1 is the network for an enterprise such as a large company this configuration however is shown by way of illustration in other implementations the present invention is applied to service provider networks that provide communications between enterprise networks and or individuals or even public networks generally the communications network 1 comprises a series of sub networks subnet 1 subnet 4 these subnets typically include groups of network devices or further sub networks as characteristic of many enterprise networks for example the subnets include different types of networks devices for example subnet 2 and subnet 4 include one or more host computers such as workstations 10 or network client computers subnet 4 also includes host computers such as document server 16 subnet 1 and subnet 3 include one or more host computers 15 sql servers 12 1 12 2 and disk array 14 network communications devices interconnect the network devices of the subnets in the illustrated example switches 20 1 20 2 20 3 and 20 4 provide connectivity between the network devices in subnet 1 subnet 2 subnet 3 and subnet 4 respectively and uplinking to a router 18 the router 18 provides connectivity between the switches 20 1 20 2 20 3 20 4 and external networks such as a wide area network or internet 22 the illustrated network layout is not critical.