BGP Route Learning Issue

[anichatterjee19921]

Hello All,

I have allowed 172.16.0.0/16 subnet in my BGP configuration. I have divided this /16 subnet into multiple /24 Subnets and it has been distributed among SPOKE location. But where as BGP is UP. CE is not able to learn routes of this /24s. PE getting routes of multiple /24 from HUB.

[Leonardo Gama]

Hi,

On the remote PEs, do you see all routes being announced to remote CEs?

Are you using same AS number for all CEs?

Cheers.

[anichatterjee19921]

Hi Leonardo, 

Yes all routes being in announced to other PEs and CEs. And yes all the CEs are using same ASN.

[Leonardo Gama]

Hi,

So I think you need to configure "neighbor x.x.x.x allowas-in 1" on the CEs for the BGP session with PE.

Cheers.

[anichatterjee19921]

Hi, 

I tried the same from CE end, but it's not resolved.

[Leonardo Gama]

Hi,

So you will need to run "debug ip bgp update" on CEs in order to verify what is happening.

Cheers.

[Leonardo Gama]

Hi,

Try to configure on PEs "neighbor x.x.x.x as-override 

Cheers.

[trfinkenstadt]

could you post relevant configuration please?

[paul driver]

Hello

Just to clarify you have multiple ce sites all with cider'ed 172.16.0.0/16 addressing, and these sites cross an mpls layer 3 vpn and are peering with the same ASN to their PE rtrs

How are you adverting each site subnet to the PE ?

Can you post the config of them and the bgp table
sh run | be router
sh ip bgp | B N

res
Paul

[anichatterjee19921]

Hi,

Its a basic hub and spoke topology. CEs are connected through L3 VPN. Though its not a best practice to advertise same /16 from all the PEs. Still it's going on. Now the CEs are advertising /24. Which is subnetted from the same /16. And we are advertising the summarized route. CEs are using same ASN.

[paul driver]

Hello

So your aggregating the /16  -
Have you appended the summary only and as-set attributes to the aggregate - Are you aware all specific prefixes are suppressed when you do this?

can you post:sh ip bgp neighbors x.x.x.x advertised-routes
sh run | be router

res
Paul