Up to now, our discussion has focused solely on routing protocols that operate within a single organization, or, as it would be called in the world of networking, single autonomous systems (AS). Routing protocols that operate within a single AS are referred to as interior gateway protocols (IGPs). But what about traffic that leaves the AS what happens to it? The answer to that is exterior gateway protocols (EGPs). Just as IGPs operate solely within a single AS, EGPs operate between ASs, providing connectivity between organizations rather than within them.

The most well-known and by far widely deployed EGP is BGPv4. For purposes of this discussion we will just refer to it as BGP. Entire books have been written on this protocol for two basic reasons: First, it is a very complex and intricate protocol, and very few people are actually proficient in their understanding of this protocol, and second, because it is one of the most important protocols in use today, connecting the ASs of the world. With this in mind, it would be impossible to have a detailed discussion of this protocol within this chapter, so we are briefly going to discuss some of the basic concepts behind this protocol and then turn our attention to the specific IPv6 configuration tasks and considerations.