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Cisco Information Technology Networking

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.

By Jim Ashley

Husband and Dad. IT professional tech guy and woodworker. Will bring some sort of camera with me outdoors.

2 replies on “Dude… It’s Like Totally Stubby, Man!”

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