Question

This simple WCF discovery example works on a single machine but when the client and server are running on separate machines in the same subnet with no firewall, it doesn’t work. What am I missing?

using System;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.ServiceModel;
using System.ServiceModel.Discovery;

namespace WCFDiscovery
{
   class Program
   {
      static void Main(string[] args)
      {
         try { if (args.Length > 0) StartClient(); else StartServer(); }
         catch (Exception ex) { Console.WriteLine(ex); }
         finally { Console.WriteLine("press enter to quit..."); Console.ReadLine(); }
      }

      private static void StartServer()
      {
         var ipAddress = Dns.GetHostAddresses(Dns.GetHostName()).First(ip => ip.AddressFamily == AddressFamily.InterNetwork);
         var address = new Uri(string.Format("net.tcp://{0}:3702", ipAddress));
         var host = new ServiceHost(typeof(Service), address);
         host.AddServiceEndpoint(typeof(IService), new NetTcpBinding(), address);
         host.Description.Behaviors.Add(new ServiceDiscoveryBehavior());
         host.AddServiceEndpoint(new UdpDiscoveryEndpoint());
         host.Open();
         Console.WriteLine("Started on {0}", address);
      }

      private static void StartClient()
      {
         var dc = new DiscoveryClient(new UdpDiscoveryEndpoint());
         Console.WriteLine("Searching for service...");
         var findResponse = dc.Find(new FindCriteria(typeof(IService)));
         var response = ChannelFactory<IService>.CreateChannel(new NetTcpBinding(), findResponse.Endpoints[0].Address).Add(1, 2);
         Console.WriteLine("Service response: {0}", response);
      }
   }

   [ServiceContract] interface IService { [OperationContract] int Add(int x, int y); }

   class Service : IService { public int Add(int x, int y) { return x + y; } }
}

Answer 1

I’ve run your code on 2 different machines (notebook (Win7) and tower PC (Win8), .NET FW 4.5, same WiFi network) and received following exception:

A remote side security requirement was not fulfilled during authentication. Try increasing the ProtectionLevel and/or ImpersonationLevel.

This one is due to the service security being underspecified, the endpoint were found. So, the guys in other answers are right – this is a network problem which can’t be fixed by correcting code.
I’d add that another possible source of the problem may be the network switch not permitting UDP broadcasts.