OSPF question

Tech-Me-UP

Do you have to have an area 0 when configuring ospf.

My sybex book states that the area is irreverent to making it work as long as you use the same ASN, but later in the book it states the back bone must be configured as 0.

So what is the ruling?

Also in the example they show it has asn of 10 not 0….

Thanks,

Drakonblayde

Ok, first off, I may be wrong, but as I recall, OSPF doesn't use an ASN, it just uses an identifier for the process ID, and it's irrelevant if you use the same process ID on each router. You have to have at least one area, area0.

Examples:

Router(config)#router ospf 1

The 1 is process ID. This could 1 on this router, 72 on another router, it doesn't matter. Obviously it's a good idea to keep it vanilla among the routers so you don't get lost.... imagine if you had a PID of 1 on one router and 72 on another router, and you started trying to modify a PID 1 of 1 on the second router... you'd have two sets of OSPF running, which will consume your resources.

Router(config-router)#network 192.168.0.0 0.0.255.255 area 0

The network statements are where you configure your area statements, and those must be the same.

So the correct way to read that would be the process ID is irrelevant (not ASN) but the area number needs to be the same

rossonieri#1

yes sir, using ospf you have to type that area 0 ( area 1, area 2 or whatever area ) to indicate that your router is on one administrative domain area. the process id ( that router ospf 1 thing ) assign by your isp or your principal IT Dept.

dmaftei

Tech-Me-UP wrote:

Do you have to have an area 0 when configuring ospf.

You _must_ have area 0 in the OSPF domain. You _may_ have other areas, and you may have routers that belong to other areas only (so you won't see "area 0" on those routers), but for the OSPF domain to be functional there must be an area 0 in the domain.