This class seems to work fine on jdk1.5.0_21
Further to this there seems to be a change which went in in jdk1.6.0
(Picked up from the release note of jdk1.6.0)
Enhancement to NetworkInterface
Provides a number of new methods for accessing state and configuration information relating to a system's network adapters. This includes information such as the broadcast address, subnet mask, MAC addresses, and MTU size. See java.net.NetworkInterface
The new class java.net.InterfaceAddress encapsulates all information about a NetworkInterface's IP addresses, including the broadcast address, and subnet prefix length (subnet mask)