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.

[Flavio Miranda]

Hello,

 They are in different area right? If I understood correctly, you put on side in

area 0

and another side

 area 1

. They will form adjacency if they belong to the same area.

[M.Sultan]

ABR router means connect neighbour area to

area 0.

will form adjacency even in two different area but should be connected directly to

area 0 or virtual linked.

[Joseph W. Doherty]

"ABR router means connect neighbour area to

area 0."

Again, only correct within the same OSPF topology.  What you're describing you want to do creates two OSPF topologies.

"will form adjacency even in two different area but should be connected directly to

area 0 or virtual linked.

"

Actually an OSPF neighbor adjacently requires both routers to be within the same area.

Unsure why you're referencing virtual links in this context.

[MHM Cisco World]

The area mismatched make ospf failed not the process id

[M.Sultan]

R1 is in area0

R2 is ABR one side to Area 0 the Other side put in area 1

R3 is in Area1 

there is no mismatch, 

[MHM Cisco World]

It should work I run lab do same R1 is

using ospf 100 with area 0 and ospf 110 with area 1 to R2 and R3

 
it work 
recheck the IP and subnet you use in each interface 

[Joseph W. Doherty · Accepted solution]

"R2 is ABR one side to Area 0 the Other side put in area 1"

Only true if R2 has

areas 0 and 1

in same topology, but it does not!  I.e. different OSPF processes, on R2, create two OSPF

topologies/domains.

"there is no mismatch,"

Well, there's very likely something wrong in your configs.  @Flavio Miranda and I noted it should work, I and @MHM Cisco World showed examples that it does work.

[M.Sultan]

It seems you are experienced and have hands on lab.

However i found the confusion and solved the problem it is quite same as your explanation.

in R2 Two interfaces from

area 0 and 1

should run within same Process-ID which i created two different ospf domain in that case we need route

 redistribution ?

Thank you 

[Joseph W. Doherty · Accepted solution]

Yes, correct.

[Joseph W. Doherty]

It should, but as you've haven't posted the complete relevant configs of the 3 routers, cannot point to configuration issues.

BTW, although adjacency should form between R1 and R2, and between R2 and R3, you do understand R1 would be unaware of R3 and R3 unaware of R1?    Are you also aware R2 is NOT an ABR?

Also BTW, got the following using Packet Tracer:

R1:

interface GigabitEthernet0/0/0
 ip address 192.168.1.1 255.255.255.252
 ip ospf network point-to-point
 ip ospf priority 1
 ip ospf 1 area 0

Router#sh ip os ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.1.2       0   FULL/  -        00:00:35    192.168.1.2     GigabitEthernet0/0/0

R2:

interface GigabitEthernet0/0/0
 ip address 192.168.1.2 255.255.255.252
 ip ospf network point-to-point
 ip ospf priority 1
 ip ospf 2 area 0

interface GigabitEthernet0/0/1
 ip address 192.168.2.1 255.255.255.252
 ip ospf network point-to-point
 ip ospf priority 1
 ip ospf 3 area 1

Router#sh ip os ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.1.1       0   FULL/  -        00:00:36    192.168.1.1     GigabitEthernet0/0/0
192.162.2.2       0   FULL/  -        00:00:33    192.168.2.2     GigabitEthernet0/0/1

R3:

interface GigabitEthernet0/0/0
 ip address 192.168.2.2 255.255.255.252
 ip ospf network point-to-point
 ip ospf priority 1
 ip ospf 4 area 1

Router#sh ip os ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.1.2       0   FULL/  -        00:00:37    192.168.1.2     GigabitEthernet0/0/0

[Joseph W. Doherty]

it does not form adjacency between router R1

Area 0 and R3 Area 1.

Perhaps what you mean by

adjacency

is not what is an OSPF adjacency.

If you interconnect routers R1 and R3, they will never form an adjacency as, again, neighboring OSPF routers must be within the same area.

If you mean R1 does not "see" R3, nor the converse, also again, that's because they are not in the same OSPF

topology

(if using different OSPF process numbers on R2).

What you're doing on R2 has about the same effect if R2 has all the OSPF interfaces with the same OSPF process number, but you had R1

<area 1> R2 <area 2> R3. 

I.e. R1 would form an adjacency with R2 and R2 would also form an adjacency with R3, but again, R1 would not "see" R3 nor the converse.

[Joseph W. Doherty]

The more I think about your postings, I suspect you don't fully understand the significance of different OSPF process numbers on the same router.

What your doing is basically the same as:

R1 <routing protocol, e.g. RIP> R2 <routing protocol, e.g. BGP> R3

Your two routing protocols can be OSPF.

BTW, you can do redistribution between the routing protocols on R2 and if you do so while using OSPF as one or both of your routing protocols, R2 would become an ASBR.

I'll also note, if you changed all the OSPF areas across the 3 routers to be the same area, R1 would still not "see" R3 or the converse.

[MHM Cisco World]

There are two words here 

Establish ospf ( can happened between two different ospf process but must same area Id)

And advertise route ( route learn from one ospf process not by default inject to second opsf process even if both process in same router here you need redistrubte)

[M.Sultan]

assume R2 has two interfaces in two area,

 area 0

and the otherside in

area 1,

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

Ex : R2 

Process-id 20 for interface connected to area 0

Process-id 40 for interface connected to area 1

If you doubt try it.