Checking for optimal egress points in iBGP routing

The border gateway protocol (BGP) is used today by routers of all autonomous systems (AS) in the Internet. BGP is responsible for end-to-end reachability in the Internet. BGP routers have to exchange routes towards about 200,000 prefixes (blocks of IP addresses). Inside each AS, routers are using internal iBGP sessions to exchange their best route with other routers. The objective of an iBGP topology is to redistribute BGP routes inside the whole AS. In large ASs, some BGP routers are used as route reflectors because it reduces the total number of sessions needed for this route redistribution.Checking the correctness of iBGP configuration [1] and detecting potential problems inside the iBGP [2] are particularly difficult when route reflection [3] is used. The scalability of route reflection compared to an iBGP full-mesh comes at the cost of opacity in the choice of the best routes by the routers inside the AS. This opacity induces problems like suboptimal route choices in the IGP cost, deflection and forwarding loops. We propose to check for the optimality of the routes choice in a route reflection graph. We do so without requiring to simulate the complex operations of the BGP protocol. Our check procedure is applied to a tier-1 AS. Our simulations show that a significant fraction of suboptimal path choices may occur, between 10 and 30% in realistic cases.