BGP Routing Issue

[rmnr]

Hello,

We have started facing this issue recently where our Public IP Address with AT&T cannot be accessed by anyone especially for people using Comcast Internet.

We have two core routers with iBGP configured, please refer below topology:

So the issue is only with the IP Address we use that is owned by AT&T(Router1). These IP Addresses are only routable via AT&T. We do not advertise this on BGP. Lets take 200.200.200.2 as AT&T Owned IP. 

This IP Address is not reachable via any Routes that has the best path via Comcast(Router2). When someone from Comcast internet access this site, we see the traffic coming inside, but when the reply goes, it will go to AT&T Router1 and from there it is send to the Comcast Router2. Making it no routable to the end user.

Is there anyway that we can get this fixed without killing the BGP loadbalancing?

Thanks,

Rijath Mohammed

[Richard Burts]

Rijath

What is it that makes it unroutable to the end user if the response is sent to router 2? Without understanding what is the basic problem we are not able to make good suggestions for you.

HTH

Rick

[rmnr]

Thank you for Replying, Rick.

Actually that is the part that I am having trouble with understanding. We know the packets are being pushed to router 2 but not sure why they are not reaching to an end user.

Thanks,

Rijath Mohammed

[Richard Burts]

Rijath

If that is not clear then please post the config of both routers and also the output of show ip route from router 2.

HTH

Rick

[Philip D'Ath]

Is the NAT being done by an ASA? If so, you will probably have to put both of the interfaces into the same traffiic zone to allow asymmetric traffic flows.

[Julio E. Moisa]

Hi

Im not sure if Im understanding the question properly, but please correct me, Have you verified the metrics on Router 1 why the packets are taking the path Router 1 -- > Router 2 --- > End User instead go directly throug AT&T path?

Probably AT&T has a restriction on their peer. You could provide a show ip bgp <ip address> on Router 1?

Thanks