diff --git a/network/TcpSocket.h b/network/TcpSocket.h
index 9533340..7469782 100644
--- a/network/TcpSocket.h
+++ b/network/TcpSocket.h
@@ -32,8 +32,14 @@
 
 #include <list>
 
+/* Tunnelling support. */
+#define TUNNEL_PORT_OFFSET 5500
+
 namespace network {
 
+  /* Tunnelling support. */
+  int findFreeTcpPort (void);
+
   class TcpSocket : public Socket {
   public:
     TcpSocket(int sock, bool close=true);