code: function getFqdnForIpAddress(ipAddress, cb) {
    dns.reverse(ipAddress, function(err, fqdns) {
      if (err) {
        cb(err, fqdns);
      } else if (fqdns[0].toLowerCase() === localhostIdentifier) {
        getFqdn(localhostIdentifier, cb);
      } else {
        cb(err, fqdns[0]);
      }
    });
  }
docs: Do a reverse lookup on the IP address and return the first FQDN.