BGP

Chapter 6. Traffic Engineering

Being multihomed means you have two (or more) routes to any destination connected to the Internet. In other words, you need a way to decide which route is better. When left to its own devices, a BGP router will try to send traffic over the route with the shortest AS path. Depending on the connectivity of your upstream ISPs and traffic patterns, this will suit the available bandwidth of the respective connections to varying degrees. Even though bandwidth is getting cheaper all the time, it’s usually advantageous to try to balance the traffic so that it takes advantage of all the available bandwidth in a multihomed setup. Thus, if BGP decides that most of the outgoing traffic should go through the smallest pipe, you will have to tell it that this isn’t what you want by tweaking one or more BGP attributes. Ideally, more traffic will then flow over the under-used connection. At the same time, you’ll want the traffic to take the best route to a destination, if possible, whatever “best” may be. This type of activity is called traffic engineering.

Engineering outgoing traffic is the easy part, because you have control over what your own routers do. It’s harder to get incoming traffic balanced properly over the available connections. At the end of the chapter, there is a discussion of queuing, traffic shaping, and traffic policing techniques that can be used to maximize network performance under low-bandwidth conditions.

The examples in this chapter all assume ...