Strange problem with EIGRP and BGP

[bgibson]

I have a router that is running both eBGP and EIGRP. EBGP out to one of my wan clouds and EIGRP into the core.

I am redistributing BGP into EIGRP and EIGRP into BGP. I know this isn't ideal but it is necessary for the moment.

The problem I am having is that I need this router to prefer the BGP route over the EIGRP learned route which comes through our other WAN cloud.

As I understand it the router SHOULD select the eBGP route since the administrative distance is 20 for eBGP learned routes. But for some reason it is using the EIGRP learned routes with an administrative distance of 90.

I can "fix" this by changing the administrative distance of EIGRP on the router to 200. But I shouldn't need to do this. When I make this "fix" the bgp route is selected and it has an admin distance of 20.

I don't get it.

Note: I did have the BGP distances changed earlier but I removed that command and clear the route tables and BGP process.

Any ideas?

[royalblues]

Yes friend,

The best way is to use network statements in BGP which alleviates this problem. But this May depend on the number of prefixes you have.

We use the same technique in our network

HTH, rate if it does

Narayan

[jbrunner007]

Sundar, You are correct!

after I cleared the EIGRP neighbor,

BGP is preferred...

fr_hub#sh ip route

Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is 10.230.13.1 to network 0.0.0.0

100.0.0.0/32 is subnetted, 1 subnets

C 100.100.100.1 is directly connected, Loopback1

201.1.1.0/30 is subnetted, 1 subnets

C 201.1.1.0 is directly connected, Serial0/0.201

202.2.2.0/30 is subnetted, 1 subnets

C 202.2.2.0 is directly connected, Serial0/0.202

9.0.0.0/24 is subnetted, 1 subnets

B 9.9.9.0 [20/0] via 202.2.2.2, 00:00:04

10.0.0.0/24 is subnetted, 1 subnets

C 10.230.13.0 is directly connected, FastEthernet0/0

S* 0.0.0.0/0 [1/0] via 10.230.13.1

[jpl861]

Hi Guys,

I just have a question here. Yes, the BGP route will be inserted in the routing table after clearing the EIGRP neighbor so the EIGRP route with the AD of 90 will disappear and the eBGP route with the AD of 20 will be injected. After the EIGRP neighbor comes up, and redistribution happens again, the route will be redistributed again to BGP and it will have a route in the BGP table with a weight of 32768. Will the BGP process reset it's best route automatically to the redistributed route with the weight 32768 as the best route?

Of course if this happens, the EIGRP route will be prefered again because the redistributed route will be a locally injected route with the AD of 200 and the EIGRP route with the AD of 90.

And what if the BGP table does not update automatically? The BGP route will stay in the routing table right? Do I need to issue clear ip bgp x.x.x.x to prefer the EIGRP route?

Sorry for bringing up this topic again. :)

-John

[sundar.palaniappan]

John,

First of all this isn't a very common setup where a route is being learned via BGP and an IGP (EIGRP) and is mutually redistributed between both protocols. That right there warrants some extra measures to make sure routing works the way it should.

To answer your question the last part of what you said is true i.e when the router starts using EBGP route it wouldn't replace that with EIGRP route because the EIGRP route wouldn't be redistributed into BGP as it would only exist in the EIGRP topology table and not in the routing table. Clearing BGP neighbor will very likely cause the EIGRP route to take over.

HTH

Sundar

[jpl861]

Thank you Sundar for replying to my question. So the redistributed route won't appear in the BGP table unless you clear it. You mentioned that clearing the BGP neighbor will very like cause the EIGRP route to take over. Can I just clear the route in the BGP table for example clear ip bgp 9.0.0.0/24 to inject the EIGRP redistributed route in the BGP table?

-John

[rohan.jhaveri]

The router would prefer any route over a redistributed route rrespective of the administrative distance.The eBGP route that router sees might be a redistributed one.The output of your routingtable will hellp troubleshoot the same.