We had to do something similar on one of my earlier projects. This was not in Java not Perl. IIRC, the developer basically converted the IPv4 address from the dotted notation(4 octets) to a number (32 bit number - each octet contributing a byte) and just sorted the numbers and converted them back to IPv4 dotted notation.

Maybe you can try the same approach.

Hint: Refer to pack/unpack for the conversion from dotted to number and back.

Regards,
Mahesh