Validating a url given by the user?

public static bool IsUrl(string url)
	  {
	    string pattern= "^(https?://)"
	    + "?(([0-9a-z_!~*'().&=+$%-]+: )?[0-9a-z_!~*'().&=+$%-]+@)?" //user@
	    + @"(([0-9]{1,3}\.){3}[0-9]{1,3}" // IP- 199.194.52.184
	    + "|" // allows either IP or domain
	    + @"([0-9a-z_!~*'()-]+\.)*" // tertiary domain(s)- www.
	    + @"([0-9a-z][0-9a-z-]{0,61})?[0-9a-z]\." // second level domain
	    + "[a-z]{2,6})" // first level domain- .com or .museum
	    + "(:[0-9]{1,4})?" // port number- :80
	    + "((/?)|" // a slash isn't required if there is no file name
	    + "(/[0-9a-z_!~*'().;?:@&=+$,%#-]+)+/?)$";
	    Regex rx = new Regex(pattern);
	 
	    if (rx.IsMatch(url))
	      return (true); // if URL is validate
	    else
	      return (false); // if URL is not validate.
	  }