IPAddress.IsLoopback(IPAddress) Method

Definition

Namespace:

System.Net

Assemblies:

netstandard.dll, System.Net.Primitives.dll

Source:

IPAddress.cs

Indicates whether the specified IP address is the loopback address.

C#

public static bool IsLoopback(System.Net.IPAddress address);

Parameters

address

IPAddress

An IP address.

Returns

Boolean

true if address is the loopback address; otherwise, false.

Examples

The following code example uses the IsLoopback method to determine whether the specified address is a loopback address.

C#

using System;
using System.Net;
using System.Net.Sockets;

class IsLoopbackTest
{
  private static void Main(string[] args)
  {
    if (args.Length == 0)
    {
      // No parameters entered. Display program usage.
      Console.WriteLine("Please enter an IP address.");
      Console.WriteLine("Usage:   >ipaddress_isloopback any IPv4 or IPv6 address.");
      Console.WriteLine("Example: >ipaddress_isloopback 127.0.0.1");
      Console.WriteLine("Example: >ipaddress_isloopback 0:0:0:0:0:0:0:1");
      return;
    }
    else
        {
            // Parse the address string entered by the user.
            parse(args[0]);
        }
    }

  // This method calls the IPAddress.Parse method to check if the
  // passed ipAddress parameter is in the correct format.
  // Then it checks whether it represents a loopback address.
  // Finally, it displays the results.
  private static void parse(string ipAddress)
  {
    string loopBack=" is not a loopback address.";

    try
    {
      // Perform syntax check by parsing the address string entered by the user.
      IPAddress address = IPAddress.Parse(ipAddress);

      // Perform semantic check by verifying that the address is a valid IPv4
      // or IPv6 loopback address.
      if(IPAddress.IsLoopback(address)&& address.AddressFamily == AddressFamily.InterNetworkV6)
        loopBack =  " is an IPv6 loopback address " +
                    "whose internal format is: " + address.ToString() + ".";
      else
        if(IPAddress.IsLoopback(address) && address.AddressFamily == AddressFamily.InterNetwork)
          loopBack = " is an IPv4 loopback address " +
                     "whose internal format is: " + address.ToString() + ".";

      // Display the results.
      Console.WriteLine("Your input address: " + "\"" + ipAddress + "\"" + loopBack);
    }

    catch(FormatException e)
    {
      Console.WriteLine("FormatException caught!!!");
      Console.WriteLine("Source : " + e.Source);
      Console.WriteLine("Message : " + e.Message);
    }

    catch(Exception e)
    {
      Console.WriteLine("Exception caught!!!");
      Console.WriteLine("Source : " + e.Source);
      Console.WriteLine("Message : " + e.Message);
    }
   }
}

Remarks

The IsLoopback method compares address to Loopback and returns true if the two IP addresses are the same.

In the case of IPv4, that the IsLoopback method returns true for any IP address of the form 127.X.Y.Z (where X, Y, and Z are in the range 0-255), not just Loopback (127.0.0.1).

Applies to