Frequently Asked Questions

Q— I am not running IBGP between my border routers. Do I need to worry about routing loops?

A— As far as the interaction between IGP and BGP, loops cannot occur. If your internal routers are following a default toward the BGP border routers, after the traffic reaches the border router, it has only one way out via the EBGP session.

Q— I have two BGP border routers running IBGP and connected via a serial link. I am using local preference to control my exit points. What happens if the serial line goes down?

A— If you are setting BGP policies that cause traffic to be directed between BGP border routers, this would be the same scenario as if you did not have a link between the border routers. While the serial line is down, your traffic might end up looping inside the AS.

Q— If I use a serial link between my IBGP border routers to direct traffic from one router to the other, should that link be as fast as my links to my providers?

A— The only traffic that line will carry is outbound traffic that is redirected between border routers and a portion of incoming traffic. Try to figure out what percentage of your total traffic that constitutes to estimate the appropriate link bandwidth.

Q— I need to direct traffic toward destination X over my serial line and toward destination Y over my Ethernet line. Can I do that via policy routing?

A— What you have just described can be done via static routing, which works based on destination. There is no need for policy routing, which works based on source or source and destination combined.

Q— Do I apply policy routing over my outbound or inbound router interface?

A— Policy routing checks source addresses coming into an interface. Configure on the inbound interface.