Learn route via ospf rather than ebgp

acbenny · ‎07-22-2008

Hi all,

It is strange that I don't know why the 26 router will learn below network via ospf

method, I think it should be learned via 17A ebgp Router (192.168.1.2). Anyone know

what happen on it ? Thank you

O E2 202.122.65.192 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 202.122.65.128 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 202.122.65.64 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 202.122.65.0 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 172.20.1.0 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 172.20.1.4 [110/1] via 10.1.1.3, 00:12:16, Ethernet0/1

O E2 192.168.170.192 [110/1] via 10.1.1.3, 00:12:21, Ethernet0/1

O E2 192.168.170.128 [110/1] via 10.1.1.3, 00:12:21, Ethernet0/1

O E2 192.168.170.64 [110/1] via 10.1.1.3, 00:12:16, Ethernet0/1

O E2 192.168.170.0 [110/1] via 10.1.1.3, 00:12:16, Ethernet0

O E2 192.168.169.192 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 192.168.169.128 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 192.168.169.64 [110/1] via 10.1.1.3, 00:12:15, Ethernet0/1

O E2 192.168.169.0 [110/1] via 10.1.1.3, 00:12:16, Ethernet0/1

Edison Ortiz · ‎07-22-2008

Please take a moment and memorize the "BGP Best Path Algorithm" :)

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml

What does step 2 says?

What did you do on router 36 that alter a default BGP configuration?

Did you see the BGP routes in show ip bgp on router 26 have RIB failure?

What conditions cause a RIB Failure?

Did you also see what router is selected as the best route on that table?

The best route is eBGP or iBGP?

What's the AD for iBGP?

I'm sure, you will get your answer after drilling these questions, fun? :)

___

Edison.

sdoremus33 · ‎07-22-2008

As previously mentioned rtr26 and 36 are the exit points for 16a in the same AS (IBGP), The Local Pref attribute is used by IBGP peers to set a preferred exit point out of an AS. The way it works is the router with the highest local pref winds and therefore becomes the preffered route.So basically if you set the local pref to higher value at rtr26 it becaomes the preffered path

Try this show ip route 202.122.65.0 and check out the routing output

gojericho0 · ‎07-22-2008

Also when you have multiple redistribution like you do, make sure you watch your administrative distances. This would also be a cause of suboptimal routing in a situation like this without a mechanism to block routing updates