OSPF Pocess-ID

[M.Sultan]

Hi guys

I understand the purpose of Process-ID in OSPF domain, it's locally significant, two adjacent routers can form adjacency even with two different Process-ID.

Consider the Diagram :

R1 Area 0      R2 ABR          R3 Area 1

when i put interfaces from ABR into different Process-ID it doesn't form adjacency. 

Like: in ABR

#Router ospf 20 

#interface ethernet 0/0

#ip ospf 20 area 0

----------------

ABR #router ospf 40

#exit

#interface ethernet 0/1

#ip ospf 40 area 1

it does not form adjacency between router R1

Area 0 and R3 Area 1.

[Joseph W. Doherty]

"if we put each interface into different Process-id, No adjacency will form."

Again, you need to be clear what you mean by

adjacency

, as for OSPF, it generally refers to two neighboring OSPF routers establishing an OSPF relationship between themselves.

On the same router, using different OSPF process IDs, there would be two distinct OSFP databases, one for each process ID. 

Adjacency

doesn't apply between process IDs.

To clarify this even further, for process-ID 20 you might have connections to two different routers, one in

area 0 

and one in

area 1

, and they would establish adjacency with R2 for both

areas 0 and 1

would be in one

OSPF topology.

You can do this again for process-ID 40, i.e. have another two routers, with adjacency with R2, in

area 0 and area 1.

However, although there's two sets of

area 0 and area 1

connected to R2, they are that, two sets, i.e. two

area 0s, and two area 1s

, and the two

area 0s

are NOT the same

area 0

, ditto for the two

areas 1.

What can make the forgoing confusing, R2 will route between both OSPF

topologies

, i.e. process-ID 20 packets can be directed to process-ID 40, and the converse, because both are combined in one routing table on R2 (unless using VRF).  But, by default, a non-R2 router in one of the two OSPF

 topologies

, would not "know" of the OSPF routes within the other OSPF

topology.

[MHM Cisco World]

R1(OPSF1AREA0)-(OPSF1AREA0)R2(OSPF2AREA1)-(OSPF3AREA1)R3 

here since area match between two routers the adj will form even if process is mismatch

Now'

In R2 since you run two process you need

redistrubte

from one process to other.