Check if request IP address is in the allowed list

If we want to check if the IP address of mvc request if within a valid ip addresses list, we can do so by using "REMOTE_ADDR" header.

Lets say our ip addresses are saved in a string list

List<string> IPAddresses;

Then we could use a method like this to authenticate inside a custom ActionFilterAttribute

protected virtual bool IsAuthentic(AuthenticationChallengeContext filterContext)

        {

            if (IPAddresses.Length > 0)

            {

                var ip = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];

                if (!string.IsNullOrWhiteSpace(ip) && !((Mode == IPRestrictAttributeModes.Allow) == (IPAddresses.Any(addr => parse(addr).Equals(parse(ip))))))

                {

                    // The user is not in any of the listed ips =>

                    // show the unauthorized view

                    filterContext.Result = new ViewResult

                    {

                        

                        ViewName = "~/Views/Shared/Unauthorized.cshtml"

                    };

                    return false;

                }

            }

           

            return Mode == IPRestrictAttributeModes.Deny;

        }

The parse method parses ip address from string which is

// This method calls the IPAddress.Parse method to check the ipAddress

        // input string. If the ipAddress argument represents a syntatically correct IPv4 or

        // IPv6 address, the method displays the Parse output into quad-notation or

        // colon-hexadecimal notation, respectively. Otherwise, it displays an

        // error message.

        private static IPAddress parse(string ipAddress)

        {

            try

            {

                // Create an instance of IPAddress for the specified address string (in

                // dotted-quad, or colon-hexadecimal notation).

                IPAddress address = IPAddress.Parse(ipAddress);

                // Display the address in standard notation.

                //Console.WriteLine("Parsing your input string: " + "\"" + ipAddress + "\"" + " produces this address (shown in its standard notation): " + address.ToString());

                return address.MapToIPv4();

            }

            catch (ArgumentNullException e)

            {

                throw;

            }

            catch (FormatException e)

            {

                throw;

            }

            catch (Exception e)

            {

                throw;

            }

            return null;

        }