Posts

Showing posts from 2020

OSPF Scenario with two Backbone Areas

Image
In the following topology we have two companies: East Company (routers WR1,WR2,WR3), and West Company (router ER1). Some employees of EastCompany reside on WR3 router of West Company (subnet 192.168.10./24). As we can see between West and East Companies there is an uplink which connects routers WR3 and ER1 with OSPF protocol Area 0. As matter of fact we have very odd scenario with two OSPF Backbone Areas. And one more thing, router ER1 should not maintain/see the routes in Backbone Area 0 of WR1 and WR2 routers but users in East Company should be able to get access to all subnets in West Company.

The approach described violates one of the concepts of OSPF which is that the area 0 backbone should be contiguous. It may work or things may break depending on some details of how it gets implemented. Some of the things that can cause black holing of traffic or other problems can include:

- if you have configured stub areas, the stub area will have a default route pointed to its area 0. Tra…