Automating the iBGP organization in large IP networks

For years, the Border Gateway Protocol has been used as the interdomain routing protocol inside the Internet [9]. This protocol allows ASes to exchange routes to reachable destinations. A BGP route contains, among other attributes, the list of ASes that form a path to the destination, i.e. an IP prefix. This list is called an AS Path. Thanks to the BGP routes it receives, an AS has all the information needed to forward packets towards their destination by sending them to the best BGP nexthop in the first AS in the AS Path. In practice, there are several BGP routers inside an AS. The routes from a neighbouring AS are received by the routers that have a peering session with this neighboring AS. Such sessions are called eBGP sessions. However, other routers that do not have a peering session with this particular neighbour also need to receive this information. For this purpose, routers inside an AS establish internal BGP sessions, called iBGP sessions.