1. A method in a data processing system for identifying a subnet address range for a subnet being used in a network, the network utilizing addresses each comprising an ordered series of a fixed number of bits, comprising: (a) determining the addresses of a plurality of hosts within the network; (b) identifying an address prefix for which at least one determined host address has the form “<identified address prefix>0<any address suffix>”, and for which at least one determined address has the form “<identified address prefix>1<any address suffix>”; (c) determining whether the plurality of determined host addresses include either the address “<identified address prefix>0<address suffix comprised entirely of 1s>” or the address “<identified address prefix>1<address suffix comprised entirely of 0s>”; (d) if the plurality of determined host addresses include either the address “<identified address prefix>0<address suffix comprised entirely of 1s >” or the address “<identified address prefix>1<address suffix comprised entirely of 0s>”, identifying the range of addresses that all begin with the identified address prefix as a subnet address range for a subnet being used in a network; (e) if the plurality of determined host addresses include neither the address “<identified address prefix>0<address suffix comprised entirely of 1s >” nor the address “<identified address prefix>1<address suffix comprised entirely of 1s>”: (1) sending one or more test packets requesting a reply each to a determined host address having the form “<identified address prefix>0<any address suffix>” from an address having the form “<identified address prefix>1<any address suffix>”; (2) sending one or more test packets requesting a reply each to a determined host address having the form “<identified address prefix>1<any address suffix>” from an address having the form “<identified address prefix>0<any address suffix>”; (3) determining the number of test packets sent where a reply to the test packet was sent directly from the test packet's destination address to the test packet's source address; and (4) if the number of test packets sent where a reply to the test packet was sent directly from the test packet's destination address to the test packet's source address exceeds a threshold number, identifying the range of addresses that all begin with the identified address prefix as identifying a subnet address range for a subnet being used in a network.