code: public final boolean isExternal(String host, int port, String transport) {
  		if(logger.isDebugEnabled()) {
  			logger.debug("isExternal - host=" + host + ", port=" + port + ", transport=" + transport);
  		}
  		boolean isExternal = true;
  		MobicentsExtendedListeningPoint listeningPoint = sipNetworkInterfaceManager.findMatchingListeningPoint(host, port, transport);
  		if((hostNames.contains(host) || hostNames.contains(host+":" + port) || listeningPoint != null)) {
  			if(logger.isDebugEnabled()) {
  				logger.debug("hostNames.contains(" + host + ")=" +
  						hostNames.contains(host) +
  						"hostNames.contains(" + host + ":" + port + ")=" +
  								hostNames.contains(host+":" + port) +
  						" | listeningPoint found = " +
  						listeningPoint);
  			}
  			isExternal = false;
  		}
  		if(logger.isDebugEnabled()) {
  			logger.debug("the triplet host/port/transport : " +
  					host + "/" +
  					port + "/" +
  					transport + " is external : " + isExternal);
  		}
  		return isExternal;
  	}
docs: Check whether or not the triplet host, port and transport are corresponding to an interface
  @param host can be hostname or ipaddress
  @param port port number
  @param transport transport used
  @return true if the triplet host, port and transport are corresponding to an interface
  false otherwise