Source-sensitive routing

Source-sensitive routing is a routing technique where routing decisions are made according to both the source and the destination address of a packet. This is a slight refinement of ordinary next-hop routing, as used in the Global Internet, where packets are routed according to their destination only. Source-sensitive solves a number of difficult problems in multihomed edge networks as well as in the presence of tunnels. This paper describes our experience with the design and implementation of a source-sensitive extension to a distancevector routing protocol (the Babel protocol). First, we define the behaviour of our source-sensitive routers, and show that mixing different behaviours in a single routing domain causes persistent routing loops. We then describe two implementation techniques for source-sensitive routing, and show how source-sensitive routers can interoperate with ordinary next-hop routers in a single routing domain. We conclude with experimental data obtained with our implementation.