Matches a valid IPv4 address.
Contributed by @itsbrunodev
^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$# Valid IPv4 addresses
123.3.123.89
255.255.255.0
# Invalid IPv4 addresses
999.999.999.999
12.3.456
192.168.1.257