dynamic BGP route failover

[slicerpro]

Our client has two sites connecting to us via eBGP. Both client's sites are connected via eBGP and our two local devices are connected via iBGP. We have a need so that whenever any of the remote site networks are not reachable via one site, then the routing should failover to go via the other site.

What is the BGP configuration to achieve this?

Please refer to the sketch of the setup that I've uploaded.

[Jon Marshall]

I would have thought it would work already.

Presumably the client is advertising their local subnet to the other client site which means each remote network should be advertised to both your 6500's eg.

client site A advertises their /24 direct to your 6500_1 via EBGP but also advertises it to client site B which then advertises it to your 6500_2.

The route advertisement received direct on 6500_1 will have a shorter AS path so will be used by both 6500s unless the direct link goes down then 6500_1 should see a path to that network via 6500_2.

The same logic applies for site B's subnet.

Are you saying this is not currently happening ?

Jon

[Julio E. Moisa]

Hi Slicerpro,

Please correct me If I understading wrong the topology.

You have a client where you are connecting your infrastructure via 2 eBPG peers to its infrastructure, you have and iBGP and the primary path to the client's network is through the site A and the backup is the site B, is that correct?

Well the client should be advertising the same prefixes through both sites to your devices. Could you please provide more details.

There are many ways to create a failover, but I would like to understand your question better.

You could use fall-over under the eBGP peering to fast the peering deactivation once the link is down. 

https://supportforums.cisco.com/document/147341/bgp-neighbor-fall-over%E2%80%9D-command-overview

Or consider BGP dampening, but if you really want to shutdown the peering to prefer the backup link you could consider use an EEM script. 

:-)

[slicerpro]

From our local 6500's, If we loose reachability to a remote net because we can't get in touch with a peer, the failover will happen. However if a remote net becomes unavailable but is still advertised by a peer, the failover will not happen. My contention is that it is that peer that should be configured so that if a remote network that it is advertising to us is no longer reachable, the advertisement should stop and at that point we will learn it from the other peer and the failover will happen accordingly. I have been trying to explain that to the client's engineers but this is not penetrating easily.

Is there else anything we can configure on our side.

[Georg Pauwen]

Hello,

can you post the configurations of both your 6500s ?

As stated in the other posts, what you describe should be happening by default. If your peer is unreachable, you shouldn't get any advertisments from that peer. Why failover is not happening...let's have a look at how you configured the neighbors and the iBGP.