Text box only allow IP address in windows application

private void txtSta2_IP_Adrs_KeyUp(object sender, KeyEventArgs e)

{

if (e.KeyCode == Keys.F1)

{

// Display a pop-up help topic to assist the user.

Help.ShowPopup(txtSta2_IP_Adrs, "enter ip", new Point(txtSta2_IP_Adrs.Right, this.txtSta2_IP_Adrs.Bottom));

}

bool isIPAddress = false;

string pattern = @"\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b";

Regex regex = new Regex(pattern);

isIPAddress = regex.IsMatch(pattern);

//string ip1 = "192.168.0.1";

// string ip2 = "302.0.0.1";

//Regex.IsMatch(ip1, pattern); // returns true

// Regex.IsMatch(ip2, pattern); // returns false

return isIPAddress ;

}