Probable fix for GitHub issue #63 - do not unite() if either path is TCP, since doing so can result in asymmetric failed NAT-t over UDP if one side has a firewall that permits outgoing UDP but not incoming.

node/Socket.hpp

@@ -80,6 +80,15 @@ public:
 		return _type;
 	}
 
+	/**
+	 * @return True if this is a UDP socket
+	 */
+	inline bool udp() const
+		throw()
+	{
+		return ((_type == ZT_SOCKET_TYPE_UDP_V4)||(_type == ZT_SOCKET_TYPE_UDP_V6));
+	}
+
 	/**
 	 * @return True if this is a TCP socket
 	 */