Hello,
what you can do is to insert one default route from each internet gateway. Depending on the metric and type of external route created you will even achieve load sharing or primary/backup scenarios.
In any case you will only need one area 0 (backbone area). In fact OSPF doesn´t operate properly, if you have two disconnected backbone areas.
An example config for your case could look like this:
ISPgw1 (primary):
interface Serial0
description to ISP1
ip address 10.1.1.2 255.255.255.252
ip route 0.0.0.0 0.0.0.0 Serial0
!
router ospf 10
default-information originate
ISPgw2 (backup):
interface Serial0
description to ISP2
ip address 10.2.2.2 255.255.255.252
ip route 0.0.0.0 0.0.0.0 Serial0 250
!
router ospf 10
default-information originate
The administrative distance on the static default to ISP2 makes sure, that it will not be in the IP routing table as long as the primary router ISPgw1 announces the default through OSPF. And as ISPgw2 has no static default route it will not announce a default itself. Once ISPgw1 withdraws the default route, because Serial0 is down, the static default on ISPgw2 will be insertad into the routing table and therefore ISPgw2 will announce a default through OSPF.
This is a primary/backup case. By not configuring the AD of 250 on the static default in ISPgw2 you can achieve load sharing.
Hope this helps! Please rate all posts.
Regards, Martin
