Admin distance on ASBR

Answered Question
Mar 11th, 2010

Hi,

Trying to adjust admin distance of external routes injected in OSPF domain from eigrp :

router ospf  10

redistribute eigrp 11 subnets

distance 200 0.0.0.0 255.255.255.255 eig-to-ospf

ip access-list standard eig-to-ospf

permit ip 10.1.1.0 0.0.0.255

permit ip 10.1.2.0 0.0.0.255

in ip routing table of ASBR

10.1.1.0 /24 and 10.1.2.0 /24  are learned from EIGRP process.

But in OSPF domain these routes are not being injected with admin distance as 200. But those are getting same ospf 110 admin distance.

Please share the experince

Thanks

Subodh

I have this problem too.
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Correct Answer by Giuseppe Larosa about 6 years 9 months ago

Hello Subodth,

AD cannot travel from node to node and it is never part of a routing protocol update.

your configurations apply to local node only, but as you have seen the routes are learned by EIGRP, and so you will never see those routes with admin 200 until the EIGRP neighborship is up.

This is a safety measure to ensure that if EIGRP neighborship fails and later it is restored the local node will accept as best routes for the IP subnets specified in the ACL those coming from EIGRP rather then OSPF routes that are the result of redistribution of EIGRP into OSPF in another ASBR node (if any).

Other OSPF routers can choice between different OSPF external routes (LSA type 5) based on metric type, seed metric and OSPF cost to ASBR node.

O E1 are preferred over O E2 regardless of seed metric.

O E2 keeps separated costs for route and for path to ASBR

O E1 routes sum seed metric and OSPF cost to ASBR.

Use of O E1 is recommended when you have multiple ASBR nodes.

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Fri, 03/12/2010 - 03:21

Hello Subodth,

AD cannot travel from node to node and it is never part of a routing protocol update.

your configurations apply to local node only, but as you have seen the routes are learned by EIGRP, and so you will never see those routes with admin 200 until the EIGRP neighborship is up.

This is a safety measure to ensure that if EIGRP neighborship fails and later it is restored the local node will accept as best routes for the IP subnets specified in the ACL those coming from EIGRP rather then OSPF routes that are the result of redistribution of EIGRP into OSPF in another ASBR node (if any).

Other OSPF routers can choice between different OSPF external routes (LSA type 5) based on metric type, seed metric and OSPF cost to ASBR node.

O E1 are preferred over O E2 regardless of seed metric.

O E2 keeps separated costs for route and for path to ASBR

O E1 routes sum seed metric and OSPF cost to ASBR.

Use of O E1 is recommended when you have multiple ASBR nodes.

Hope to help

Giuseppe

bapatsubodh Fri, 03/12/2010 - 06:00

Hi,

Thanks a lot.

" AD cannot travel from node to node and it is never part of a routing protocol update" .

So it affects only on the router on which it is configured.

Using metric-type as 1 and setting up the seed cost will be a very simple solution.

Thanks

subodh

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