Something I just learned, with IP addresses

[Paladin2000]

So here I was, trying to figure out why I was having problems with my ASP RegEx validator control. The objective was to match to an IP address, but to allow it to end in "*" in the final octets (that is, 255.255.255.255 is valid, and so is 255.255.255.* or 255.255.*.* or 255.*.*.*). But the validation was failing for 0.0.0.200, or anything over 199 in the last octet. Here is what I had:

ValidationExpression="((1?\d?\d)|(2[0-4]\d)|(25[0-5]))\.(([*]\.[*]\.[*])|(((1?\d?\d)|(2[0-4]\d)|(25[0-5]))\.(([*]\.[*])|(((1?\d?\d)|(2[0-4]\d)|(25[0-5]))\.([*]|((1?\d?\d)|(2[0-4]\d)|(25[0-5])))))))"

Here is the fix:

ValidationExpression="((25[0-5])|(2[0-4]\d)|(1?\d?\d))\.(([*]\.[*]\.[*])|(((25[0-5])|(2[0-4]\d)|(1?\d?\d))\.(([*]\.[*])|(((25[0-5])|(2[0-4]\d)|(1?\d?\d))\.([*]|((25[0-5])|(2[0-4]\d)|(1?\d?\d)))))))"

By reversing the order (priority) of the octet matches, I solved the problem...

[Andreas Gieriet]

You might consider making it more readable, e.g.:

string b = @"25[0-5]|2[0-4]\d|1?\d?\d"; // longest match first
string n = @"(?:"+b+@")"; // wrap into non captuering group
string w = @"(?:\*|"+b+@")"; // allow * and wrap into non captuering group
string d = @"\."; // separating dot
string ip = n+d+w+d+w+d+w; // the whole ip = b.(*|b).(*|b).(*|b)

Cheers Andi