BGP help required

[Rizwan Khan]

Hi i need assistance in configuring BGP miltihoming with dual ISPs and 2 routers.

I am telling the actual scenario in which we are running right now. We have 2 ISPs Internap and XO, we are getting default routes from both of them via ebgp. Internap is set as default path for outgoing traffic as its preference is advertised with high local preference to other(XO) router via ibgp.We have 3 subnets which we want to advertise to the outside world. 216.0, 217.0, 218.0. We have advertised to outside world that 217.0 and 218.0 are reachible efficiently through INternap and 216.0 through XO by appending AS paths. so that we can do load sharing. The scenario is working fine. The issue comes for incomming traffic for 216.0 network. it chose XO as its path but response back is still going through Internap as its local preference is high for default routes. I want that response for 216.0 should also go back from Xo router. Please help me out with this setup ill be very thhankful. Besides we have only 2 interfaces on our routers.

[pgurumu77]

One way of solving it is my using policy routing, if my destination is 216, then next-hop is XO.

[Harold Ritter · Accepted solution]

Hi Rizwan,

The as-path prepend does not always work. One way to garantee that traffic to 216.0 will alway be preferred via XO is to advertise 216.0/24 via XO as you currently do and advertise 216.0/23 (includes 216.0/24 and 217.0/24) and 218.0/24 via Internap. The more specific 216.0 advertised via XO will always be preferred no matter what.

Regards

[Rizwan Khan]

Thank you Harold for a very nice suggestion. really appreciate it.