Sort IP address
Sorting IP addresses using sort is not easy because the dot confuses sort.
This line makes it possible to sort by the whole value of the address
sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 ipaddresses.txt
You can also sort by the last octet
sort -r. -n +3.0 ipaddresses.txt