EIGRP To OSPF Redistribution Question

[borman.bravo]

Hello all, wanted to confirm an EIGRP - OSPF mutual redistribution behavior which I tested in my lab, only question I had is when injecting EIGRP 170 routes (redistributed from another router) into an OSPF process, these injected routes do not appear in the routing table but I do see them in the EIGRP topology table and will only appear in the route table if the OSPF routes dissapear. Are those EIGRP to OSPF routes not appearing because of the OSPF AD of 110 which is better? for some reason I was expecting to see both routes in the table after the redistribution with an AD of 110 since EIGRP routes ARE being injected in OSPF, thank you!

router eigrp 100
 redistribute ospf 1 metric 100000 1 255 1 1500
 network 10.10.101.0 0.0.0.255
 no auto-summary
!
router ospf 1
 router-id 10.10.10.1
 log-adjacency-changes
 redistribute eigrp 100 metric 10000 metric-type 1 subnets tag 10
 network 10.144.0.0 0.0.255.255 area 144

[Masoud Pourshabanian]

Hello,

Are you checking the routing table of the same router you are redistributing?

If you are checking the routing table of the same router, you should see the EIGRP route, not OSPF route. You will see the OSPF route in the next router.

I guess this router receives that injected route from another neighbor as well. Injected route is kind of circulating in the network and coming back from other side. I mean this router receives the injected route from two sides.

If you check sh ip route and check the next hop, you will notice that. And if you check  show ip EIGRP topology, you will see " FD is Inaccessible" for that injected route.

I might be completely wrong. Just based on the guess.

If you share your topology with specifying that route and also the routers you are distributing on, I can see it better.

Masoud

[borman.bravo]

Thanks very much for the input and yes my assumption was correct, same router will not inject EIGRP routes because of the preferred OSPF AD since same routes are already present in the routing table.

[Masoud Pourshabanian]

I just noticed that I did not consider redistribution of OSPF into EIGRP. I considered only EIGRP into OSPF.  If you  just redistribute EIGRP into OSPF, you will see only EIGRP routes. OSPF routes will be seen in the next router. As Jon mentioned, if both routes are present, OSPF will be shown inside the routing table due to the lower AD compared to injected EIGRP routes(170)

Masoud.

[borman.bravo]

All, one more issue I came across and I will explain:

Two routers are OSPF neighbors at remote site: Router-A and Router-B, they are not EIGRP neighbors since they connect to two separate clouds but do have routes to reach the same destination networks.

Both receive EIGRP (170) routes from upstream core routers, they both inject these EIGRP learned routes into their OSPF process. Now, I want Router-A to be the preferred path to reach those EIGRP 170 destination networks but here is the issue:

Router-A will see 170 routes via the upstream core router in the cloud, it will also see a 110 cost route via Router-B so it will choose this path which is not the desired path.

How do I set the preferred path via Router-A? without changing AD of OSPF etc.

Thanks so much for the help!

[Jon Marshall · Accepted solution]

If the routes only appear when the OSPF ones disappear then that suggests they are routes for the same destinations just learnt from different routing protocols.

If so then yes you will only see the EIGRP routes if the OSPF routes disappear.

If the routes are for different destinations then on the router doing the redistribution between EIGRP and OSPF you should see the EIGRP routes are AD 170 and only downstream OSPF routers will then see those routes as OSPF routes with an AD of 110.

What you won't see is the EIGRP routes being shown as OSPF routes with an AD of 110 on the router you are doing the redistribution because you only redistribute routes that are already in the IP routing table.

Jon

[Masoud Pourshabanian]

Hello Jon,

5+ from me.

Masoud