06-18-2012 07:29 AM - edited 03-04-2019 04:42 PM
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
06-18-2012 07:44 AM
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
06-18-2012 07:52 AM
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
06-18-2012 07:56 AM
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
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