Private IP Address Identifier in Regular Expression

Question

I\'m wondering if this is the best way to match a string that starts with a private IP address (Perl-style Regex):

(^127\\.0\\.0\\.1)|(^192\\.168)|(^10\\.)|(         


        

Answer 1

here is what I use in python:

rfc1918 = re.compile('^(10(\.(25[0-5]|2[0-4][0-9]|1[0-9]{1,2}|[0-9]{1,2})){3}|((172\.(1[6-9]|2[0-9]|3[01]))|192\.168)(\.(25[0-5]|2[0-4][0-9]|1[0-9]{1,2}|[0-9]{1,2})){2})$')

You can remove the ^ and/or $ anchors if you wish.

I prefer the above regex because it weeds out invalid octets (anything above 255).

example usage:

if rfc1918.match(ip):
    print "ip is private"