@Override
  public synchronized void doStart() throws NatInitializationException {
    LOG.info("Starting UPnP Service");
    try {
      upnpService.startup();
      upnpService.getRegistry().addListener(registryListener);
      initiateExternalIpQuery();
    } catch (Exception e) {
      throw new NatInitializationException("Failed start UPnP nat service.", e);
    }
  }
Start the manager. Must not be in started state.

@throws IllegalStateException if already started.
nat/src/main/java/org/hyperledger/besu/nat/upnp/UpnpNatManager.java