IBGP without IGP problem.

[rnikhan77]

Ii am stuck in a very simple BGP topology. In below topology m not using any IGP. AS 100 is a transit path for AS 200 and AS 300. All the routers in AS 100 is fully meshed IBGP with synchronization off. As the task says we cannot use next-hop-self command. As far as i know i have done all configs properly but still R1 is not receiving the loopback of R5 and same for R5. Also the IBGP neighborship between R1 and R5 is flapping. Some one told me its a GNS3 issue. Can you guys pls go through the topology once to check is anything wrong in it.
Configs :

[shillings]

Can each router ping its neighbor's loopback? I presume R1 and R5 are OK, but worth checking the rest.

[cadet alain]

Hi,

in your AS 100 you need a  static route on R2 and R4 for each BGP peer address otherwise they won't form a neighbourship( as seen with show ip bgp summary on both routers, you'll see they only peer with R3)

You also need a static route for each link to the eBGP peers on all routers in AS 100 otherwise you would need next-hop-self on the border routers in AS 100 but you can't use this feature.

Regards

Alain

Don't forget to rate helpful posts.

[rnikhan77]

R2 is forming neighbourship with R4, but its flapping.I know adding a RR or static route will solve the problem. But my issue is that why peering between R2 - R4 is flapping ? Someone told me that R2 is learning the R4 connected route from BGP peering which inturn it uses to form peering. Thats why its flapping. Is it so?

[milan.kulik]

Hi,

yes, I've seen the same behaviour in a lab some years ago.

You need static routes Alain mentioned to make your BGP stable.

BR,

Milan

[ranjithvm]

Hi,

Use route-reflector client command in r3

[milan.kulik]

Hi,

will that work without next-hop-self command?

BR,

Milan

[paul driver]

Hi Milan,

Dont fully mesh AS100 -

so the peering should be - R1 (as200) to R2 (as100) to R3 (as100) to R4 (as100) to R5 (as300)

then configure R2 & R4 as route-reflector clients from R3.

No statics required and that should do it.

res

paul