Area Types

We almost always configure area 0 as the first area in OSPF. This area is of type backbone and is critical to the topology. Standard/Normal OSPF areas can be placed anywhere and calculate efficient inter-area and external routes through the LSAs which propagate. However, where an area has a simple topology and does not have an ASBR or any virtual links, it can be defined as a stub area. Routing from a stub area is based on default routes flooded back into the internal routers from the ABR. There is a slightly more functional version of this called a not-so stubby area or NSSA. This does allow you to pass external routing information (for example, from RIPv2) back into the backbone.