Friday, January 2, 2009

OSPF Routing Problem

Consider the following scenario.

Router 1 is sending a lot of traffic to the subnet on Router 2. The preferred route (by default) is via R3 as this is an Intra-Area Route. The route between R1 and R2 is an Inter Area route so will NOT be considered for the traffic flow - this is regardless of the metric cost value.

The question is how to get R1 to prefer the direct, faster route to R2! As mentioned altering the route cost will have NO bearing, as Intra vs Inter are considered above such comparisons. Intra Area routes always win regardless of costs.

The way around this problem is to build a virtual link between R1 and R2. This way once up, the route to will beomce preferrable.

Router 4
router ospf 100
area 1 virtual-link 5

Router 5
router ospf 100
area 1 vitual-link

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