Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

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

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.

2 REPLIES

Re: [OSPF]Any preference for higher cost Intra-Area route over I

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.

Re: [OSPF]Any preference for higher cost Intra-Area route over I

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

912
Views
10
Helpful
2
Replies