A loop-free routing protocol for large-scale internets using distance vectors

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The loop-free path-finding algorithm (LPA) has been shown to maintain loop-free routing tables and to obtain correct routing tables after topological and link-cost changes faster and with less processing and communication overhead than link-state algorithms and prior loop-free routing algorithms based on vectors of distances. The limitation of LPA and prior routing algorithms based on routing trees has been the fact that, because LPA operates by communicating shortest-path routing trees incrementally among neighbor nodes, it forces routers to maintain more ‘host routes’ than would be needed in a traditional distance vector algorithm. Maintaining such information incurs additional storage overhead and may not be feasible in some cases (e.g. due to subnetting). To remedy this, and to provide a scalable Internet routing solution, we propose a new hierarchical routing algorithm that combines LPA with the area-based hierarchical routing scheme first proposed by McQuillan for distance-vector algorithms. The new algorithm, which we call the hierarchical information path-based routing (HIPR) algorithm, accommodates an arbitrary number of aggregation levels and can be viewed as a distributed version of Dijkstra's algorithm running over a hierarchical graph. HIPR is verified to be loop-free and correct. Simulations are used to show that HIPR is much more efficient than OSPF in terms of speed, communication and processing overhead required to converge to correct routing tables. HIPR constitutes the basis for future Internet routing protocols that are as simple as RIPv2, but with no looping and better performance than protocols based on link-states.