Internet Core Protocols: The Definitive Guide

Route aggregation

New address assignment schemes are being deployed that allow routes to be aggregated together. Now, when you request a block of Internet addresses from your Internet Service Provider, the ISP must assign one from a larger block that has already been assigned to them. This allows routing to happen at a much higher level. Rather than ISPs having to track and advertise thousands of network routes, they only have to advertise a few super-routes.

The ISP will still have to track all of the networks that are under it, but it won’t have to advertise them to other ISPs. This feature cuts down on the amount of backbone router-update traffic immensely, without losing any functionality.

Geography-based aggregation schemes are also being deployed. For example, any network that begins with 194 is somewhere in Europe. This simple assignment allows major routers on the Internet to simply forward traffic for any network that begins with 194 to the backbone routers in Europe. Those routers will then forward the datagrams to the appropriate regional ISP, who will then relay the datagrams on to their final destination.

This process is conceptually similar to the way that area codes and prefixes help the phone company route a call. Telephone switches can route a long-distance call simply by examining the area code. The main switches in the remote area code will then examine the telephone number’s three-digit prefix, and route the call to the appropriate central office. By the time ...