diff --git a/src/ndns-enum.hpp b/src/ndns-enum.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014, Regents of the University of California.
+ *
+ * This file is part of NDNS (Named Data Networking Domain Name Service).
+ * See AUTHORS.md for complete list of NDNS authors and contributors.
+ *
+ * NDNS is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * NDNS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * NDNS, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef NDNS_NDNS_ENUM_HPP
+#define NDNS_NDNS_ENUM_HPP
+
+#include <string>
+
+namespace ndn {
+namespace ndns {
+
+/**
+ * @brief NdnsType defined in Response.NdnsMetaInfo.NdnsType
+ */
+enum NdnsType {
+  NDNS_NULL = 0, ///< this is not a real type, just mean that MetaInfo does not contain NdnsType
+  NDNS_RESP = 1, ///< response type means there are requested RR
+  NDNS_NACK = 2, ///< no requested RR
+  NDNS_AUTH = 3, ///< only has RR for detailed (longer) label
+
+  NDNS_UNKNOWN = 255
+};
+
+/*
+ * @brief convert the ResponseType to String
+ */
+std::string
+toString(NdnsType ndnsType);
+
+} // namespace ndns
+} // namespace ndn
+
+#endif // NDNS_NDNS_ENUM_HPP