PSP: Path state protocol for inter-domain routing

Link-state routing protocols are known to be robust and to support shortest paths routing, but they do not support policy-based routing and suffer from scalability problems. Therefore, traditionally, link state protocols are used for intra-domain routing while path (or distance) vector protocols, such as BGP, are used for inter-domain routing where policies and scale are dominant. In this paper we present PSP, a path state protocol for policy-based inter-domain, routing for a network of Autonomous Systems (ASes) such as the Internet. A path state protocol is an extended link-state routing protocol that enables both link-states and path-states advertisements (of path costs). PSP supports policy-based routing similar to BGP and takes into account the Internet-like policies that are based on business relations between ASes. PSP can run on arbitrary multi-region (i.e., hierarchies, areas) networks which reduce global traffic and improve scalability. We provide two versions of the protocol: SLP (Shortest Legal Paths) that guarantees forwarding of messages along the policy-based shortest path and SCLP (Shortest Costumer-preferred Legal Paths) which is easier to implement in a network. We prove the correctness of both algorithms and provide various performance measurements on a real ASes network.