IP Addresses are just numbers. Numbers are comparable. Some are bigger, some are smaller, some are even equal.
Note
the DefaultIPAddressComparer will gladly compare IPAddress of differing address families.
The DefaultIPAddressComparer extends Comparer<IPAddress>. Its behavior is to first compare two IPAddress objects via the IComparer<AddressFamily> and then ordinally based on the IPAddress big-endian unsigned integer value.
By default the DefaultAddressFamilyComparer is used to compare the address families of the addresses, but that may be overridden by providing your own IComparer<AddressFamily> to the appropriate constructor