Chapter 13. Working with Border Gateway Protocol (BGP)
While interconnecting the routers in your own network is certainly an accomplishment, having your own network without any conduit to the rest of the world is kind of like living on a deserted island. If you want any kind of contact with the rest of the networking world, you need to have some way to talk to people on the mainland. That connectivity between your network island and the mainland Internet is typically provided via the Border Gateway Protocol (BGP).
In this chapter, we introduce you to BGP, describe why and how it is used, and how you can configure and tailor it to suit your specific network's needs.
An Island of Their Own: Autonomous Systems
Interior Gateway Protocols like OSPF and IS-IS enable you to set up networks and exchange routing information within your network. These IGPs let you create your own network island, which you can interconnect so that they can exchange information.
Because these island networks are fully functioning networks, they are, as such, completely autonomous. Given their autonomy, such networks have been aptly labeled Autonomous Systems (AS). An AS is a set of routers and devices, or even a set of networks, that are all controlled by a single entity.
Because they're all operated by a single entity, these ASs can freely exchange information amongst all the routers within. They can allocate addresses with full knowledge of the rest of the network. Security is important, but less than usual because ...