RegEx for an IP Address

The [ shouldn't be at the start of your pattern. Also, you probably want to use Matches(...).

Try:

String input = @"var product_pic_fn=;var firmware_ver='20.02.024';var wan_ip='92.75.120.206';if (parent.location.href != window.location.href)";
Regex ip = new Regex(@"\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b");
MatchCollection result = ip.Matches(input);
Console.WriteLine(result[0]); 

Very old post, you should use the accepted solution, but consider using the right RegEx for an IPV4 adress :

((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]?)

If you want to avoid special caracters after or before you can use :

^((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]?)$

Try this:

 Match match = Regex.Match(input, @"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}");
 if (match.Success)
 {
     Console.WriteLine(match.Value);
 }

If you just want check correct IP use IPAddress.TryParse

using System.Net;

bool isIP(string host)
{
    IPAddress ip;
    return IPAddress.TryParse(host, out ip);
}