Get client IP address for WCF, post operation

I am trying to determine the client's IP address following this link: http://www.danrigsby.com/blog/index.php/2008/05/21/get-the-clients-address-in-wcf/

In .Net 3.0 there was not a reliable way to obtain the address of the client connecting to a WCF service. In .Net 3.5 a new property was introduced called RemoteEndpointMessageProperty. This property gives you the IP address and port that the client connection came into the service on. Obtaining the this information is pretty straight forward. Just pull it from the IncomingMessageProperties of the current OperationContext by the RemoteEndpointMessageProperty.Name and access the Address and Port properties.

> [ServiceContract] public interface IMyService {
>     [OperationContract]
>     string GetAddressAsString(); }
> 
> public class MyService : IMyService {
>     public string GetAddressAsString()
>     {
>         RemoteEndpointMessageProperty clientEndpoint =
>             OperationContext.Current.IncomingMessageProperties[
>             RemoteEndpointMessageProperty.Name] as RemoteEndpointMessageProperty;
> 
>         return String.Format(
>             "{0}:{1}",
>             clientEndpoint.Address, clientEndpoint.Port);
>     } } 

Things to note:

1. This property only works on http and tcp transports. On all other transports such as MSMQ and NamedPipes, this property will not be available.
2. The address and port are reported by the socket or http.sys of the service’s machine. So if the client came in over a VPN or some other proxy that modified the address, that new address will be represented instead of the client’s local address. This is desirable and important because this is the address and port that the