1. A method for using a network device having an operating system instance that operates in a plurality of routing contexts, the method comprising: associating a first network with a first routing context and a second network with a second routing context, wherein the first context is isolated from the second context; enabling a first application running on the operating system instance of the network device to select the first routing context by associating the first application with a first routing context number; enabling a second application running on the operating system instance of the network device to select the second routing context by associating the second application with a second routing context number; receiving, at the same networking address of the network device, a first message originating from the first network and a second message originating from the second network by the network device; at a packet ingress processing module in the network device, assigning to the first message either the first routing context number or the second routing context number based on one of a source network interface and a source application socket; and providing heritability of the first routing context number, wherein the heritability assigns to a child application of the first application a default routing context associated with the first routing context.