OSPF E2 type route

Answered Question

I am a bit confused with the ospf type E2 route. As per the doc when a route is marked as type E2, it does not calculate the metric to the ASBR



Then referring to the attached diagram, why isn't that iam seeing 2 routes for the subnet 1.1.1.0/24 and the drfault 0.0.0.0


R2 and R4 have been configured with default-information originate command

At R3 I see only one default route from R2.


Ambi



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Correct Answer by Edison Ortiz about 9 years 3 months ago

Ambi,


What you are seeing is called recursive-routing. In order for R3 to know about routes from R4, the cost is 2 from R3 (see show ip route)

O 20.20.20.4 [110/2] via 30.30.30.2


while in order for R3 to know about routes from R2, the cost is 1 - the cost of the fastethernet interface.


Increasing the cost on the fastethernet interface on R3 that is facing R2 (ip ospf cost 2) should provide the desired result.


HTH,


__


Edison.

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Edison Ortiz Sun, 02/10/2008 - 07:22
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Can you post the show ip ospf database from R3 ?


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Edison.


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Edison Ortiz Sun, 02/10/2008 - 09:16
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Ambi,


What you are seeing is called recursive-routing. In order for R3 to know about routes from R4, the cost is 2 from R3 (see show ip route)

O 20.20.20.4 [110/2] via 30.30.30.2


while in order for R3 to know about routes from R2, the cost is 1 - the cost of the fastethernet interface.


Increasing the cost on the fastethernet interface on R3 that is facing R2 (ip ospf cost 2) should provide the desired result.


HTH,


__


Edison.

Edison Ortiz Sun, 02/10/2008 - 09:54
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> Increasing the cost on the fastethernet interface on R3 that is facing R2 (ip ospf cost 2) should provide the desired

> result.


Looking back, I'm not 100% sure about this statement as R3 sees R2 via connected so OSPF does not play a part of the cost here. Please test and let me know.


__


Edison.

royalblues Mon, 02/11/2008 - 00:04
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Edison is absolutely correct that the behavior is due to recursive routing.


I managed to lab the setup and it works


you should see the two routes in the rotuing table as required if you increase the ospf cost to 2 between R2 and R3


HTH

Narayan

s.arunkumar Mon, 02/11/2008 - 00:43
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Hi

Nice topic.. :)


To add to edison point

"If the external routes are both type 2 routes and the external costs to the destination network are equal, then the path with the lowest cost to the ASBR is selected as the best path.""


REF:: http://www.cisco.com/warp/public/104/1.html#t32


arun

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