Getting the IP address of server in ASP.NET?

This should work:

 //this gets the ip address of the server pc

  public string GetIPAddress()
  {
     IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName()); // `Dns.Resolve()` method is deprecated.
     IPAddress ipAddress = ipHostInfo.AddressList[0];

     return ipAddress.ToString();
  }

http://wec-library.blogspot.com/2008/03/gets-ip-address-of-server-pc-using-c.html

OR

 //while this gets the ip address of the visitor making the call
  HttpContext.Current.Request.UserHostAddress;

http://www.geekpedia.com/KB32_How-do-I-get-the-visitors-IP-address.html

Request.ServerVariables["LOCAL_ADDR"];

This gives the IP the request came in on for multi-homed servers

The above is slow as it requires a DNS call (and will obviously not work if one is not available). You can use the code below to get a map of the current pc's local IPV4 addresses with their corresponding subnet mask:

public static Dictionary<IPAddress, IPAddress> GetAllNetworkInterfaceIpv4Addresses()
{
    var map = new Dictionary<IPAddress, IPAddress>();

    foreach (var ni in NetworkInterface.GetAllNetworkInterfaces())
    {
        foreach (var uipi in ni.GetIPProperties().UnicastAddresses)
        {
            if (uipi.Address.AddressFamily != AddressFamily.InterNetwork) continue;

            if (uipi.IPv4Mask == null) continue; //ignore 127.0.0.1
            map[uipi.Address] = uipi.IPv4Mask;
        }
    }
    return map;
}

warning: this is not implemented in Mono yet

  //this gets the ip address of the server pc
  public string GetIPAddress()
  {
     string strHostName = System.Net.Dns.GetHostName();
     //IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName()); <-- Obsolete
     IPHostEntry ipHostInfo = Dns.GetHostEntry(strHostName);
     IPAddress ipAddress = ipHostInfo.AddressList[0];

     return ipAddress.ToString();
  }

This will work for IPv4:

public static string GetServerIP()
{            
    IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());

    foreach (IPAddress address in ipHostInfo.AddressList)
    {
        if (address.AddressFamily == AddressFamily.InterNetwork)
            return address.ToString();
    }

    return string.Empty;
}