Patent ID: 7983239

Claim:
A method preformed by a network device comprising: acquiring information as to the internal topology of a sub-network that uses a private, internal routing system; constructing a virtual model of the sub-network in terms of constructs comprehensible to a public, global routing system of a network, where the virtual model contains a link-state description of an idealized sub-network that represents an actual sub-network, where the idealized sub-network includes: nodes of the sub-network that are also nodes of the network, links among the nodes, where a connected path exists through the idealized sub-network between two nodes of the idealized sub-network if there exists a connected path between the two nodes through the actual sub-network, where a degree of the idealized sub-network is less than a degree of the actual sub-network, and where a set of links in the idealized sub-network changes less frequently than a set of links in the actual sub-network; costs associated with the links, where a cost of a shortest connected path between two nodes of the idealized sub-network approximates a cost of a shortest connected path between the two nodes of the actual sub-network, and where costs associated with the links in the idealized sub-network change less frequently than costs associated with the actual sub-network, employing the virtual model and public, global routing system together with the private, internal routing system of the sub-network for routing within the sub-network, where the virtual model and public, global routing system are used to select among two or more potential exit points from the sub-network for traffic that will exit or transit the sub-network, and where the private, internal routing system is used to select the internal route to the exit point; distributing the virtual model to routers in the network for routing within the network, where the routers use the virtual model to select a preferred entry point to the sub-network from among two or more potential entry points for traffic that will enter or transit the sub-network.