Source-specific routing (not to be confused with source routing) is a routing technique where routing decisions depend on both the source and the destination address of a packet. Source-specific routing solves some difficult problems related to multihoming, notably in edge networks, and is therefore a useful addition to the multihoming toolbox. In this paper, we describe the semantics of source-specific packet forwarding, and describe the design and implementation of a source-specific extension to the Babel routing protocol as well as its implementation - to our knowledge, the first complete implementation of a source-specific dynamic routing protocol -, including a disambiguation algorithm that makes our implementation work over widely available networking APIs. We further discuss interoperability between ordinary next-hop and source-specific dynamic routing protocols. Our implementation has seen a moderate amount of deployment, notably as a testbed for the IETF Homenet working group.

While game semantics has been remarkably successful at modelling, often in a fully abstract manner a wide range of features of programming languages, there has to date been no attempt at applying it to subtyping. We show how the simple device of explicitly introducing error values in the syntax of the calculus leads to a notion of subtyping for game semantics. We construct an interpretation of a simple /spl lambda/-calculus with subtyping and show how the range of the interpretation of types is a complete lattice, thus yielding an interpretation of bounded quantification.