OSPF Areas (Part 1)

Im starting a series of OSPF post to both follow up on my OSPF network types series (which can be found here) and to also dig deeper into the different areas available within OSPF and how each controls what LSAs and routes enter and exit an area.

Throughout these post Im going to run both IPv4 and IPv6 side-by-side in order to demonstrate both OSPFv2 and OSPFv3 and their minor differences.

The six area types used by Cisco routers for OSPF are as follows.
  • Backbone
  • Normal
  • Stub
  • Totally-Stubby 
  • NSSA (Not So Stubby Area)
  • Totally-NSSA 
I plan on breaking each on into their own separate post to keep this series clean.

The Topology

Here is the topology I will be starting out with. Nothing special. 10.0.xy.0/24 and 2001:cc1e:xy::/64(eui-64) are configured for the links between routers. "xy" represents the two routers on the link. The three "local networks" shown on both area 2 and 3 are represented by using loopback interfaces and are added to the area, not redistributed.

Configuration is pretty straight forward so I'm not posting the configs.

For this series your gonna need a firm understanding of both basic OSPF and OSPFv3 for IPv6 routing. I do suggest reviewing my IPv6 Routing post along with Marko Milivojevic, IPExpert blog entry on OSPFv3 LSAs.

Now lets get this ball rolling!!