OSPF adjacency between non-default areas

[Mohamed Abdul Rezak]

Hi Experts,

This question is slightly different

The topology  is like this with all ethernet links

R1<---Area0--->R2<---Area1-->R3<---Area2--->R4

When I check the neighborship of R3 and R4  , the neighborship is fine

R3#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface

10.1.1.2          1   FULL/DR         00:00:33    20.1.1.1        Ethernet1/1

30.1.1.2          1   FULL/DR         00:00:38    30.1.1.2        Ethernet1/0

R3#

In R4 also the neighborship is fine

R4#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface

20.1.1.2          1   FULL/BDR        00:00:35    30.1.1.1        Ethernet1/0

R4#

If the neigborship is fine , why are the routes not being exchanged ?

R4 routing table  contains only the directly connected routes .

PS: I know about the A0 and the normal ospf design, i just want to know why this does not work .

Thanks

Mohamed

[John Blakley]

Mohamed,

In this type of setup, you'll need to configure a virtual link between R2 and R3 to extend area 0. All areas need to physically connect to area 0 in order to have all routes passed to all areas. If there is a non-backbone area between area 0 and the other area, a virtual link is required.

To create it, on R2 and R3 you'd do:

On R2:

area 1 virtual-link

On R3:

area 1 virtual-link

You'll see the routes you need on R4 after doing this.

HTH,

John

[Mohamed Abdul Rezak]

Hi John,

Thanks for the reply, but this is not what exactly I am looking for

I know about VLs.

I want to know why we need VLs when the neighborship is established (FULL state - which means DBD packets have been exchanged and  loaded )

Mohamed

[Elvin Arias]

The routes are not being exchange becuase you basically broke the normal OSPF design requirements, so you will need a virtual-link in order to interchange the routes. You need a virtual-link because technically only an ABR can exchange routes between areas, and what an ABR is? A router that connects between area 0 and other non-transit area.

Elvin