. You can make the whole hub and spoke area totally stubby.

Another possibility is to break up the spokes into a few (no more than 2-3) areas, with the hub as the ABR. The most important factor that would make this design preferable is the relative instability of your WAN and remote LAN links. If you have a lot of links going up and down, this will affect the amount of flooding over the WAN and therefore the link utilization. But for 50 routes or so, that shouldn't be a problem for a T1.

Here is some more design information.