Ericsson Nominum China Mobile China Mobile This document describes an abstract API that provides the minimal functionality required for a program to communicate effectively with peers and services on the network while running on a host that has more than one active network interface. This API is abstract: we describe the functionality that must be provided, not the bindings that should be used to provide that functionality. The functionality described here provides the building blocks from which higher-level APIs might be built, and is not intended to be used directly by typical applications.