OSPF areas and domains

[rtwwpad]

Hi

I am a little confused wrt to OSPF after reading Jeff Doyles Intro to Routing Vol I on the CCIE booklist.

He says that in the command

router ospf 12

the process-id only has local significance. If this is true, then how do we stop different OSPF domains talking to each other.

eg: Company 1 connects to company 2. Both are running OSPF. If we connect via ABSR's then we should be alright as they define the edge of the domain. But if someone somehow messes up and doesn't make it an ASBR then will the tables all start to mash and merge?

phil

[prafuljaded]

You can have independent,multiple OSPF processes running on a single router like "router ospf 10" and " router ospf 12". So now you are running two different OSPF processes on the router, which is not recommended.The networks,area you define under each OSPF process makes the difference in exchanging routing updates.Unless you define the two ASBRs in same area (area 0)they wont exchange information. Also you can stop routing info to pass across using appropriate distribute-lists

[arraman]

Hi,

use "passive-interface" to avoid routing updates/neighbor established through unnecessary interfaces

Arun

[rtwwpad]

Thanks for the responses, however this is where i run into problems. Assuming I run multiple processes on a single router. How does the routers it connects to know that they are running the right OSPF information.

Perhaps an example will help explain my confusion.

I have two domains. Domain A consists of Area 0 only and runs 10.x address space. domain B consists of Area 0 and Area 1 and runs 172.16.x address space. I need to redistribute.

Router Superman links the two domains together. The config on Superman which has just two ethernet ints E1 - 10.x, E2 - 172.16.x) is

router ospf 10

network 10.10.10.1 mask area 0

router ospf 20

network 172.16.1.1 mask area 0

As long as I ensure that the two ospf domains are kept in seperate process's on superman then it should all work. If I am foolish enough to try and run both networks as one process, so I entered

router ospf 10

network 10.10.10.1 mask area 0

network 172.16.1.1 mask area 0

then I would get myself in a pickle. Phew, I think I just explained it to myself. Can someone just verify I am not talking twaddle to myself.

phil