[c-nsp] Help with unique BGP setup

[Zoe O'Connell]

Lobo wrote:
> We're trying to do a custom bgp setup for one of our customers but I'm
> not sure if it's even possible with IOS.  Our network has its primary
> upstream connection in a different city from where this customer will
> connect.  However each city has its own local internet connection as
> well for backup purposes.  The market that this bgp customer is to be
> turned up on uses the local isp connection as its primary due to
> capacity issues on the intercity going back to the core city.
>
> This customer's requirements for bandwidth can be met if they use the
> local connection only but should the connection go down, they would
> most likely saturate the intercity connection and impact everyone
> else.  What has been proposed is that they will use the local
> connection to get internet access and should this access go down, they
> want the bgp session to be dropped or something equivalent that will
> make sure they don't go over the intercity.
>
> To my knowledge I know of no configuration that can drop a bgp session
> based on some next hop attribute.  Is there some way to control this
> customer's traffic as stated above?  Any examples you guys can offer?

Do you actually need to drop the session, or is it sufficient to
advertise zero prefixes? If the latter, you could apply a route-map
outbound towards the customer that only allows the "local" internet
routes to be advertised to them, by setting/matching communities
appropriately. For example:

route-map transit-in permit 10
 set community YOURAS:1234

ip community-list standard LOCAL-ROUTES permit YOURAS:1234

route-map customer-out permit 10
 match community LOCAL-ROUTES

Similar can be applied in reverse to prevent the customer's routes being
advertised out transit links other than the local one.