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Check Local IP Address [C#]

This example shows how to detect whether a host name or IP address belongs to local computer.

Get local computer name

Get local computer host name using static method Dns.GetHostName.

[C#]
string localComputerName = Dns.GetHostName();

Get local IP address list

Get list of computer IP addresses using static method Dns.GetHostAd­dresses. To get list of local IP addresses pass local computer name as a parameter to the method.

[C#]
IPAddress[] localIPs = Dns.GetHostAddresses(Dns.GetHostName());

Check whether an IP address is local

The following method checks if a given host name or IP address is local. First, it gets all IP addresses of the given host, then it gets all IP addresses of the local computer and finally it compares both lists. If any host IP equals to any of local IPs, the host is a local IP. It also checks whether the host is a loopback address (localhost / 127.0.0.1).

[C#]
public static bool IsLocalIpAddress(string host)
{
  try
  { // get host IP addresses
    IPAddress[] hostIPs = Dns.GetHostAddresses(host);
    // get local IP addresses
    IPAddress[] localIPs = Dns.GetHostAddresses(Dns.GetHostName());

    // test if any host IP equals to any local IP or to localhost
    foreach (IPAddress hostIP in hostIPs)
    {
      // is localhost
      if (IPAddress.IsLoopback(hostIP)) return true;
      // is local address
      foreach (IPAddress localIP in localIPs)
      {
        if (hostIP.Equals(localIP)) return true;
      }
    }
  }
  catch { }
  return false;
}

You can test the method for example like this:

[C#]
IsLocalIpAddress("localhost");        // true (loopback name)
IsLocalIpAddress("127.0.0.1");        // true (loopback IP)
IsLocalIpAddress("MyNotebook");       // true (my computer name)
IsLocalIpAddress("192.168.0.1");      // true (my IP)
IsLocalIpAddress("NonExistingName");  // false (non existing computer name)
IsLocalIpAddress("99.0.0.1");         // false (non existing IP in my net)

See also

By Jan Slama, 08-Apr-2008