[OSPF]Any preference for higher cost Intra-Area route over Inter-Area route

Unanswered Question
Nov 18th, 2007

If there is a intra-area route to a network that cost more than the inter-area route, is there a preference to choose the higher cost intra-area route over the lower cost inter-area route?

Eg.

Router1(f0/1)-----Area 1-------(f0/0)Router3

|(f0/0)

|

|Area 1

|

|(f0/0)

Router2(f0/1)-----Area 2------(f0/1)Router3

* The Router3 shown above refers to the same router.

Router1 f0/0 and f0/1 are in Area 1.

Router2 f0/0 is in Area 1.

Router2 f0/1 is in Area 2.

Router3 f0/0 is in Area 1.

Router3 f0/1 is in Area 2.

From Router2, to reach f0/0 (Area 1) of Router3, the route will go from Router2->Router1->Router3. Why doesn't it take the shorter path from Router2 to Router3? Is it because the longer route is in the same area and hence is preferred over the shorter inter-area route?

Thanks.

I have this problem too.
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bvsnarayana03 Sun, 11/18/2007 - 06:17

In case of OSPF routes, the order of

preference is: (highest to lowest)

Intra area

Inter area

External route type 1 (E1)

External route type 2 (E2)

Within a single ospf process, u cant force the routes to change their preference. This may be possible for routes from different ospf processes.

pls rate if helped.

JORGE RODRIGUEZ Sun, 11/18/2007 - 06:19

David, not expert in OSPF but there is rule described in RFC-2328 for OSPF route preference, bellow is the order, Intra-area routers are preference over interarea routes

1-intra-area routes, O

2-interarea routes, O IA

3-external routes type 1, O E1

4-external routes type 2, O E2

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094704.shtml#q13

HTH

jorge

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