OSPF Area 0 routing

[dhcchan]

Hi there,

I have four routers, Cisco 3745-1, Cisco 3745-2, Cat 4506-1 and Cat 4506-2. Cat 4506-1 and Cat4506-2 connect together via dot1q trunking for Vlan 1 and Vlan 2 as ospf area 1. The Cat 4506-1 Vlan 3 is configured with area 0, which connects to the Cisco 3745-1. While the Cat 4506-2 Vlan 4 is configured with area 0, which connects to the CIsco 3745-2. The two Cisco 3745-1 and Cisco 3745-2 are backone router with all interfaces as area 0. There is a WAN link (interface S0/0) configured at both of the Cisco 3745 routers connecting to HQ.

I have found when the Cisco 3745-1 s0/0 is unplugged, the Cat 4506-1 cannot learn HQ routes from Cat 4506-2 via vlan 1 or vlan 2(area 1).

But I find some more findings at the time as below:

1. The Cat 4506-2 can learn HQ routes from Cisco 3745-2 router.

2. The OSPF neighbor relation between Cat 4506-1 and Cat 4506-2 are full.

3. The relation between Cat 4506-1 and Cisco 3745-1 is full as well.

May I ask that is it normal for the Cat 4506-1 cannot learn other area routes via area 1, with the same time that the area 0 neighbor is still alive?

Also, may I ask that if the Cat 4506-1 area 0 neighbor die, can it learn other area routes via area 1?

thanks a lot

David

[DWAM_2]

Hello,

Are 3745-1 and 3745-2 connected together ?

When you are an area 0, the backbone area can not be discontinuous if not you will have problem.

When you have the cable s0/0 unplugged, your backbone is discontinuous (isn't it?), and the relation between 4506-1 anbd Cisco3745-1 stay full.

Perhaps it's something like that.

Good luck.

[ERIK LAWAETZ]

As already stated you're suffering from a discontinuous area 0.

In your design you can solve it in 2 (3) ways:

- create a vlan between the 4506s in area 0 so area 0 remains continuous.

- make the links between the 3745s and 4506s part of area 1.

- (create a virtual link thru' area 1, but virtual links should generally be avoided).