diff --git a/src/daemon/db-mgr.cpp b/src/daemon/db-mgr.cpp
index b925f2d..5652de2 100644
--- a/src/daemon/db-mgr.cpp
+++ b/src/daemon/db-mgr.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2017, Regents of the University of California.
+ * Copyright (c) 2014-2018, 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.
@@ -125,6 +125,37 @@
   NDNS_LOG_INFO("clear all the data in the database: " << m_dbFile);
 }
 
+
+void
+DbMgr::saveName(const Name& name, sqlite3_stmt* stmt, int iCol, bool isStatic)
+{
+  const Block& wire = name.wireEncode();
+  sqlite3_bind_blob(stmt, iCol, wire.value(), wire.value_size(), isStatic ? SQLITE_STATIC : SQLITE_TRANSIENT);
+}
+
+Name
+DbMgr::restoreName(sqlite3_stmt* stmt, int iCol)
+{
+  Name name;
+
+  const uint8_t* buffer = static_cast<const uint8_t*>(sqlite3_column_blob(stmt, iCol));
+  size_t nBytesLeft = sqlite3_column_bytes(stmt, iCol);
+
+  while (nBytesLeft > 0) {
+    bool hasDecodingSucceeded;
+    name::Component component;
+    std::tie(hasDecodingSucceeded, component) = Block::fromBuffer(buffer, nBytesLeft);
+    if (!hasDecodingSucceeded) {
+      BOOST_THROW_EXCEPTION(Error("Error while decoding name from the database"));
+    }
+    name.append(component);
+    buffer += component.size();
+    nBytesLeft -= component.size();
+  }
+
+  return name;
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 // Zone
 ///////////////////////////////////////////////////////////////////////////////////////////////////
@@ -142,8 +173,8 @@
     BOOST_THROW_EXCEPTION(PrepareError(sql));
   }
 
-  const Block& zoneName = zone.getName().wireEncode();
-  sqlite3_bind_blob(stmt, 1, zoneName.wire(), zoneName.size(), SQLITE_STATIC);
+
+  saveName(zone.getName(), stmt, 1);
   sqlite3_bind_int(stmt,  2, zone.getTtl().count());
 
   rc = sqlite3_step(stmt);
@@ -233,8 +264,7 @@
     BOOST_THROW_EXCEPTION(PrepareError(sql));
   }
 
-  const Block& zoneName = zone.getName().wireEncode();
-  sqlite3_bind_blob(stmt, 1, zoneName.wire(), zoneName.size(), SQLITE_STATIC);
+  saveName(zone.getName(), stmt, 1);
 
   if (sqlite3_step(stmt) == SQLITE_ROW) {
     zone.setId(sqlite3_column_int64(stmt, 0));
@@ -266,8 +296,7 @@
     Zone& zone = vec.back();
     zone.setId(sqlite3_column_int64(stmt, 0));
     zone.setTtl(time::seconds(sqlite3_column_int(stmt, 2)));
-    zone.setName(Name(Block(static_cast<const uint8_t*>(sqlite3_column_blob(stmt, 1)),
-                            sqlite3_column_bytes(stmt, 1))));
+    zone.setName(restoreName(stmt, 1));
   }
   sqlite3_finalize(stmt);
 
@@ -331,8 +360,7 @@
 
   sqlite3_bind_int64(stmt, 1, rrset.getZone()->getId());
 
-  const Block& label = rrset.getLabel().wireEncode();
-  sqlite3_bind_blob(stmt,  2, label.wire(),              label.size(),              SQLITE_STATIC);
+  saveName(rrset.getLabel(), stmt, 2);
   sqlite3_bind_blob(stmt,  3, rrset.getType().wire(),    rrset.getType().size(),    SQLITE_STATIC);
   sqlite3_bind_blob(stmt,  4, rrset.getVersion().wire(), rrset.getVersion().size(), SQLITE_STATIC);
   sqlite3_bind_int64(stmt, 5, rrset.getTtl().count());
@@ -374,8 +402,52 @@
 
   sqlite3_bind_int64(stmt, 1, rrset.getZone()->getId());
 
-  const Block& label = rrset.getLabel().wireEncode();
-  sqlite3_bind_blob(stmt, 2, label.wire(), label.size(), SQLITE_STATIC);
+  saveName(rrset.getLabel(), stmt, 2);
+  sqlite3_bind_blob(stmt, 3, rrset.getType().wire(), rrset.getType().size(), SQLITE_STATIC);
+
+  if (sqlite3_step(stmt) == SQLITE_ROW) {
+    rrset.setId(sqlite3_column_int64(stmt, 0));
+    rrset.setTtl(time::seconds(sqlite3_column_int64(stmt, 1)));
+    rrset.setVersion(Block(static_cast<const uint8_t*>(sqlite3_column_blob(stmt, 2)),
+                           sqlite3_column_bytes(stmt, 2)));
+    rrset.setData(Block(static_cast<const uint8_t*>(sqlite3_column_blob(stmt, 3)),
+                        sqlite3_column_bytes(stmt, 3)));
+  }
+  else {
+    rrset.setId(0);
+  }
+  sqlite3_finalize(stmt);
+
+  return rrset.getId() != 0;
+}
+
+bool
+DbMgr::findLowerBound(Rrset& rrset)
+{
+  if (rrset.getZone() == 0) {
+    BOOST_THROW_EXCEPTION(RrsetError("Rrset has not been assigned to a zone"));
+  }
+
+  if (rrset.getZone()->getId() == 0) {
+    bool isFound = find(*rrset.getZone());
+    if (!isFound) {
+      return false;
+    }
+  }
+
+  sqlite3_stmt* stmt;
+  const char* sql =
+    "SELECT id, ttl, version, data FROM rrsets"
+    "    WHERE zone_id=? and label<? and type=? ORDER BY label DESC";
+  int rc = sqlite3_prepare_v2(m_conn, sql, -1, &stmt, 0);
+
+  if (rc != SQLITE_OK) {
+    BOOST_THROW_EXCEPTION(PrepareError(sql));
+  }
+
+  sqlite3_bind_int64(stmt, 1, rrset.getZone()->getId());
+
+  saveName(rrset.getLabel(), stmt, 2);
   sqlite3_bind_blob(stmt, 3, rrset.getType().wire(), rrset.getType().size(), SQLITE_STATIC);
 
   if (sqlite3_step(stmt) == SQLITE_ROW) {
@@ -406,7 +478,7 @@
   std::vector<Rrset> vec;
   sqlite3_stmt* stmt;
   const char* sql = "SELECT id, ttl, version, data, label, type "
-                    "FROM rrsets where zone_id=? ";
+                    "FROM rrsets where zone_id=? ORDER BY label";
 
   int rc = sqlite3_prepare_v2(m_conn, sql, -1, &stmt, 0);
   if (rc != SQLITE_OK) {
@@ -424,8 +496,7 @@
                            sqlite3_column_bytes(stmt, 2)));
     rrset.setData(Block(static_cast<const uint8_t*>(sqlite3_column_blob(stmt, 3)),
                         sqlite3_column_bytes(stmt, 3)));
-    rrset.setLabel(Name(Block(static_cast<const uint8_t*>(sqlite3_column_blob(stmt, 4)),
-                         sqlite3_column_bytes(stmt, 4))));
+    rrset.setLabel(restoreName(stmt, 4));
     rrset.setType(Block(static_cast<const uint8_t*>(sqlite3_column_blob(stmt, 5)),
                   sqlite3_column_bytes(stmt, 5)));
   }
@@ -434,6 +505,33 @@
   return vec;
 }
 
+void
+DbMgr::removeRrsetsOfZoneByType(Zone& zone, const name::Component& type)
+{
+  if (zone.getId() == 0)
+    find(zone);
+
+  if (zone.getId() == 0)
+    BOOST_THROW_EXCEPTION(RrsetError("Attempting to find all the rrsets with a zone does not in the database"));
+
+  sqlite3_stmt* stmt;
+  const char* sql = "DELETE FROM rrsets WHERE zone_id = ? AND type = ?";
+  int rc = sqlite3_prepare_v2(m_conn, sql, -1, &stmt, 0);
+
+  if (rc != SQLITE_OK) {
+    BOOST_THROW_EXCEPTION(PrepareError(sql));
+  }
+
+  sqlite3_bind_int64(stmt, 1, zone.getId());
+  sqlite3_bind_blob(stmt,  2, type.wire(), type.size(), SQLITE_STATIC);
+
+  rc = sqlite3_step(stmt);
+  if (rc != SQLITE_DONE) {
+    sqlite3_finalize(stmt);
+    BOOST_THROW_EXCEPTION(ExecuteError(sql));
+  }
+  sqlite3_finalize(stmt);
+}
 
 void
 DbMgr::remove(Rrset& rrset)
diff --git a/src/daemon/db-mgr.hpp b/src/daemon/db-mgr.hpp
index 04b9672..ff0066e 100644
--- a/src/daemon/db-mgr.hpp
+++ b/src/daemon/db-mgr.hpp
@@ -166,6 +166,20 @@
   find(Rrset& rrset);
 
   /**
+   * @brief get the data from db according to `m_zone`, `m_label`, `m_type`.
+   *
+   * The lower bound rrset is the largest label that is less than rrset's label
+   * If record exists, `m_ttl`, `m_version` and `m_data` is set
+   *
+   * @pre m_rrset.getZone().getId() > 0
+   * @post whatever the previous id is,
+   *       m_rrset.getId() > 0 if record exists, otherwise m_rrset.getId() == 0
+   * @return true if the record exist
+   */
+  bool
+  findLowerBound(Rrset& rrset);
+
+  /**
    * @brief get all the rrsets which is stored at given zone
    * @throw RrsetError() if zone does not exist in the database
    * @note if zone.getId() == 0, the function setId for the zone automatically
@@ -183,6 +197,13 @@
   remove(Rrset& rrset);
 
   /**
+   * @brief remove all records of a specific type in a zone
+   */
+  void
+  removeRrsetsOfZoneByType(Zone& zone,
+                           const name::Component& type);
+
+  /**
    * @brief replace ttl, version, and Data with new values
    * @pre m_rrset.getId() > 0
    */
@@ -199,6 +220,19 @@
   }
 
 private:
+  /**
+   * @brief Save @p name to the database in the internal sortable format
+   *
+   * If @p name is not preserved until @p stmt is executed, @p isStatic must be
+   * set to `false`.
+   */
+  void
+  saveName(const Name& name, sqlite3_stmt* stmt, int iCol, bool isStatic = true);
+
+  Name
+  restoreName(sqlite3_stmt* stmt, int iCol);
+
+private:
   std::string m_dbFile;
   sqlite3* m_conn;
 };
diff --git a/src/daemon/name-server.cpp b/src/daemon/name-server.cpp
index 11ad3a8..c7649ef 100644
--- a/src/daemon/name-server.cpp
+++ b/src/daemon/name-server.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2017, Regents of the University of California.
+ * Copyright (c) 2014-2018, 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.
@@ -91,14 +91,24 @@
     m_face.put(*answer);
   }
   else {
-    // no record, construct NACK
     Name name = interest.getName();
     name.appendVersion();
     shared_ptr<Data> answer = make_shared<Data>(name);
+    Rrset doe(&m_zone);
+    // currently, there is only one DoE record contains everything
+    doe.setLabel(Name(re.rrLabel).append(re.rrType));
+    doe.setType(label::DOE_RR_TYPE);
+    if (!m_dbMgr.findLowerBound(doe)) {
+        NDNS_LOG_FATAL("fail to find DoE record of zone:" + m_zone.getName().toUri());
+        BOOST_THROW_EXCEPTION(std::runtime_error("fail to find DoE record of zone:" + m_zone.getName().toUri()));
+    }
+
+    answer->setContent(doe.getData());
     answer->setFreshnessPeriod(this->getContentFreshness());
     answer->setContentType(NDNS_NACK);
+    // give this NACk a random signature
+    m_keyChain.sign(*answer);
 
-    m_keyChain.sign(*answer, signingByCertificate(m_certName));
     NDNS_LOG_TRACE("answer query with NDNS-NACK: " << answer->getName());
     m_face.put(*answer);
   }
diff --git a/src/daemon/rrset-factory.cpp b/src/daemon/rrset-factory.cpp
index 4351fcd..3bfca03 100644
--- a/src/daemon/rrset-factory.cpp
+++ b/src/daemon/rrset-factory.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2017, Regents of the University of California.
+ * Copyright (c) 2014-2018, 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.
@@ -77,7 +77,7 @@
 std::pair<Rrset, Name>
 RrsetFactory::generateBaseRrset(const Name& label,
                                 const name::Component& type,
-                                const uint64_t version,
+                                uint64_t version,
                                 const time::seconds& ttl)
 {
   Rrset rrset(&m_zone);
@@ -117,7 +117,7 @@
 
 Rrset
 RrsetFactory::generateNsRrset(const Name& label,
-                              const uint64_t version,
+                              uint64_t version,
                               time::seconds ttl,
                               const ndn::DelegationList& delegations)
 {
@@ -144,7 +144,7 @@
 
 Rrset
 RrsetFactory::generateTxtRrset(const Name& label,
-                               const uint64_t version,
+                               uint64_t version,
                                time::seconds ttl,
                                const std::vector<std::string>& strings)
 {
@@ -178,7 +178,7 @@
 
 Rrset
 RrsetFactory::generateCertRrset(const Name& label,
-                                const uint64_t version,
+                                uint64_t version,
                                 time::seconds ttl,
                                 const ndn::security::v2::Certificate& cert)
 {
@@ -205,7 +205,7 @@
 
 Rrset
 RrsetFactory::generateAuthRrset(const Name& label,
-                                const uint64_t version,
+                                uint64_t version,
                                 time::seconds ttl)
 {
   if (!m_checked) {
@@ -228,6 +228,39 @@
   return rrset;
 }
 
+Rrset
+RrsetFactory::generateDoeRrset(const Name& label,
+                               uint64_t version,
+                               time::seconds ttl,
+                               const Name& lowerLabel,
+                               const Name& upperLabel)
+{
+  if (!m_checked) {
+    BOOST_THROW_EXCEPTION(Error("You have to call checkZoneKey before call generate functions"));
+  }
+
+  if (ttl == DEFAULT_RR_TTL)
+    ttl = m_zone.getTtl();
+
+  Name name;
+  Rrset rrset;
+  std::tie(rrset, name) = generateBaseRrset(label, label::DOE_RR_TYPE, version, ttl);
+
+  std::vector<Block> range;
+  range.push_back(lowerLabel.wireEncode());
+  range.push_back(upperLabel.wireEncode());
+
+  Data data(name);
+  data.setContent(wireEncode(range));
+
+  setContentType(data, NDNS_DOE, ttl);
+  sign(data);
+  rrset.setData(data.wireEncode());
+
+  return rrset;
+}
+
+
 void
 RrsetFactory::sign(Data& data)
 {
diff --git a/src/daemon/rrset-factory.hpp b/src/daemon/rrset-factory.hpp
index 59b3b09..e8babc7 100644
--- a/src/daemon/rrset-factory.hpp
+++ b/src/daemon/rrset-factory.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2017, Regents of the University of California.
+ * Copyright (c) 2014-2018, 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.
@@ -61,27 +61,38 @@
 
   Rrset
   generateNsRrset(const Name& label,
-                  const uint64_t version,
+                  uint64_t version,
                   time::seconds ttl,
                   const ndn::DelegationList& delegations);
 
   Rrset
   generateTxtRrset(const Name& label,
-                   const uint64_t version,
+                   uint64_t version,
                    time::seconds ttl,
                    const std::vector<std::string>& contents);
 
   Rrset
   generateAuthRrset(const Name& label,
-                    const uint64_t version,
+                    uint64_t version,
                     time::seconds ttl);
 
   Rrset
   generateCertRrset(const Name& label,
-                    const uint64_t version,
+                    uint64_t version,
                     time::seconds ttl,
                     const ndn::security::v2::Certificate& cert);
 
+  /**
+   * @brief DoE records are just txt records of all entries of a zone
+   * which means the any range showed in this record does not exist
+   */
+  Rrset
+  generateDoeRrset(const Name& label,
+                   uint64_t version,
+                   time::seconds ttl,
+                   const Name& lowerLabel,
+                   const Name& upperLabel);
+
   static std::vector<std::string>
   wireDecodeTxt(const Block& wire);
 
@@ -94,7 +105,7 @@
   std::pair<Rrset, Name>
   generateBaseRrset(const Name& label,
                     const name::Component& type,
-                    const uint64_t version,
+                    uint64_t version,
                     const time::seconds& ttl);
 
   bool
diff --git a/src/daemon/rrset.cpp b/src/daemon/rrset.cpp
index 96ffce7..75c4d81 100644
--- a/src/daemon/rrset.cpp
+++ b/src/daemon/rrset.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014, Regents of the University of California.
+/*
+ * Copyright (c) 2014-2018, 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.
@@ -57,5 +57,25 @@
 
 }
 
+bool
+Rrset::operator<(const Rrset& other) const
+{
+  if (getZone() != other.getZone() ||
+      (getZone() != nullptr && *getZone() != *other.getZone())) {
+    BOOST_THROW_EXCEPTION(std::runtime_error("Cannot compare Rrset that belong to different zones"));
+  }
+
+  bool isLess = getLabel() < other.getLabel();
+  if (!isLess && getLabel() == other.getLabel()) {
+    isLess = getType() < other.getType();
+
+    if (!isLess && getType() == other.getType()) {
+      isLess = getVersion() < other.getVersion();
+    }
+  }
+  return isLess;
+}
+
+
 } // namespace ndns
 } // namespace ndn
diff --git a/src/daemon/rrset.hpp b/src/daemon/rrset.hpp
index aaedcfe..0e4b883 100644
--- a/src/daemon/rrset.hpp
+++ b/src/daemon/rrset.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014, Regents of the University of California.
+/*
+ * Copyright (c) 2014-2018, 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.
@@ -187,6 +187,9 @@
     return !(*this == other);
   }
 
+  bool
+  operator<(const Rrset& other) const;
+
 private:
   uint64_t m_id;
   Zone* m_zone;