code: public List
  run() throws IOException, ZoneTransferException {
  	try {
  		openConnection();
  		doxfr();
  	}
  	finally {
  		closeConnection();
  	}
  	if (axfr != null)
  		return axfr;
  	return ixfr;
  }
docs: Does the zone transfer.
  @return A list, which is either an AXFR-style response (List of Records),
  and IXFR-style response (List of Deltas), or null, which indicates that
  an IXFR was performed and the zone is up to date.
  @throws IOException The zone transfer failed to due an IO problem.
  @throws ZoneTransferException The zone transfer failed to due a problem
  with the zone transfer itself.