Efficient routing using NIx-Vectors

Abstract

We introduce the concept of Neighbor-Index Vector (NIx-Vector) routing which gives efficient and consistent routing of packets in Internet routers. A NIx-Vector is a compact representation of a routing path, which is small enough to be included in a packet header. We show how, by including the routing information in the packet header, routing decisions can be made in O(1) time at each router, with no caching or state in the routers (other than the existing routing tables). The creation of a NIx-Vector for a source and destination pair requires one round trip time, but once the NIx-Vector is known, it can be retained by the source and reused indefinitely with no further setup time required (or until it becomes no longer valid, which is easily detected). In addition to O(1) routing decisions, the use of NIx-Vectors to record and specify routes has other benefits. NIx-Vectors provide for route pinning which is beneficial for reservation protocols and mitigates the effect of routing flaps on long lived flows. A variation of NIx-Vectors can insure symmetrical routes from a source to a destination and back to the source, which is also beneficial to some reservation protocols. We give a complete description of how NIx-Vectors are created and used in Internet routers; and give empirical data showing the number of bits required to represent NIx-Vectors for typical Internet paths.