there are several Sunbet UDF's in the UDF forum...


a quick search...

Subnet() - will tell if a given ip# is in a specified subnet.
IsInSubnet() - Checks if a given IP address is in a specified subnet
IsInIPRange() - Checks if IP address is part of a network (deprecated)
IsSubnetMask() - Validates subnet masks
CalcNetworkID() - Calculates the Network ID