Dude… It’s Like Totally Stubby, Man!

stubnet.jpg

I know I haven’t posted much lately, with studying for the Cisco BSCI and working on my kitchen floor, but I always get a bit of a kick when reviewing OSPF routing protocol, specifically when talking about stub areas. This is because of the naming of these various types of stub areas:

Stub Area
Totally Stubby Area
Not So Stubby Area (NSSA)
Totally Stubby Not So Stubby Area (sounds kinda contradictory, doesn’t it)

That’s a lot of subbiness going on here. What is it all about, anyway? In a nutshell, the various stub areas in OSPF are configured as such to limit the types of LSA (link-state advertisements) that the router receives, reducing its routing table size. The particulars of each type are a lot to get into in a post, but visit Cisco’s site on the topic to learn more.

Luckily the configuration itself is fairly straightforward. All commands are within the OSPF router config mode.

For a stub area:

area area-id stub (where area-id is the number label of the area in question)

For a Totally Stubby Area:

area area-id stub no-summary (no-summary only required if it is on an Area Border Router, or ABR)

For the Not So Subby Area

area area-id nssa

And for Totally Stubby Not So Stubby Area

area area-id nssa no-summary (again, no-summary only required on an ABR)

Of course, as stated, there’s a bit more to it, but Cisco generally does a good job with information on various topics on their web site. The article also mentions Virtual Links. All areas in an OSPF network are required to be connected to Area 0 (the backbone area). Virtual links are a sort of “band-aid” you can use when an OSPF area cannot be physically connected to Area 0.

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