[#4058] Improved ChangeLog

The wiki page is obsolete and apparently not worth updating.
No replacement is available.
Just delete the entire sentence.

.gitlab/issue_templates/release_checklist.md

@@ -5,8 +5,6 @@ about: Create a new issue using this checklist for each release.
 
 # Kea Release Checklist
 
-This is thoroughly documented in [the Kea Release Process guide](https://wiki.isc.org/bin/view/QA/KeaReleaseProcess).
-
 #### Legend
 
 - `A.B.C`: the version being released
@@ -212,7 +210,7 @@ Now it's time to publish the code.
 
 ## Support
 
-1. [ ] Update tickets if any support customers are waiting for the release.
+1. [ ] Update tickets if any support customers are waiting for the release. [:link:](https://wiki.isc.org/bin/view/Main/KeaReleaseSupportUpdateTix)
 
 ## QA
 

changelog_unreleased/226-adaptive-lease-time-threshold

@@ -0,0 +1,7 @@
+[func]		fdupont
+	Added the new "adaptive-lease-time-threshold" parameter
+	for the FLQ (Free Lease Queue) allocator which reduces
+	the lifetime of leases when pools of a subnet have an
+	occupancy rate above a configured threshold (new feature
+	from ISC DHCP).
+	(Gitlab #226)

changelog_unreleased/4058-reused-v6-expired-leases-do-not-get-hardware-address

@@ -0,0 +1,4 @@
+[bug]		fdupont
+	When reusing an expired lease, kea-dhcp6 now correctly saves
+	the client hardware address in the lease.
+	(Gitlab #4058)

doc/examples/kea4/all-keys.json

@@ -989,6 +989,9 @@
                 // lease is returned as it was "cached".
                 "cache-max-age": 1000,
 
+                // Adaptive lease time threshold (1.0 is disabled).
+                "adaptive-lease-time-threshold": 0.8,
+
                 // Specify whether the server should look up global reservations.
                 "reservations-global": false,
 
@@ -1277,6 +1280,9 @@
                         // Subnet-level cache maximum.
                         "cache-max-age": 1000,
 
+                        // Adaptive lease time threshold (1.0 is disabled).
+                        "adaptive-lease-time-threshold": 0.8,
+
                         // List of static IPv4 reservations assigned to clients belonging
                         // to this subnet. For a detailed example, see reservations.json.
                         "reservations": [
@@ -1419,6 +1425,9 @@
         // Global cache maximum.
         "cache-max-age": 1000,
 
+        // Adaptive lease time threshold (1.0 is disabled).
+        "adaptive-lease-time-threshold": 0.8,
+
         // String of zero or more characters with which to replace each
         // invalid character in the hostname or Client FQDN. The default
         // value is an empty string, which will cause invalid characters

doc/examples/kea6/all-keys.json

@@ -939,6 +939,9 @@
                 // lease is returned as it was "cached".
                 "cache-max-age": 1000,
 
+                // Adaptive lease time threshold (1.0 is disabled).
+                "adaptive-lease-time-threshold": 0.8,
+
                 // Specify whether the server should look up global reservations.
                 "reservations-global": false,
 
@@ -1270,6 +1273,9 @@
                         // Subnet-level cache maximum.
                         "cache-max-age": 1000,
 
+                        // Adaptive lease time threshold (1.0 is disabled).
+                        "adaptive-lease-time-threshold": 0.8,
+
                         // List of static IPv6 reservations assigned to clients belonging
                         // to this subnet. For a detailed example, see reservations.json.
                         "reservations": [
@@ -1408,6 +1414,9 @@
         // Global cache maximum.
         "cache-max-age": 1000,
 
+        // Adaptive lease time threshold (1.0 is disabled)
+        "adaptive-lease-time-threshold": 0.8,
+
         // String of zero or more characters with which to replace each
         // invalid character in the Client FQDN. The default
         // value is an empty string, which will cause invalid characters

doc/sphinx/arm/dhcp4-srv.rst

@@ -8985,3 +8985,20 @@ avoiding unnecessary impact on the server's startup time.
    As a result, the servers will not be able to offer some of the available
    leases to the clients. Only a server reclaiming a particular lease will
    be able to offer it.
+
+In Kea 3.1.1 a new parameter ``adaptive-lease-time-threshold`` was added.
+It can be specified at global, shared network and subnet levels and
+takes a floating point value between ``0.0`` (excluded) and ``1.0``.
+It is disabled by default or when set to ``1.0``. It is only supported
+by the FLQ allocator. When the occupancy rate of pools in a subnet is
+above the specified value the server decreases the lease valid lifetime
+to the applicable ``min-valid-lifetime`` for new clients. Clients
+renewing an already existing lease get at least the remaining lifetime
+from the current lease. Since the leases expire faster, the server may
+either recover more quickly or avoid pool exhaustion entirely.
+
+The occupancy rate is defined as being the number of already assigned
+addresses (including the address being assigned) divided by the total
+number of addresses in pools where the address can be allocated from
+(i.e. if the query is not member of a ``client-classes`` guard of a pool
+this pool is not taken into account).

doc/sphinx/arm/dhcp6-srv.rst

@@ -8730,3 +8730,21 @@ avoiding unnecessary impact on the server's startup time.
    As a result, the servers will not be able to offer some of the available
    leases to the clients. Only a server reclaiming a particular lease will
    be able to offer it.
+
+In Kea 3.1.1 a new parameter ``adaptive-lease-time-threshold`` was added.
+It can be specified at global, shared network and subnet levels and
+takes a floating point value between ``0.0`` (excluded) and ``1.0``.
+It is disabled by default or when set to ``1.0``. It is  only supported
+by the FLQ allocator. When the occupancy rate of pools in a subnet is
+above the specified value the server decreases the lease valid lifetime
+to the applicable ``min-valid-lifetime`` for new clients. Clients
+renewing an already existing lease get at least the remaining lifetime
+from the current lease. Since the leases expire faster, the server may
+either recover more quickly or avoid pool exhaustion entirely.
+
+The occupancy rate is defined as being the number of already assigned
+delegated prefixes (including the address being assigned) divided by the total
+number of prefixes in pools where the address can be allocated from
+(i.e. if the query is not member of a ``client-classes`` guard of a pool,
+or if the delegated prefix length is not compatible this pool is not taken
+into account).

src/bin/dhcp4/dhcp4_lexer.ll

@@ -1316,6 +1316,17 @@ ControlCharacterFill            [^"\\]|\\["\\/bfnrtu]
     }
 }
 
+\"adaptive-lease-time-threshold\" {
+    switch(driver.ctx_) {
+    case isc::dhcp::Parser4Context::DHCP4:
+    case isc::dhcp::Parser4Context::SUBNET4:
+    case isc::dhcp::Parser4Context::SHARED_NETWORK:
+        return isc::dhcp::Dhcp4Parser::make_ADAPTIVE_LEASE_TIME_THRESHOLD(driver.loc_);
+    default:
+        return isc::dhcp::Dhcp4Parser::make_STRING("adaptive-lease-time-threshold", driver.loc_);
+    }
+}
+
 \"loggers\" {
     switch(driver.ctx_) {
     case isc::dhcp::Parser4Context::DHCP4:

src/bin/dhcp4/dhcp4_parser.yy

@@ -130,6 +130,7 @@ using namespace std;
   T2_PERCENT "t2-percent"
   CACHE_THRESHOLD "cache-threshold"
   CACHE_MAX_AGE "cache-max-age"
+  ADAPTIVE_LEASE_TIME_THRESHOLD "adaptive-lease-time-threshold"
   DECLINE_PROBATION_PERIOD "decline-probation-period"
   SERVER_TAG "server-tag"
   STATISTIC_DEFAULT_SAMPLE_COUNT "statistic-default-sample-count"
@@ -563,6 +564,7 @@ global_param: valid_lifetime
             | t2_percent
             | cache_threshold
             | cache_max_age
+            | adaptive_lease_time_threshold
             | loggers
             | hostname_char_set
             | hostname_char_replacement
@@ -654,6 +656,12 @@ cache_max_age: CACHE_MAX_AGE COLON INTEGER {
     ctx.stack_.back()->set("cache-max-age", cm);
 };
 
+adaptive_lease_time_threshold: ADAPTIVE_LEASE_TIME_THRESHOLD COLON FLOAT {
+    ctx.unique("adaptive-lease-time-threshold", ctx.loc2pos(@1));
+    ElementPtr altt(new DoubleElement($3, ctx.loc2pos(@3)));
+    ctx.stack_.back()->set("adaptive-lease-time-threshold", altt);
+};
+
 decline_probation_period: DECLINE_PROBATION_PERIOD COLON INTEGER {
     ctx.unique("decline-probation-period", ctx.loc2pos(@1));
     ElementPtr dpp(new IntElement($3, ctx.loc2pos(@3)));
@@ -1683,6 +1691,7 @@ subnet4_param: valid_lifetime
              | t2_percent
              | cache_threshold
              | cache_max_age
+             | adaptive_lease_time_threshold
              | ddns_send_updates
              | ddns_override_no_update
              | ddns_override_client_update
@@ -1887,6 +1896,7 @@ shared_network_param: name
                     | t2_percent
                     | cache_threshold
                     | cache_max_age
+                    | adaptive_lease_time_threshold
                     | ddns_send_updates
                     | ddns_override_no_update
                     | ddns_override_client_update

src/bin/dhcp4/json_config_parser.cc

@@ -662,6 +662,7 @@ processDhcp4Config(isc::data::ConstElementPtr config_set) {
                  (config_pair.first == "t2-percent") ||
                  (config_pair.first == "cache-threshold") ||
                  (config_pair.first == "cache-max-age") ||
+                 (config_pair.first == "adaptive-lease-time-threshold") ||
                  (config_pair.first == "hostname-char-set") ||
                  (config_pair.first == "hostname-char-replacement") ||
                  (config_pair.first == "ddns-send-updates") ||

src/bin/dhcp4/tests/flq_unittest.cc

@@ -0,0 +1,313 @@
+// Copyright (C) 2025 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <asiolink/io_address.h>
+#include <dhcp/dhcp4.h>
+#include <dhcp/option_int.h>
+#include <dhcp/testutils/iface_mgr_test_config.h>
+#include <dhcp4/tests/dhcp4_test_utils.h>
+#include <dhcp4/tests/dhcp4_client.h>
+#include <gtest/gtest.h>
+
+using namespace isc;
+using namespace isc::asiolink;
+using namespace isc::dhcp;
+using namespace isc::dhcp::test;
+
+namespace {
+
+/// @brief JSON configuration
+std::string FLQ_CONFIG =
+    "{ \"interfaces-config\": {"
+    "      \"interfaces\": [ \"*\" ]"
+    "},"
+    "\"min-valid-lifetime\": 100,"
+    "\"valid-lifetime\": 200,"
+    "\"max-valid-lifetime\": 300,"
+    "\"adaptive-lease-time-threshold\": .5,"
+    "\"cache-threshold\": 0.,"
+    "\"subnet4\": [ { "
+    "    \"subnet\": \"10.0.0.0/24\", "
+    "    \"id\": 1,"
+    "    \"pools\": [ { \"pool\": \"10.0.0.11-10.0.0.14\" } ],"
+    "    \"allocator\": \"flq\""
+    " } ]"
+    "}";
+
+/// @brief Test fixture class for testing FLQ / adaptive-lease-time-threshold.
+class FLQTest : public Dhcpv4SrvTest {
+public:
+    /// @brief Constructor.
+    ///
+    /// Sets up fake interfaces.
+    FLQTest() : Dhcpv4SrvTest(), iface_mgr_test_config_(true) {
+    }
+
+    /// @brief Creates a DHCPv4 lease for an address and MAC address.
+    ///
+    /// @param address Lease address.
+    /// @param hw_address_seed a seed from which the hardware address is generated.
+    /// @return Created lease pointer.
+    Lease4Ptr
+    createLease4(const IOAddress& address, uint64_t hw_address_seed) const {
+        vector<uint8_t> hw_address_vec(sizeof(hw_address_seed));
+        for (unsigned i = 0; i < sizeof(hw_address_seed); ++i) {
+            hw_address_vec[i] = (hw_address_seed >> i) & 0xFF;
+        }
+        HWAddrPtr hw_address(new HWAddr(hw_address_vec, HTYPE_ETHER));
+        Lease4Ptr lease(new Lease4(address, hw_address, ClientIdPtr(),
+                                   600, time(0), 1));
+        return (lease);
+    }
+
+    /// @brief Check the response.
+    ///
+    /// @param resp the response.
+    /// @param expected the expected lifetime.
+    /// @param near use near comparision (when true) or equality (when false).
+    void checkResponse(Pkt4Ptr resp, uint32_t expected, bool near = false) {
+        ASSERT_TRUE(resp);
+
+        // Make sure that the server has responded with DHCPACK.
+        ASSERT_EQ(DHCPACK, static_cast<int>(resp->getType()));
+
+        // Make sure that the client has got the requested address.
+        EXPECT_EQ("10.0.0.14", resp->getYiaddr().toText());
+
+        // Verify the valid liftime.
+        OptionUint32Ptr opt = boost::dynamic_pointer_cast<
+            OptionUint32>(resp->getOption(DHO_DHCP_LEASE_TIME));
+        ASSERT_TRUE(opt);
+        if (near) {
+            EXPECT_NEAR(expected, opt->getValue(), 2);
+        } else {
+            EXPECT_EQ(expected, opt->getValue());
+        }
+    }
+
+    /// @brief Allocate all pool leases leaving the last one free.
+    void fill() {
+        auto& lease_mgr = LeaseMgrFactory::instance();
+        auto lease1 = createLease4(IOAddress("10.0.0.11"), 1);
+        EXPECT_TRUE(lease_mgr.addLease(lease1));
+        auto lease2 = createLease4(IOAddress("10.0.0.12"), 2);
+        EXPECT_TRUE(lease_mgr.addLease(lease2));
+        auto lease3 = createLease4(IOAddress("10.0.0.13"), 3);
+        EXPECT_TRUE(lease_mgr.addLease(lease3));
+    }
+
+    /// @brief Age and commit a lease.
+    ///
+    /// @param lease the lease.
+    /// @param delay the amount of time backward.
+    /// @param update when false add the lease, when true update the lease.
+    /// @param reclaim when true change the state.
+    void ageLease(Lease4Ptr lease, uint32_t delay, bool update,
+                  bool reclaim = false) {
+        ASSERT_TRUE(lease);
+        lease->cltt_ -= delay;
+        lease->current_cltt_ -= delay;
+        if (reclaim) {
+            lease->state_ = Lease::STATE_EXPIRED_RECLAIMED;
+        }
+        auto& lease_mgr = LeaseMgrFactory::instance();
+        if (update) {
+            EXPECT_NO_THROW(lease_mgr.updateLease4(lease));
+        } else {
+            EXPECT_TRUE(lease_mgr.addLease(lease));
+        }
+    }
+
+    /// @brief Interface Manager's fake configuration control.
+    IfaceMgrTestConfig iface_mgr_test_config_;
+};
+
+// Test allocation with empty pool.
+TEST_F(FLQTest, empty) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Perform 4-way exchange with the server requesting the last address.
+    boost::shared_ptr<IOAddress> hint(new IOAddress("10.0.0.14"));
+    ASSERT_NO_THROW(client.doDORA(hint));
+
+    // Valid lifetime should be the valid-lifetime parameter value (200).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 200);
+}
+
+// Test allocation with almost full pool.
+TEST_F(FLQTest, last) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Create leases for the first addresses.
+    fill();
+
+    // Perform 4-way exchange with the server.
+    ASSERT_NO_THROW(client.doDORA());
+
+    // Valid lifetime should be the min-valid-lifetime parameter value (100).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 100);
+}
+
+// Test allocation with an expired lease.
+TEST_F(FLQTest, expired) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Create leases for the first addresses.
+    fill();
+
+    // Create and expire last lease.
+    auto lease = createLease4(IOAddress("10.0.0.14"), 4);
+    ageLease(lease, 1000, false);
+    ASSERT_TRUE(lease->expired());
+
+    // Perform 4-way exchange with the server.
+    ASSERT_NO_THROW(client.doDORA());
+
+    // Valid lifetime should be the min-valid-lifetime parameter value (100).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 100);
+}
+
+// Test allocation with a reclaimed lease.
+TEST_F(FLQTest, reclaimed) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Create leases for the first addresses.
+    fill();
+
+    // Create and reclaim last lease.
+    auto lease = createLease4(IOAddress("10.0.0.14"), 4);
+    ageLease(lease, 1000, false, true);
+
+    // Perform 4-way exchange with the server.
+    ASSERT_NO_THROW(client.doDORA());
+
+    // Valid lifetime should be the min-valid-lifetime parameter value (100).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 100);
+}
+
+// Test renewal with almost empty pool.
+TEST_F(FLQTest, renew) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Obtain a lease from the server using the 4-way exchange.
+    boost::shared_ptr<IOAddress> hint(new IOAddress("10.0.0.14"));
+    ASSERT_NO_THROW(client.doDORA(hint));
+
+    // Valid lifetime should be the valid-lifetime parameter value (200).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 200);
+
+    // Age the lease.
+    auto& lease_mgr = LeaseMgrFactory::instance();
+    Lease4Ptr lease = lease_mgr.getLease4(*hint);
+    ageLease(lease, 150, true);
+    ASSERT_FALSE(lease->expired());
+
+    // Let's transition the client to Renewing state.
+    client.setState(Dhcp4Client::RENEWING);
+
+    // Set the unicast destination address to indicate that it is a renewal.
+    client.setDestAddress(IOAddress("10.0.0.1"));
+    ASSERT_NO_THROW(client.doRequest());
+
+    // Valid lifetime should be the valid-lifetime parameter value (200).
+    resp = client.getContext().response_;
+    checkResponse(resp, 200);
+}
+
+// Test renewal with full pool.
+TEST_F(FLQTest, renewFull) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Obtain a lease from the server using the 4-way exchange.
+    boost::shared_ptr<IOAddress> hint(new IOAddress("10.0.0.14"));
+    ASSERT_NO_THROW(client.doDORA(hint));
+
+    // Valid lifetime should be the valid-lifetime parameter value (200).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 200);
+
+    // Create leases for the first addresses.
+    fill();
+
+    // Age the lease.
+    auto& lease_mgr = LeaseMgrFactory::instance();
+    Lease4Ptr lease = lease_mgr.getLease4(*hint);
+    ageLease(lease, 150, true);
+    ASSERT_FALSE(lease->expired());
+
+    // Let's transition the client to Renewing state.
+    client.setState(Dhcp4Client::RENEWING);
+
+    // Set the unicast destination address to indicate that it is a renewal.
+    client.setDestAddress(IOAddress("10.0.0.1"));
+    ASSERT_NO_THROW(client.doRequest());
+
+    // Valid lifetime should be the min-valid-lifetime parameter value (100).
+    resp = client.getContext().response_;
+    checkResponse(resp, 100);
+}
+
+// Test renewal with full pool but remaining lifetime greater than minimal.
+TEST_F(FLQTest, renewRemaining) {
+    Dhcp4Client client(srv_, Dhcp4Client::SELECTING);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Obtain a lease from the server using the 4-way exchange.
+    boost::shared_ptr<IOAddress> hint(new IOAddress("10.0.0.14"));
+    ASSERT_NO_THROW(client.doDORA(hint));
+
+    // Valid lifetime should be the valid-lifetime parameter value (200).
+    Pkt4Ptr resp = client.getContext().response_;
+    checkResponse(resp, 200);
+
+    // Create leases for the first addresses.
+    fill();
+
+    // Age the lease but only by 50 seconds.
+    auto& lease_mgr = LeaseMgrFactory::instance();
+    Lease4Ptr lease = lease_mgr.getLease4(*hint);
+    ageLease(lease, 50, true);
+    ASSERT_FALSE(lease->expired());
+
+    // Let's transition the client to Renewing state.
+    client.setState(Dhcp4Client::RENEWING);
+
+    // Set the unicast destination address to indicate that it is a renewal.
+    client.setDestAddress(IOAddress("10.0.0.1"));
+    ASSERT_NO_THROW(client.doRequest());
+
+    // Valid lifetime should be the remaining lifetime so ~150 seconds.
+    resp = client.getContext().response_;
+    checkResponse(resp, 150, true);
+}
+
+}

src/bin/dhcp4/tests/meson.build

@@ -126,6 +126,7 @@ kea_dhcp4_tests = executable(
     'dhcp4to6_ipc_unittest.cc',
     'direct_client_unittest.cc',
     'dora_unittest.cc',
+    'flq_unittest.cc',
     'fqdn_unittest.cc',
     'get_config_unittest.cc',
     'hooks_unittest.cc',

src/bin/dhcp4/tests/simple_parser4_unittest.cc

@@ -210,6 +210,6 @@ TEST_F(SimpleParser4Test, optionDefDefaults4) {
     checkBoolValue(def, "array", false);
 }
 
-};
-};
-};
+}
+}
+}

src/bin/dhcp6/dhcp6_lexer.ll

@@ -1169,7 +1169,7 @@ ControlCharacterFill            [^"\\]|\\["\\/bfnrtu]
         return isc::dhcp::Dhcp6Parser::make_STRING("ddns-ttl-percent", driver.loc_);
     }
 }
- 
+
 \"ddns-ttl\" {
     switch(driver.ctx_) {
     case isc::dhcp::Parser6Context::DHCP6:
@@ -1613,6 +1613,17 @@ ControlCharacterFill            [^"\\]|\\["\\/bfnrtu]
     }
 }
 
+\"adaptive-lease-time-threshold\" {
+    switch(driver.ctx_) {
+    case isc::dhcp::Parser6Context::DHCP6:
+    case isc::dhcp::Parser6Context::SUBNET6:
+    case isc::dhcp::Parser6Context::SHARED_NETWORK:
+        return isc::dhcp::Dhcp6Parser::make_ADAPTIVE_LEASE_TIME_THRESHOLD(driver.loc_);
+    default:
+        return isc::dhcp::Dhcp6Parser::make_STRING("adaptive-lease-time-threshold", driver.loc_);
+    }
+}
+
 \"loggers\" {
     switch(driver.ctx_) {
     case isc::dhcp::Parser6Context::DHCP6:

src/bin/dhcp6/dhcp6_parser.yy

@@ -115,6 +115,7 @@ using namespace std;
   T2_PERCENT "t2-percent"
   CACHE_THRESHOLD "cache-threshold"
   CACHE_MAX_AGE "cache-max-age"
+  ADAPTIVE_LEASE_TIME_THRESHOLD "adaptive-lease-time-threshold"
   DECLINE_PROBATION_PERIOD "decline-probation-period"
   SERVER_TAG "server-tag"
   STATISTIC_DEFAULT_SAMPLE_COUNT "statistic-default-sample-count"
@@ -568,6 +569,7 @@ global_param: data_directory
             | t2_percent
             | cache_threshold
             | cache_max_age
+            | adaptive_lease_time_threshold
             | loggers
             | hostname_char_set
             | hostname_char_replacement
@@ -686,6 +688,12 @@ cache_max_age: CACHE_MAX_AGE COLON INTEGER {
     ctx.stack_.back()->set("cache-max-age", cm);
 };
 
+adaptive_lease_time_threshold: ADAPTIVE_LEASE_TIME_THRESHOLD COLON FLOAT {
+    ctx.unique("adaptive-lease-time-threshold", ctx.loc2pos(@1));
+    ElementPtr altt(new DoubleElement($3, ctx.loc2pos(@3)));
+    ctx.stack_.back()->set("adaptive-lease-time-threshold", altt);
+};
+
 decline_probation_period: DECLINE_PROBATION_PERIOD COLON INTEGER {
     ctx.unique("decline-probation-period", ctx.loc2pos(@1));
     ElementPtr dpp(new IntElement($3, ctx.loc2pos(@3)));
@@ -1692,6 +1700,7 @@ subnet6_param: preferred_lifetime
              | t2_percent
              | cache_threshold
              | cache_max_age
+             | adaptive_lease_time_threshold
              | hostname_char_set
              | hostname_char_replacement
              | ddns_send_updates
@@ -1884,6 +1893,7 @@ shared_network_param: name
                     | t2_percent
                     | cache_threshold
                     | cache_max_age
+                    | adaptive_lease_time_threshold
                     | hostname_char_set
                     | hostname_char_replacement
                     | ddns_send_updates

src/bin/dhcp6/json_config_parser.cc

@@ -780,6 +780,7 @@ processDhcp6Config(isc::data::ConstElementPtr config_set) {
                  (config_pair.first == "t2-percent") ||
                  (config_pair.first == "cache-threshold") ||
                  (config_pair.first == "cache-max-age") ||
+                 (config_pair.first == "adaptive-lease-time-threshold") ||
                  (config_pair.first == "hostname-char-set") ||
                  (config_pair.first == "hostname-char-replacement") ||
                  (config_pair.first == "ddns-send-updates") ||

src/bin/dhcp6/tests/flq_unittest.cc

@@ -0,0 +1,409 @@
+// Copyright (C) 2025 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <asiolink/io_address.h>
+#include <dhcp/testutils/iface_mgr_test_config.h>
+#include <dhcp6/tests/dhcp6_test_utils.h>
+#include <dhcp6/tests/dhcp6_client.h>
+#include <gtest/gtest.h>
+
+using namespace isc;
+using namespace isc::asiolink;
+using namespace isc::dhcp;
+using namespace isc::dhcp::test;
+
+namespace {
+
+/// @brief JSON configuration
+std::string FLQ_CONFIG =
+    "{ \"interfaces-config\": {"
+    "      \"interfaces\": [ \"*\" ]"
+    "},"
+    "\"min-preferred-lifetime\": 100,"
+    "\"preferred-lifetime\": 200,"
+    "\"max-preferred-lifetime\": 300,"
+    "\"min-valid-lifetime\": 400,"
+    "\"valid-lifetime\": 600,"
+    "\"max-valid-lifetime\": 700,"
+    "\"rebind-timer\": 250,"
+    "\"renew-timer\": 250,"
+    "\"adaptive-lease-time-threshold\": .5,"
+    "\"cache-threshold\": 0.,"
+    "\"subnet6\": [ { "
+    "    \"subnet\": \"3000::/32\", "
+    "    \"id\": 1,"
+    "    \"interface\": \"eth0\","
+    "    \"pd-pools\": [ {"
+    "        \"prefix\": \"2001:db8:1::\","
+    "        \"prefix-len\": 48,"
+    "        \"delegated-len\": 51"
+    "    } ],"
+    "    \"pd-allocator\": \"flq\""
+    " } ]"
+    "}";
+
+/// @brief Test fixture class for testing FLQ / adaptive-lease-time-threshold.
+class FLQTest : public Dhcpv6SrvTest {
+public:
+    /// @brief Constructor.
+    ///
+    /// Sets up fake interfaces.
+    FLQTest() : Dhcpv6SrvTest(), iface_mgr_test_config_(true) {
+    }
+
+    /// @brief Creates a DHCPv6 lease for an address and MAC address.
+    ///
+    /// @param address Lease address.
+    /// @param duid_seed a seed from which the DUID is generated.
+    /// @return Created lease pointer.
+    Lease6Ptr
+    createLease6(const IOAddress& address, uint64_t duid_seed) const {
+        vector<uint8_t> duid_vec(sizeof(duid_seed));
+        for (unsigned i = 0; i < sizeof(duid_seed); ++i) {
+            duid_vec[i] = (duid_seed >> i) & 0xFF;
+        }
+        DuidPtr duid(new DUID(duid_vec));
+        Lease6Ptr lease(new Lease6(Lease::TYPE_PD, address, duid, 1,
+                                   800, 1200, 1, HWAddrPtr(), 51));
+        return (lease);
+    }
+
+    /// @brief Check the returned lease.
+    ///
+    /// @param lease the lease.
+    /// @param exp_preferred the expected preferred lifetime.
+    /// @param exp_valid the expected valid lifetime
+    /// @param near_preferred use near comparision (when true) or equality
+    ///        when false) for the preferred lifetime.
+    /// @param near_valid use near comparision (when true) or equality
+    ///        when false) for the valid lifetime.
+    void checkResponse(Lease6Ptr lease, uint32_t exp_preferred,
+                       uint32_t exp_valid, bool near_preferred = false,
+                       bool near_valid = false) {
+        ASSERT_TRUE(lease);
+
+        // Make sure that the client has got the requested prefix.
+        EXPECT_EQ("2001:db8:1:e000::", lease->addr_.toText());
+        EXPECT_EQ(51, lease->prefixlen_);
+
+        if (near_preferred) {
+            EXPECT_NEAR(exp_preferred, lease->preferred_lft_, 2);
+        } else {
+            EXPECT_EQ(exp_preferred, lease->preferred_lft_);
+        }
+
+        if (near_valid) {
+            EXPECT_NEAR(exp_valid, lease->valid_lft_, 2);
+        } else {
+            EXPECT_EQ(exp_valid, lease->valid_lft_);
+        }
+    }
+
+    /// @brief Allocate all pool leases leaving the last one free.
+    void fill() {
+        auto& lease_mgr = LeaseMgrFactory::instance();
+        auto lease0 = createLease6(IOAddress("2001:db8:1::"), 1);
+        EXPECT_TRUE(lease_mgr.addLease(lease0));
+        auto lease1 = createLease6(IOAddress("2001:db8:1:2000::"), 2);
+        EXPECT_TRUE(lease_mgr.addLease(lease1));
+        auto lease2 = createLease6(IOAddress("2001:db8:1:4000::"), 3);
+        EXPECT_TRUE(lease_mgr.addLease(lease2));
+        auto lease3 = createLease6(IOAddress("2001:db8:1:6000::"), 4);
+        EXPECT_TRUE(lease_mgr.addLease(lease3));
+        auto lease4 = createLease6(IOAddress("2001:db8:1:8000::"), 5);
+        EXPECT_TRUE(lease_mgr.addLease(lease4));
+        auto lease5 = createLease6(IOAddress("2001:db8:1:a000::"), 6);
+        EXPECT_TRUE(lease_mgr.addLease(lease5));
+        auto lease6 = createLease6(IOAddress("2001:db8:1:c000::"), 7);
+        EXPECT_TRUE(lease_mgr.addLease(lease6));
+    }
+
+    /// @brief Age and commit a lease.
+    ///
+    /// @param lease the lease.
+    /// @param delay the amount of time backward.
+    /// @param update when false add the lease, when true update the lease.
+    /// @param reclaim when true change the state.
+    void ageLease(Lease6Ptr lease, uint32_t delay, bool update,
+                  bool reclaim = false) {
+        ASSERT_TRUE(lease);
+        lease->cltt_ -= delay;
+        lease->current_cltt_ -= delay;
+        if (reclaim) {
+            lease->state_ = Lease::STATE_EXPIRED_RECLAIMED;
+        }
+        auto& lease_mgr = LeaseMgrFactory::instance();
+        if (update) {
+            EXPECT_NO_THROW(lease_mgr.updateLease6(lease));
+        } else {
+            EXPECT_TRUE(lease_mgr.addLease(lease));
+        }
+    }
+
+    /// @brief Interface Manager's fake configuration control.
+    IfaceMgrTestConfig iface_mgr_test_config_;
+};
+
+// Test allocation with empty pool.
+TEST_F(FLQTest, empty) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Perform 4-way exchange with the server requesting the last prefix.
+    client.requestPrefix(1, 51, IOAddress("2001:db8:1:e000::"));
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config preferred-lifetime (200).
+    // Valid lifetime should be the config valid-lifetime (600).
+    checkResponse(lease, 200, 600);
+}
+
+// Test allocation with almost full pool.
+TEST_F(FLQTest, last) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Create leases for the first prefixes.
+    fill();
+
+    // Perform 4-way exchange with the server.
+    client.requestPrefix();
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config min-preferred-lifetime (100).
+    // Valid lifetime should be the config min-valid-lifetime (400).
+    checkResponse(lease, 100, 400);
+}
+
+// Test allocation with an expired lease.
+TEST_F(FLQTest, expired) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Create leases for the first prefixes.
+    fill();
+
+    // Create and expire last lease.
+    auto lease7 = createLease6(IOAddress("2001:db8:1:e000::"), 8);
+    ageLease(lease7, 10000, false);
+    ASSERT_TRUE(lease7->expired());
+
+    // Perform 4-way exchange with the server.
+    client.requestPrefix();
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config min-preferred-lifetime (100).
+    // Valid lifetime should be the config min-valid-lifetime (400).
+    checkResponse(lease, 100, 400);
+}
+
+// Test allocation with a reclaimed lease.
+TEST_F(FLQTest, reclaimed) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Create leases for the first prefixes.
+    fill();
+
+    // Create and reclaim last lease.
+    auto lease7 = createLease6(IOAddress("2001:db8:1:e000::"), 8);
+    ageLease(lease7, 10000, false, true);
+    ASSERT_TRUE(lease7->expired());
+
+    // Perform 4-way exchange with the server.
+    client.requestPrefix();
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config min-preferred-lifetime (100).
+    // Valid lifetime should be the config min-valid-lifetime (400).
+    checkResponse(lease, 100, 400);
+}
+
+// Test renewal with almost empty pool.
+TEST_F(FLQTest, renew) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Perform 4-way exchange with the server requesting the last prefix.
+    client.requestPrefix(1, 51, IOAddress("2001:db8:1:e000::"));
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config preferred-lifetime (200).
+    // Valid lifetime should be the config valid-lifetime (600).
+    checkResponse(lease, 200, 600);
+
+    // Age the lease.
+    ageLease(lease, 1000, true);
+
+    // Send the renew message to the server.
+    ASSERT_NO_THROW(client.doRenew());
+
+    // Server should have renewed the prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr renewed = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config preferred-lifetime (200).
+    // Valid lifetime should be the config valid-lifetime (600).
+    checkResponse(renewed, 200, 600);
+
+    // Check the lease was updated.
+    EXPECT_NEAR(lease->cltt_ + 1000, renewed->cltt_, 2);
+}
+
+// Test renewal with full pool.
+TEST_F(FLQTest, renewFull) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Perform 4-way exchange with the server requesting the last prefix.
+    client.requestPrefix(1, 51, IOAddress("2001:db8:1:e000::"));
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config preferred-lifetime (200).
+    // Valid lifetime should be the config valid-lifetime (600).
+    checkResponse(lease, 200, 600);
+
+    // Create leases for the first prefixes.
+    fill();
+
+    // Age the lease.
+    ageLease(lease, 1000, true);
+
+    // Send the renew message to the server.
+    ASSERT_NO_THROW(client.doRenew());
+
+    // Server should have renewed the prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr renewed = checkLease(client.getLease(0));
+    ASSERT_TRUE(renewed);
+
+    // Preferred lifetime should be the config min-preferred-lifetime (100).
+    // Valid lifetime should be the config min-valid-lifetime (400).
+    checkResponse(renewed, 100, 400);
+
+    // Check the lease was updated.
+    EXPECT_NEAR(lease->cltt_ + 1000, renewed->cltt_, 2);
+}
+
+// Test renewal with full pool but remaining lifetimes greater than minimal.
+TEST_F(FLQTest, renewRemaining) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Perform 4-way exchange with the server requesting the last prefix.
+    client.requestPrefix(1, 51, IOAddress("2001:db8:1:e000::"));
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config preferred-lifetime (200).
+    // Valid lifetime should be the config valid-lifetime (600).
+    checkResponse(lease, 200, 600);
+
+    // Create leases for the first prefixes.
+    fill();
+
+    // Age the lease but only by 50 seconds.
+    ageLease(lease, 50, true);
+
+    // Send the renew message to the server.
+    ASSERT_NO_THROW(client.doRenew());
+
+    // Server should have renewed the prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr renewed = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the remaining lifetime so ~150.
+    // Valid lifetime should be the remaining lifetime so ~550
+    checkResponse(renewed, 150, 550, true, true);
+
+    // Check the lease was updated.
+    EXPECT_NEAR(lease->cltt_ + 50, renewed->cltt_, 2);
+}
+
+// Test renewal with full pool but remaining valid lifetime only greater
+// than minimal.
+TEST_F(FLQTest, renewRemainingValid) {
+    Dhcp6Client client(srv_);
+
+    // Configure DHCP server.
+    configure(FLQ_CONFIG, *client.getServer());
+
+    // Perform 4-way exchange with the server requesting the last prefix.
+    client.requestPrefix(1, 51, IOAddress("2001:db8:1:e000::"));
+    ASSERT_NO_THROW(client.doSARR());
+
+    // Server should have assigned a prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr lease = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config preferred-lifetime (200).
+    // Valid lifetime should be the config valid-lifetime (600).
+    checkResponse(lease, 200, 600);
+
+    // Create leases for the first prefixes.
+    fill();
+
+    // Age the lease but only by 150 seconds.
+    ageLease(lease, 150, true);
+
+    // Send the renew message to the server.
+    ASSERT_NO_THROW(client.doRenew());
+
+    // Server should have renewed the prefix.
+    ASSERT_EQ(1, client.getLeaseNum());
+    Lease6Ptr renewed = checkLease(client.getLease(0));
+
+    // Preferred lifetime should be the config min-preferred-lifetime (100).
+    // Valid lifetime should be the remaining lifetime so ~450
+    checkResponse(renewed, 100, 450, false, true);
+
+    // Check the lease was updated.
+    EXPECT_NEAR(lease->cltt_ + 150, renewed->cltt_, 2);
+}
+
+}

src/bin/dhcp6/tests/meson.build

@@ -127,6 +127,7 @@ kea_dhcp6_tests = executable(
     'dhcp6_test_utils.cc',
     'dhcp6_unittests.cc',
     'dhcp6to4_ipc_unittest.cc',
+    'flq_unittest.cc',
     'fqdn_unittest.cc',
     'get_config_unittest.cc',
     'hooks_unittest.cc',

src/lib/asiolink/io_service.cc

@@ -69,7 +69,7 @@ public:
     /// false this indicates that the IOService was stopped.
     ///
     /// @param wait_time_usecs wait time in microseconds.
-    /// @param[out] time_out set to true if the wait time expired
+    /// @param[out] timed_out set to true if the wait time expired
     /// without any handlers executing.
     /// timed_out parameter will be set true if the wait time elapsed.
     ///

src/lib/asiolink/io_service.h

@@ -70,7 +70,7 @@ public:
     /// false this indicates that the IOService was stopped.
     ///
     /// @param wait_time_usecs wait time in microseconds.
-    /// @param[out] time_out set to true if the wait time expired
+    /// @param[out] timed_out set to true if the wait time expired
     /// without any handlers executing.
     /// timed_out parameter will be set true if the wait time elapsed.
     ///

src/lib/dhcp/classify.h

@@ -272,7 +272,7 @@ private:
 /// their hashes are equal, if two class lists are not equal their hashes
 /// are almost surely not equal.
 ///
-/// @param address A @c ClientClasses to hash.
+/// @param client_classes A @c ClientClasses to hash.
 /// @return The hash of the ClientClasses.
 
 size_t hash_value(const ClientClasses& client_classes);

src/lib/dhcpsrv/alloc_engine.cc

@@ -1737,6 +1737,22 @@ AllocEngine::removeNonreservedLeases6(ClientContext6& ctx,
         existing_leases.end(), Lease6Ptr()), existing_leases.end());
 }
 
+namespace {
+bool
+useMinLifetimes6(AllocEngine::ClientContext6& ctx, const IOAddress& addr,
+                 uint8_t prefix_len) {
+    auto const& threshold = ctx.subnet_->getAdaptiveLeaseTimeThreshold();
+    if (!threshold.unspecified() && (threshold < 1.0)) {
+        auto const& occupancy = ctx.subnet_->getAllocator(Lease::TYPE_PD)->
+            getOccupancyRate(addr, prefix_len, ctx.query_->getClasses());
+        if (occupancy >= threshold) {
+            return (true);
+        }
+    }
+    return (false);
+}
+} // end of anonymous namespace.
+
 Lease6Ptr
 AllocEngine::reuseExpiredLease(Lease6Ptr& expired, ClientContext6& ctx,
                                uint8_t prefix_len,
@@ -1764,12 +1780,20 @@ AllocEngine::reuseExpiredLease(Lease6Ptr& expired, ClientContext6& ctx,
     // address, lease type and prefixlen (0) stay the same
     expired->iaid_ = ctx.currentIA().iaid_;
     expired->duid_ = ctx.duid_;
+    expired->hwaddr_ = ctx.hwaddr_;
 
     // Calculate life times.
-    getLifetimes6(ctx, expired->preferred_lft_, expired->valid_lft_);
+    expired->preferred_lft_ = 0;
+    expired->valid_lft_ = 0;
+    if ((expired->type_ == Lease::TYPE_PD) &&
+        useMinLifetimes6(ctx, expired->addr_, prefix_len)) {
+        getMinLifetimes6(ctx, expired->preferred_lft_, expired->valid_lft_);
+    } else {
+        getLifetimes6(ctx, expired->preferred_lft_, expired->valid_lft_);
+    }
     expired->reuseable_valid_lft_ = 0;
 
-    expired->cltt_ = time(NULL);
+    expired->cltt_ = time(0);
     expired->subnet_id_ = ctx.subnet_->getID();
     expired->hostname_ = ctx.hostname_;
     expired->fqdn_fwd_ = ctx.fwd_dns_update_;
@@ -1891,6 +1915,20 @@ AllocEngine::reuseExpiredLease(Lease6Ptr& expired, ClientContext6& ctx,
     return (expired);
 }
 
+namespace {
+void sanitizeLifetimes6(AllocEngine::ClientContext6& ctx,
+                        uint32_t& preferred, uint32_t& valid) {
+    // If preferred isn't set or insane, calculate it as valid_lft * 0.625.
+    if (!preferred || preferred > valid) {
+        preferred = ((valid * 5)/8);
+        LOG_DEBUG(alloc_engine_logger, ALLOC_ENGINE_DBG_TRACE,
+                  ALLOC_ENGINE_V6_CALCULATED_PREFERRED_LIFETIME)
+                .arg(ctx.query_->getLabel())
+                .arg(preferred);
+    }
+}
+} // end of anonymous namespace.
+
 void
 AllocEngine::getLifetimes6(ClientContext6& ctx, uint32_t& preferred, uint32_t& valid) {
     // If the triplets are specified in one of our classes use it.
@@ -1950,14 +1988,70 @@ AllocEngine::getLifetimes6(ClientContext6& ctx, uint32_t& preferred, uint32_t& v
         }
     }
 
-    // If preferred isn't set or insane, calculate it as valid_lft * 0.625.
-    if (!preferred || preferred > valid) {
-        preferred = ((valid * 5)/8);
-        LOG_DEBUG(alloc_engine_logger, ALLOC_ENGINE_DBG_TRACE,
-                  ALLOC_ENGINE_V6_CALCULATED_PREFERRED_LIFETIME)
-                .arg(ctx.query_->getLabel())
-                .arg(preferred);
+    sanitizeLifetimes6(ctx, preferred, valid);
+}
+
+void
+AllocEngine::getMinLifetimes6(ClientContext6& ctx, uint32_t& preferred,
+                              uint32_t& valid) {
+    // If the triplets are specified in one of our classes use it.
+    // We use the first one we find for each lifetime.
+    Triplet<uint32_t> candidate_preferred;
+    Triplet<uint32_t> candidate_valid;
+    const ClientClasses classes = ctx.query_->getClasses();
+    if (!classes.empty()) {
+        // Let's get class definitions
+        const ClientClassDictionaryPtr& dict =
+            CfgMgr::instance().getCurrentCfg()->getClientClassDictionary();
+
+        // Iterate over the assigned class definitions.
+        int have_both = 0;
+        for (auto const& name : classes) {
+            ClientClassDefPtr cl = dict->findClass(name);
+            if (candidate_preferred.unspecified() &&
+                (cl && (!cl->getPreferred().unspecified()))) {
+                candidate_preferred = cl->getPreferred();
+                ++have_both;
+            }
+
+            if (candidate_valid.unspecified() &&
+                (cl && (!cl->getValid().unspecified()))) {
+                candidate_valid = cl->getValid();
+                ++have_both;
+            }
+            if (have_both == 2) {
+                break;
+            }
+        }
     }
+
+    // If no classes specified preferred lifetime, get it from the subnet.
+    if (!candidate_preferred) {
+        candidate_preferred = ctx.subnet_->getPreferred();
+    }
+
+    // If no classes specified valid lifetime, get it from the subnet.
+    if (!candidate_valid) {
+        candidate_valid = ctx.subnet_->getValid();
+    }
+
+    // Save remaining values.
+    uint32_t remain_preferred(preferred);
+    uint32_t remain_valid(valid);
+
+    // Set the outbound parameters to the minimal values.
+    preferred = candidate_preferred.getMin();
+    valid = candidate_valid.getMin();
+
+    // Return at least the remaining values.
+    if (remain_preferred > preferred) {
+        preferred = remain_preferred;
+    }
+    if (remain_valid > valid) {
+        valid = remain_valid;
+    }
+
+    sanitizeLifetimes6(ctx, preferred, valid);
 }
 
 Lease6Ptr AllocEngine::createLease6(ClientContext6& ctx,
@@ -1971,7 +2065,12 @@ Lease6Ptr AllocEngine::createLease6(ClientContext6& ctx,
 
     uint32_t preferred = 0;
     uint32_t valid = 0;
-    getLifetimes6(ctx, preferred, valid);
+    if ((ctx.currentIA().type_ == Lease::TYPE_PD) &&
+        useMinLifetimes6(ctx, addr, prefix_len)) {
+        getMinLifetimes6(ctx, preferred, valid);
+    } else {
+        getLifetimes6(ctx, preferred, valid);
+    }
 
     Lease6Ptr lease(new Lease6(ctx.currentIA().type_, addr, ctx.duid_,
                                ctx.currentIA().iaid_, preferred,
@@ -2098,6 +2197,31 @@ Lease6Ptr AllocEngine::createLease6(ClientContext6& ctx,
     }
 }
 
+void
+AllocEngine::getRemaining(const Lease6Ptr& lease, uint32_t& preferred,
+                          uint32_t& valid) {
+    valid = 0;
+    preferred = 0;
+    if (!lease || (lease->state_ != Lease::STATE_DEFAULT)) {
+        return;
+    }
+    time_t now = time(0);
+    // Refuse time not going forward.
+    if (lease->cltt_ > now) {
+        return;
+    }
+    uint32_t age = now - lease->cltt_;
+    // Already expired.
+    if (age >= lease->valid_lft_) {
+        return;
+    }
+    valid = lease->valid_lft_ - age;
+    if (age >= lease->preferred_lft_) {
+        return;
+    }
+    preferred = lease->preferred_lft_ - age;
+}
+
 Lease6Collection
 AllocEngine::renewLeases6(ClientContext6& ctx) {
     try {
@@ -2282,7 +2406,17 @@ AllocEngine::extendLease6(ClientContext6& ctx, Lease6Ptr lease) {
 
     // Calculate life times.
     uint32_t current_preferred_lft = lease->preferred_lft_;
-    getLifetimes6(ctx, lease->preferred_lft_, lease->valid_lft_);
+    if ((lease->type_ == Lease::TYPE_PD) &&
+        useMinLifetimes6(ctx, lease->addr_, lease->prefixlen_)) {
+        uint32_t remain_preferred_lft(0);
+        uint32_t remain_valid_lft(0);
+        getRemaining(lease, remain_preferred_lft, remain_valid_lft);
+        lease->preferred_lft_ = remain_preferred_lft;
+        lease->valid_lft_ = remain_valid_lft;
+        getMinLifetimes6(ctx, lease->preferred_lft_, lease->valid_lft_);
+    } else {
+        getLifetimes6(ctx, lease->preferred_lft_, lease->valid_lft_);
+    }
 
     // If either has changed set the changed flag.
     if ((lease->preferred_lft_ != current_preferred_lft) ||
@@ -2468,7 +2602,13 @@ AllocEngine::updateLeaseData(ClientContext6& ctx, const Lease6Collection& leases
         uint32_t current_preferred_lft = lease->preferred_lft_;
         if (lease->valid_lft_ == 0) {
             // The lease was expired by a release: reset zero lifetimes.
-            getLifetimes6(ctx, lease->preferred_lft_, lease->valid_lft_);
+            lease->preferred_lft_ = 0;
+            if ((lease->type_ == Lease::TYPE_PD) &&
+                useMinLifetimes6(ctx, lease->addr_, lease->prefixlen_)) {
+                getMinLifetimes6(ctx, lease->preferred_lft_, lease->valid_lft_);
+            } else {
+                getLifetimes6(ctx, lease->preferred_lft_, lease->valid_lft_);
+            }
         }
         if (!ctx.fake_allocation_) {
             bool update_stats = false;
@@ -4313,6 +4453,65 @@ AllocEngine::getValidLft(const ClientContext4& ctx) {
     return (candidate_lft.get());
 }
 
+void
+AllocEngine::getMinValidLft(const ClientContext4& ctx, uint32_t& valid) {
+    // If it's BOOTP, use infinite valid lifetime.
+    if (ctx.query_->inClass("BOOTP")) {
+        valid = Lease::INFINITY_LFT;
+        return;
+    }
+
+    // If the triplet is specified in one of our classes use it.
+    // We use the first one we find.
+    Triplet<uint32_t> candidate_lft;
+    const ClientClasses classes = ctx.query_->getClasses();
+    if (!classes.empty()) {
+        // Let's get class definitions
+        const ClientClassDictionaryPtr& dict =
+            CfgMgr::instance().getCurrentCfg()->getClientClassDictionary();
+
+        // Iterate over the assigned class definitions.
+        for (auto const& name : classes) {
+            ClientClassDefPtr cl = dict->findClass(name);
+            if (cl && (!cl->getValid().unspecified())) {
+                candidate_lft = cl->getValid();
+                break;
+            }
+        }
+    }
+
+    // If no classes specified it, get it from the subnet.
+    if (!candidate_lft) {
+        candidate_lft = ctx.subnet_->getValid();
+    }
+
+    // Save remaining value.
+    uint32_t remain(valid);
+
+    // Set to the minimal value.
+    valid = candidate_lft.getMin();
+
+    // Return at least the remaining value.
+    if (remain > valid) {
+        valid = remain;
+    }
+}
+
+namespace {
+bool
+useMinValidLft(const AllocEngine::ClientContext4& ctx, const IOAddress&addr) {
+    auto const& threshold = ctx.subnet_->getAdaptiveLeaseTimeThreshold();
+    if (!threshold.unspecified() && (threshold < 1.0)) {
+        auto const& occupancy = ctx.subnet_->getAllocator(Lease::TYPE_V4)->
+            getOccupancyRate(addr, ctx.query_->getClasses());
+        if (occupancy >= threshold) {
+            return (true);
+        }
+    }
+    return (false);
+}
+} // end of anonymous namespace.
+
 Lease4Ptr
 AllocEngine::createLease4(const ClientContext4& ctx, const IOAddress& addr,
                           CalloutHandle::CalloutNextStep& callout_status) {
@@ -4324,9 +4523,16 @@ AllocEngine::createLease4(const ClientContext4& ctx, const IOAddress& addr,
     }
 
     // Get the context appropriate lifetime.
-    uint32_t valid_lft = (ctx.offer_lft_ ? ctx.offer_lft_ : getValidLft(ctx));
+    uint32_t valid_lft = ctx.offer_lft_;
+    if (!valid_lft) {
+        if (useMinValidLft(ctx, addr)) {
+            getMinValidLft(ctx, valid_lft);
+        } else {
+            valid_lft = getValidLft(ctx);
+        }
+    }
 
-    time_t now = time(NULL);
+    time_t now = time(0);
 
     ClientIdPtr client_id;
     if (ctx.subnet_->getMatchClientId()) {
@@ -4457,6 +4663,30 @@ AllocEngine::createLease4(const ClientContext4& ctx, const IOAddress& addr,
     }
 }
 
+void
+AllocEngine::getRemaining(const Lease4Ptr& lease, uint32_t& valid) {
+    valid = 0;
+    if (!lease || (lease->state_ != Lease::STATE_DEFAULT)) {
+        return;
+    }
+    // Always remain infinite lifetime leases.
+    if (lease->valid_lft_ == Lease::INFINITY_LFT) {
+        valid = Lease::INFINITY_LFT;
+        return;
+    }
+    time_t now = time(0);
+    // Refuse time not going forward.
+    if (lease->cltt_ > now) {
+        return;
+    }
+    uint32_t age = now - lease->cltt_;
+    // Already expired.
+    if (age >= lease->valid_lft_) {
+        return;
+    }
+    valid = lease->valid_lft_ - age;
+}
+
 Lease4Ptr
 AllocEngine::renewLease4(const Lease4Ptr& lease,
                          AllocEngine::ClientContext4& ctx) {
@@ -4998,10 +5228,20 @@ AllocEngine::updateLease4Information(const Lease4Ptr& lease,
         changed = true;
         lease->client_id_ = ClientIdPtr();
     }
-    lease->cltt_ = time(NULL);
+    uint32_t remain_lft(0);
+    getRemaining(lease, remain_lft);
+    lease->cltt_ = time(0);
 
     // Get the context appropriate valid lifetime.
-    lease->valid_lft_ = (ctx.offer_lft_ ? ctx.offer_lft_ : getValidLft(ctx));
+    lease->valid_lft_ = ctx.offer_lft_;
+    if (!lease->valid_lft_) {
+        if (useMinValidLft(ctx, lease->addr_)) {
+            lease->valid_lft_ = remain_lft;
+            getMinValidLft(ctx, lease->valid_lft_);
+        } else {
+            lease->valid_lft_ = getValidLft(ctx);
+        }
+    }
 
     // Valid lifetime has changed.
     if (lease->valid_lft_ != lease->current_valid_lft_) {

src/lib/dhcpsrv/alloc_engine.h

@@ -816,10 +816,26 @@ public:
     ///
     /// @param ctx client context that passes all necessary information. See
     ///        @ref ClientContext6 for details.
-    /// @param [out] preferred set to the preferred lifetime that should be used.
-    /// @param [out] valid set to the valid lifetime that should be used.
+    /// @param[out] preferred set to the preferred lifetime that should be used.
+    /// @param[out] valid set to the valid lifetime that should be used.
     static void getLifetimes6(ClientContext6& ctx, uint32_t& preferred,
                               uint32_t& valid);
+
+    /// @brief Determines the preferred and valid v6 lease lifetimes when
+    /// the pool occupancy is over the adaptive lease time threshold.
+    ///
+    /// As for the common case find the candidate triplet and return
+    /// minimal values. Requested lifetimes are ignored but remaining
+    /// lifetimes are returned when greater than minimal.
+    ///
+    /// @param ctx client context that passes all necessary information. See
+    ///        @ref ClientContext6 for details.
+    /// @param[in,out] preferred set to the preferred lifetime that should
+    ///                be used. Caller must set it to 0 or remaining value.
+    /// @param[in,out] valid set to the valid lifetime that should be used.
+    ///                Caller must set it to 0 or remaining value.
+    static void getMinLifetimes6(ClientContext6& ctx, uint32_t& preferred,
+                                 uint32_t& valid);
 private:
 
     /// @brief Creates a lease and inserts it in LeaseMgr if necessary
@@ -834,7 +850,7 @@ private:
     ///        available
     /// @param prefix_len length of the prefix (for PD only)
     ///        should be 128 for other lease types
-    /// @param [out] callout_status callout returned by the lease6_select
+    /// @param[out] callout_status callout returned by the lease6_select
     ///
     /// The following fields of the ctx structure are used:
     /// @ref ClientContext6::subnet_ Subnet the lease is allocated from
@@ -1537,6 +1553,21 @@ public:
     /// @return unsigned integer value of the valid lifetime to use.
     static uint32_t getValidLft(const ClientContext4& ctx);
 
+    /// @brief Returns the valid lifetime based on the v4 context when
+    /// the pool occupancy is over the adaptive lease time threshold.
+    ///
+    /// If the client query is a BOOTP query, the value returned will
+    /// be Lease::INFINITY_LFT.
+    ///
+    /// Otherwise, as for the common case find the canndidate triplet
+    /// and return the minimal value. Requested lifetime is ignored but
+    /// remaining lifetime is returned when greater than minimal.
+    ///
+    /// @param ctx Client context holding various information about the client.
+    /// @param[in,out] valid set to the valid lifetime that should be used.
+    ///                Caller must set it to 0 or remaining value.
+    static void getMinValidLft(const ClientContext4& ctx, uint32_t& valid);
+
     /// @brief Returns the offer lifetime based on the v4 context
     ///
     /// If the client query is a BOOTP query or something other than
@@ -1555,6 +1586,20 @@ public:
     /// @return unsigned integer value of the offer lifetime to use.
     static uint32_t getOfferLft(const ClientContext4& ctx,
                                 bool only_on_discover = true);
+    /// @brief Set remaining valid life time.
+    ///
+    /// @param lease A pointer to the lease.
+    /// @param [out] valid The remaining valid life time or 0.
+    static void getRemaining(const Lease4Ptr& lease, uint32_t& valid);
+
+    /// @brief Set remaining valid and preferred life times.
+    ///
+    /// @param lease A pointer to the lease.
+    /// @param [out] preferred The remaining preferred life time or 0.
+    /// @param [out] valid The remaining valid life time or 0.
+    static void getRemaining(const Lease6Ptr& lease, uint32_t& preferred,
+                             uint32_t& valid);
+
 private:
 
     /// @brief Offers the lease.

src/lib/dhcpsrv/allocator.cc

@@ -78,5 +78,18 @@ Allocator::initAfterConfigure() {
     inited_ = true;
 }
 
+double
+Allocator::getOccupancyRate(const asiolink::IOAddress&,
+                            const ClientClasses&) const {
+    return (0.);
+}
+
+double
+Allocator::getOccupancyRate(const asiolink::IOAddress&,
+                            const uint8_t,
+                            const ClientClasses&) const {
+    return (0.);
+}
+
 }
 }

src/lib/dhcpsrv/allocator.h

@@ -140,6 +140,36 @@ public:
                                    hint_prefix_length));
     }
 
+    /// @brief Returns the occupancy rate (v4 addresses).
+    ///
+    /// The method counts the total number and the number of not free
+    /// addresses in the suitable pools of the subnet, and returns the
+    /// occupancy rate. If the total number of addresses is over UMAX64
+    /// or the address is not from one of these pools, or by default
+    /// the 0. rate is returned.
+    ///
+    /// @param addr the address.
+    /// @param client_classes list of classes client belongs to.
+    virtual double
+    getOccupancyRate(const asiolink::IOAddress& addr,
+                     const ClientClasses& client_classes) const;
+
+    /// @brief Returns the occupancy rate (v6 prefixes).
+    ///
+    /// The method counts the total number and the number of not free
+    /// prefixes in the suitable pools of the subnet, and returns the
+    /// occupancy rate. If the total number of prefixes is over UMAX64
+    /// or the prefix is not from one of these pools, or by default
+    /// the 0. rate is returned.
+    ///
+    /// @param pref the prefix.
+    /// @param plen the prefix length.
+    /// @param client_classes list of classes client belongs to.
+    virtual double
+    getOccupancyRate(const asiolink::IOAddress& pref,
+                     const uint8_t plen,
+                     const ClientClasses& client_classes) const;
+
     /// @brief Check if the pool matches the selection criteria relative to the
     /// provided hint prefix length.
     ///

src/lib/dhcpsrv/cfg_globals.cc

@@ -61,6 +61,7 @@ CfgGlobals::nameToIndex = {
     { "ddns-ttl-min", DDNS_TTL_MIN },
     { "ddns-ttl-max", DDNS_TTL_MAX },
     { "host-reservation-identifiers", HOST_RESERVATION_IDENTIFIERS },
+    { "adaptive-lease-time-threshold", ADAPTIVE_LEASE_TIME_THRESHOLD },
 
     // DHCPv4 specific parameters.
     { "echo-client-id", ECHO_CLIENT_ID },

src/lib/dhcpsrv/cfg_globals.h

@@ -84,6 +84,7 @@ public:
         DDNS_TTL_MIN,
         DDNS_TTL_MAX,
         HOST_RESERVATION_IDENTIFIERS,
+        ADAPTIVE_LEASE_TIME_THRESHOLD,
 
         // DHCPv4 specific parameters.
         ECHO_CLIENT_ID,

src/lib/dhcpsrv/cfg_hosts.h

@@ -840,7 +840,7 @@ private:
     /// @return Collection of const @c Host objects.
     ConstHostCollection
     getAllInternal4(const SubnetID& subnet_id,
-		    const asiolink::IOAddress& address) const;
+                    const asiolink::IOAddress& address) const;
 
     /// @brief Returns @c Host objects for the specified (Subnet-id,IPv6 address) tuple.
     ///

src/lib/dhcpsrv/cfg_option.h

@@ -904,7 +904,7 @@ public:
     /// @return A pointer to the unparsed configuration.
     isc::data::ElementPtr
     toElementWithMetadata(const bool include_metadata,
-			  CfgOptionDefPtr cfg_option_def = CfgOptionDefPtr()) const;
+                          CfgOptionDefPtr cfg_option_def = CfgOptionDefPtr()) const;
 
 private:
 

src/lib/dhcpsrv/database_backends.dox

@@ -155,7 +155,7 @@
     example: 0
 
   - <b>fqdn_rev</b> - FQDN reverse DNS RR update flag \n
-    type: bool (0 or 1)	\n
+    type: bool (0 or 1) \n
     example: 1
 
   - <b>hostname</b> - hostname \n

src/lib/dhcpsrv/flq_allocation_state.cc

@@ -53,6 +53,17 @@ PoolFreeLeaseQueueAllocationState::deleteFreeLease(const asiolink::IOAddress& ad
     }
 }
 
+bool
+PoolFreeLeaseQueueAllocationState::isFreeLease(const asiolink::IOAddress& address) const {
+    if (free_lease4_queue_) {
+        auto const& idx = free_lease4_queue_->get<1>();
+        return (idx.count(address.toUint32()) > 0);
+    } else {
+        auto const& idx = free_lease6_queue_->get<1>();
+        return (idx.count(address) > 0);
+    }
+}
+
 IOAddress
 PoolFreeLeaseQueueAllocationState::offerFreeLease() {
     if (free_lease4_queue_) {
@@ -84,4 +95,3 @@ PoolFreeLeaseQueueAllocationState::getFreeLeaseCount() const {
 
 } // end of namespace isc::dhcp
 } // end of namespace isc
-

src/lib/dhcpsrv/flq_allocation_state.h

@@ -55,6 +55,11 @@ public:
     /// @param address lease address.
     void deleteFreeLease(const asiolink::IOAddress& address);
 
+    /// @brief Check if a lease is in the queue.
+    ///
+    /// @param address lease address.
+    bool isFreeLease(const asiolink::IOAddress& address) const;
+
     /// @brief Returns next available lease.
     ///
     /// @return next free lease address or IPv4/IPv6 zero address when

src/lib/dhcpsrv/flq_allocator.cc

@@ -13,6 +13,7 @@
 #include <dhcpsrv/lease_mgr_factory.h>
 #include <dhcpsrv/subnet.h>
 #include <util/stopwatch.h>
+#include <limits>
 #include <unordered_set>
 
 using namespace isc::asiolink;
@@ -134,6 +135,105 @@ FreeLeaseQueueAllocator::pickPrefixInternal(const ClientClasses& client_classes,
     return (IOAddress::IPV6_ZERO_ADDRESS());
 }
 
+double
+FreeLeaseQueueAllocator::getOccupancyRate(const IOAddress& addr,
+                                          const ClientClasses& client_classes) const {
+    // Sanity.
+    if (!addr.isV4()) {
+        return (0.);
+    }
+    auto subnet = subnet_.lock();
+    uint128_t total(0);
+    uint128_t busy(0);
+    bool found(false);
+
+    for (auto const& pool : subnet->getPools(Lease::TYPE_V4)) {
+        if (!pool->clientSupported(client_classes)) {
+            continue;
+        }
+        uint128_t capacity = pool->getCapacity();
+        total += capacity;
+        if (total >= std::numeric_limits<uint64_t>::max()) {
+            return (0.);
+        }
+        auto pool_state = boost::dynamic_pointer_cast<PoolFreeLeaseQueueAllocationState>(pool->getAllocationState());
+        if (!pool_state) {
+            continue;
+        }
+        uint128_t free_cnt = pool_state->getFreeLeaseCount();
+        if (!found && pool->inRange(addr)) {
+            found = true;
+            if ((free_cnt > 0) && pool_state->isFreeLease(addr)) {
+                --free_cnt;
+            }
+        }
+        if (free_cnt > capacity) {
+            free_cnt = capacity;
+        }
+        busy += capacity - free_cnt;
+    }
+    if (!found) {
+        return (0.);
+    }
+    // Should not happen...
+    if (total == 0) {
+        return (0.);
+    }
+    return (static_cast<double>(busy) / static_cast<double>(total));
+}
+
+double
+FreeLeaseQueueAllocator::getOccupancyRate(const IOAddress& pref,
+                                          const uint8_t plen,
+                                          const ClientClasses& client_classes) const {
+    // Sanity.
+    if (!pref.isV6()) {
+        return (0.);
+    }
+    auto subnet = subnet_.lock();
+    uint128_t total(0);
+    uint128_t busy(0);
+    bool found(false);
+
+    for (auto const& pool : subnet->getPools(Lease::TYPE_PD)) {
+        if (!pool->clientSupported(client_classes)) {
+            continue;
+        }
+        auto const& pool6 = boost::dynamic_pointer_cast<Pool6>(pool);
+        if (!pool6 || (pool6->getLength() > plen)) {
+            continue;
+        }
+        uint128_t capacity = pool->getCapacity();
+        total += capacity;
+        if (total >= std::numeric_limits<uint64_t>::max()) {
+            return (0.);
+        }
+        auto pool_state = boost::dynamic_pointer_cast<PoolFreeLeaseQueueAllocationState>(pool->getAllocationState());
+        if (!pool_state) {
+            continue;
+        }
+        uint128_t free_cnt = pool_state->getFreeLeaseCount();
+        if (!found && pool->inRange(pref)) {
+            found = true;
+            if ((free_cnt > 0) && pool_state->isFreeLease(pref)) {
+                --free_cnt;
+            }
+        }
+        if (free_cnt > capacity) {
+            free_cnt = capacity;
+        }
+        busy += capacity - free_cnt;
+    }
+    if (!found) {
+        return (0.);
+    }
+    // Should not happen...
+    if (total == 0) {
+        return (0.);
+    }
+    return (static_cast<double>(busy) / static_cast<double>(total));
+}
+
 void
 FreeLeaseQueueAllocator::initAfterConfigureInternal() {
     auto subnet = subnet_.lock();

src/lib/dhcpsrv/flq_allocator.h

@@ -51,6 +51,36 @@ public:
         return ("flq");
     }
 
+    /// @brief Returns the occupancy rate (v4 addresses).
+    ///
+    /// The method counts the total number and the number of not free
+    /// addresses in the suitable pools of the subnet, and returns the
+    /// occupancy rate. If the total number of addresses is over UMAX64
+    /// or the address is not from one of these pools, or by default
+    /// the 0. rate is returned.
+    ///
+    /// @param addr the address.
+    /// @param client_classes list of classes client belongs to.
+    virtual double
+    getOccupancyRate(const asiolink::IOAddress& addr,
+                     const ClientClasses& client_classes) const;
+
+    /// @brief Returns the occupancy rate (v6 prefixes).
+    ///
+    /// The method counts the total number and the number of not free
+    /// prefixes in the suitable pools of the subnet, and returns the
+    /// occupancy rate. If the total number of prefixes is over UMAX64
+    /// or the prefix is not from one of these pools, or by default
+    /// the 0. rate is returned.
+    ///
+    /// @param pref the prefix.
+    /// @param plen the prefix length.
+    /// @param client_classes list of classes client belongs to.
+    virtual double
+    getOccupancyRate(const asiolink::IOAddress& pref,
+                     const uint8_t plen,
+                     const ClientClasses& client_classes) const;
+
 private:
 
     /// @brief Performs allocator initialization after server's reconfiguration.

src/lib/dhcpsrv/network.cc

@@ -276,6 +276,11 @@ Network::toElement() const {
         map->set("allocator", Element::create(allocator_type_));
     }
 
+    if (!adaptive_lease_time_threshold_.unspecified()) {
+        map->set("adaptive-lease-time-threshold",
+                 Element::create(adaptive_lease_time_threshold_));
+    }
+
     return (map);
 }
 

src/lib/dhcpsrv/network.h

@@ -221,7 +221,8 @@ public:
           cache_threshold_(), cache_max_age_(), ddns_update_on_renew_(),
           ddns_conflict_resolution_mode_(), ddns_ttl_percent_(),
           ddns_ttl_(), ddns_ttl_min_(), ddns_ttl_max_(),
-          allocator_type_(), default_allocator_type_() {
+          allocator_type_(), default_allocator_type_(),
+          adaptive_lease_time_threshold_() {
     }
 
     /// @brief Virtual destructor.
@@ -894,6 +895,25 @@ public:
         default_allocator_type_ = allocator_type;
     }
 
+    /// @brief Returns percentage of the adaptive lease time threshold,
+    ///
+    /// @param inheritance inheritance mode to be used.
+    util::Optional<double>
+    getAdaptiveLeaseTimeThreshold(const Inheritance& inheritance = Inheritance::ALL) const {
+        return (getProperty<Network>(&Network::getAdaptiveLeaseTimeThreshold,
+                                     adaptive_lease_time_threshold_,
+                                     inheritance,
+                                     CfgGlobals::ADAPTIVE_LEASE_TIME_THRESHOLD));
+    }
+
+    /// @brief Sets new percentage of the adaptive lease time threshold.
+    ///
+    /// @param adaptive_lease_time_threshold New percentage to use.
+    void setAdaptiveLeaseTimeThreshold(const util::Optional<double>&
+                                       adaptive_lease_time_threshold) {
+        adaptive_lease_time_threshold_ = adaptive_lease_time_threshold;
+    }
+
     /// @brief Unparses network object.
     ///
     /// @return A pointer to unparsed network configuration.
@@ -1308,6 +1328,11 @@ protected:
     /// backend internally.
     util::Optional<std::string> default_allocator_type_;
 
+    /// @brief Percentage of the adaptive lease time threshold.
+    /// (a lease assignment over the threshold will get minimal or remaining
+    /// life times).
+    util::Optional<double> adaptive_lease_time_threshold_;
+
     /// @brief Pointer to another network that this network belongs to.
     ///
     /// The most common case is that this instance is a subnet which belongs

src/lib/dhcpsrv/parsers/base_network_parser.cc

@@ -17,7 +17,6 @@ using namespace isc::util;
 namespace isc {
 namespace dhcp {
 
-
 void
 BaseNetworkParser::parseCommon(const ConstElementPtr& network_data,
                                NetworkPtr& network) {
@@ -171,6 +170,24 @@ BaseNetworkParser::parsePdAllocatorParams(const data::ConstElementPtr& network_d
     }
 }
 
+void
+BaseNetworkParser::parseAdaptiveLeaseTimeParam(const ConstElementPtr& network_data,
+                                               NetworkPtr& network) {
+    if (network_data->contains("adaptive-lease-time-threshold")) {
+        double adaptive_lease_time_threshold =
+            getDouble(network_data, "adaptive-lease-time-threshold");
+        if ((adaptive_lease_time_threshold <= 0.0) ||
+            (adaptive_lease_time_threshold > 1.0)) {
+            isc_throw(DhcpConfigError,
+                      "adaptive-lease-time-threshold: "
+                      << adaptive_lease_time_threshold
+                      << " is invalid, it must be greater than 0.0 "
+                      << "and less than or equal to 1.0");
+        }
+        network->setAdaptiveLeaseTimeThreshold(adaptive_lease_time_threshold);
+    }
+}
+
 void
 BaseNetworkParser::parseOfferLft(const data::ConstElementPtr& network_data,
                                         Network4Ptr& network) {
@@ -251,6 +268,5 @@ BaseNetworkParser::getClientClassesElem(ConstElementPtr params,
     }
 }
 
-
 } // end of namespace isc::dhcp
 } // end of namespace isc

src/lib/dhcpsrv/parsers/base_network_parser.h

@@ -117,6 +117,21 @@ protected:
     void parsePdAllocatorParams(const data::ConstElementPtr& network_data,
                                 Network6Ptr& network);
 
+    /// @brief Parses parameter related to adaptive lease time.
+    ///
+    /// The parsed parameter is:
+    /// - adaptive-lease-time-threshold.
+    ///
+    /// @param network_data Data element holding network configuration
+    /// to be parsed.
+    /// @param [out] network Pointer to a network in which parsed data is
+    /// to be stored.
+    ///
+    /// @throw DhcpConfigError if configuration of this parameter is
+    /// invalid.
+    void parseAdaptiveLeaseTimeParam(const data::ConstElementPtr& network_data,
+                                     NetworkPtr& network);
+
     /// @brief Parses offer-lifetime parameter (v4 only)
     ///
     /// @param network_data Data element holding shared network

src/lib/dhcpsrv/parsers/dhcp_parsers.cc

@@ -972,6 +972,9 @@ Subnet4ConfigParser::initSubnet(data::ConstElementPtr params,
     // Parse lease cache parameters
     parseCacheParams(params, network);
 
+    // Parse adaptive lease time parameter.
+    parseAdaptiveLeaseTimeParam(params, network);
+
     // Set the offer_lft value for the subnet.
     if (params->contains("offer-lifetime")) {
         uint32_t offer_lft = getInteger(params, "offer-lifetime");
@@ -1441,6 +1444,9 @@ Subnet6ConfigParser::initSubnet(data::ConstElementPtr params,
 
     // Parse lease cache parameters
     parseCacheParams(params, network);
+
+    // Parse adaptive lease time parameter.
+    parseAdaptiveLeaseTimeParam(params, network);
 }
 
 void

src/lib/dhcpsrv/parsers/shared_network_parser.cc

@@ -189,6 +189,9 @@ SharedNetwork4Parser::parse(const data::ConstElementPtr& shared_network_data,
         // Parse allocator params.
         parseAllocatorParams(shared_network_data, network);
 
+        // Parse adaptive lease time parameter.
+        parseAdaptiveLeaseTimeParam(shared_network_data, network);
+
         // Parse offer-lifetime parameter.
         Network4Ptr network4 = boost::dynamic_pointer_cast<Network4>(shared_network);
         parseOfferLft(shared_network_data, network4);
@@ -368,6 +371,9 @@ SharedNetwork6Parser::parse(const data::ConstElementPtr& shared_network_data,
         auto network6 = boost::dynamic_pointer_cast<Network6>(shared_network);
         parsePdAllocatorParams(shared_network_data, network6);
 
+        // Parse adaptive lease time parameter.
+        parseAdaptiveLeaseTimeParam(shared_network_data, network);
+
     } catch (const std::exception& ex) {
         isc_throw(DhcpConfigError, ex.what() << " ("
                   << shared_network_data->getPosition() << ")");

src/lib/dhcpsrv/parsers/simple_parser4.cc

@@ -103,6 +103,7 @@ const SimpleKeywords SimpleParser4::GLOBAL4_PARAMETERS = {
     { "ddns-ttl",                         Element::integer },
     { "ddns-ttl-min",                     Element::integer },
     { "ddns-ttl-max",                     Element::integer },
+    { "adaptive-lease-time-threshold",    Element::real },
 };
 
 /// @brief This table defines default global values for DHCPv4
@@ -281,6 +282,7 @@ const SimpleKeywords SimpleParser4::SUBNET4_PARAMETERS = {
     { "ddns-ttl",                       Element::integer },
     { "ddns-ttl-min",                   Element::integer },
     { "ddns-ttl-max",                   Element::integer },
+    { "adaptive-lease-time-threshold",  Element::real },
 };
 
 /// @brief This table defines default values for each IPv4 subnet.
@@ -338,6 +340,7 @@ const ParamsList SimpleParser4::INHERIT_TO_SUBNET4 = {
     "cache-max-age",
     "allocator",
     "offer-lifetime",
+    "adaptive-lease-time-threshold",
 };
 
 /// @brief This table defines all pool parameters.
@@ -425,6 +428,7 @@ const SimpleKeywords SimpleParser4::SHARED_NETWORK4_PARAMETERS = {
     { "ddns-ttl",                       Element::integer },
     { "ddns-ttl-min",                   Element::integer },
     { "ddns-ttl-max",                   Element::integer },
+    { "adaptive-lease-time-threshold",  Element::real },
 };
 
 /// @brief This table defines default values for interfaces for DHCPv4.

src/lib/dhcpsrv/parsers/simple_parser6.cc

@@ -103,6 +103,7 @@ const SimpleKeywords SimpleParser6::GLOBAL6_PARAMETERS = {
     { "ddns-ttl",                         Element::integer },
     { "ddns-ttl-min",                     Element::integer },
     { "ddns-ttl-max",                     Element::integer },
+    { "adaptive-lease-time-threshold",    Element::real },
 };
 
 /// @brief This table defines default global values for DHCPv6
@@ -274,6 +275,7 @@ const SimpleKeywords SimpleParser6::SUBNET6_PARAMETERS = {
     { "ddns-ttl",                       Element::integer },
     { "ddns-ttl-min",                   Element::integer },
     { "ddns-ttl-max",                   Element::integer },
+    { "adaptive-lease-time-threshold",  Element::real },
 };
 
 /// @brief This table defines default values for each IPv6 subnet.
@@ -329,7 +331,8 @@ const ParamsList SimpleParser6::INHERIT_TO_SUBNET6 = {
     "cache-threshold",
     "cache-max-age",
     "allocator",
-    "pd-allocator"
+    "pd-allocator",
+    "adaptive-lease-time-threshold",
 };
 
 /// @brief This table defines all pool parameters.
@@ -439,6 +442,7 @@ const SimpleKeywords SimpleParser6::SHARED_NETWORK6_PARAMETERS = {
     { "ddns-ttl",                       Element::integer },
     { "ddns-ttl-min",                   Element::integer },
     { "ddns-ttl-max",                   Element::integer },
+    { "adaptive-lease-time-threshold",  Element::real },
 };
 
 /// @brief This table defines default values for interfaces for DHCPv6.

src/lib/dhcpsrv/tests/alloc_engine4_unittest.cc

@@ -5002,6 +5002,209 @@ TEST_F(AllocEngine4Test, getTemplateClassValidLft4) {
     }
 }
 
+// Verifies that AllocEngine::getMinValidLft(ctx4, valid) sets the appropriate
+// lifetime value based on the context content.
+TEST_F(AllocEngine4Test, getMinValidLft4) {
+    AllocEngine engine(0);
+
+    // Let's make three classes, two with valid-lifetime and one without,
+    // and add them to the dictionary.
+    ClientClassDictionaryPtr dictionary = CfgMgr::instance().getStagingCfg()->getClientClassDictionary();
+    ExpressionPtr match_expr;
+    ExpressionParser parser;
+
+    ElementPtr test_cfg = Element::create("'valid_one_value'");
+    parser.parse(match_expr, test_cfg, AF_INET, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    ClientClassDefPtr class_def(new TemplateClientClassDef("valid_one", match_expr));
+    Triplet<uint32_t> valid_one(50, 100, 150);
+    class_def->setValid(valid_one);
+    dictionary->addClass(class_def);
+
+    test_cfg = Element::create("'valid_two_value'");
+    parser.parse(match_expr, test_cfg, AF_INET, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    class_def.reset(new TemplateClientClassDef("valid_two", match_expr));
+    Triplet<uint32_t>valid_two(200, 250, 300);
+    class_def->setValid(valid_two);
+    dictionary->addClass(class_def);
+
+    test_cfg = Element::create("'valid_unspec_value'");
+    parser.parse(match_expr, test_cfg, AF_INET, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    class_def.reset(new TemplateClientClassDef("valid_unspec", match_expr));
+    dictionary->addClass(class_def);
+
+    // Commit our class changes.
+    CfgMgr::instance().commit();
+
+    // Update the subnet's triplet to something more useful.
+    subnet_->setValid(Triplet<uint32_t>(500, 1000, 1500));
+
+    // Describes a test scenario.
+    struct Scenario {
+        std::string desc_;                  // descriptive text for logging
+        std::vector<std::string> classes_;  // class list of assigned classes
+        uint32_t requested_lft_;            // use as option 51 is > 0
+        uint32_t remaining_lft_;            // remaining lifime or 0
+        uint32_t exp_valid_;                // expected lifetime
+    };
+
+    // Scenarios to test.
+    std::vector<Scenario> scenarios = {
+        {
+            "BOOTP",
+            { "BOOTP" },
+            0,
+            0,
+            Lease::INFINITY_LFT
+        },
+        {
+            "no classes, no option, remain 0",
+            {},
+            0,
+            0,
+            subnet_->getValid().getMin()
+        },
+        {
+            "no classes, no option, remain too small",
+            {},
+            0,
+            100,
+            subnet_->getValid().getMin()
+        },
+        {
+            "no classes, no option, remain",
+            {},
+            0,
+            800,
+            800
+        },
+        {
+            "no classes, option, remain 0",
+            {},
+            1000,
+            0,
+            subnet_->getValid().getMin()
+        },
+        {
+            "class unspecified, no option, remain 0",
+            { "valid_unspec" },
+            0,
+            0,
+            subnet_->getValid().getMin()
+        },
+        {
+            "from last class, no option, remain 0",
+            { "valid_unspec", "valid_one" },
+            0,
+            0,
+            valid_one.getMin()
+        },
+        {
+            "from first class, no option, remain 0",
+            { "valid_two", "valid_one" },
+            0,
+            0,
+            valid_two.getMin()
+        },
+        {
+            "class plus remain too small",
+            { "valid_one" },
+            0,
+            10,
+            valid_one.getMin(),
+        },
+        {
+            "class plus remain",
+            { "valid_one" },
+            0,
+            100,
+            100
+        }
+    };
+
+    // Iterate over the scenarios and verify the correct outcome.
+    for (auto const& scenario : scenarios) {
+        SCOPED_TRACE(scenario.desc_); {
+            // Create a context;
+            AllocEngine::ClientContext4 ctx(subnet_, ClientIdPtr(), hwaddr_,
+                                            IOAddress("0.0.0.0"), false, false,
+                                            "", false);
+            ctx.query_.reset(new Pkt4(DHCPDISCOVER, 1234));
+
+            // Add client classes (if any)
+            for (auto const& class_name : scenario.classes_) {
+                if (class_name == "BOOTP") {
+                    ctx.query_->addClass(class_name);
+                } else {
+                    string subclass(TemplateClientClassDef::SPAWN_CLASS_PREFIX);
+                    subclass += class_name;
+                    subclass += "_value";
+                    ctx.query_->addSubClass(class_name, subclass);
+                }
+            }
+
+            // Add client option (if one)
+            if (scenario.requested_lft_) {
+                OptionUint32Ptr opt(new OptionUint32(Option::V4, DHO_DHCP_LEASE_TIME,
+                                                     scenario.requested_lft_));
+                ctx.query_->addOption(opt);
+            }
+
+            uint32_t valid = scenario.remaining_lft_;
+            engine.getMinValidLft(ctx, valid);
+            EXPECT_EQ(valid, scenario.exp_valid_);
+        }
+    }
+}
+
+// Verifies that AllocEngine::getRemaining retuns the remaining lifetime value.
+TEST_F(AllocEngine4Test, getRemaining) {
+    // No Lease.
+    uint32_t valid(1);
+    Lease4Ptr lease;
+    AllocEngine::getRemaining(lease, valid);
+    EXPECT_EQ(0, valid);
+
+    // Unexpected state.
+    valid = 1;
+    uint8_t hwaddr_data[] = { 0, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe };
+    HWAddrPtr hwaddr(new HWAddr(hwaddr_data, sizeof(hwaddr_data), HTYPE_ETHER));
+    uint8_t clientid[] = { 8, 7, 6, 5, 4, 3, 2, 1 };
+    time_t now = time(0);
+    lease.reset(new Lease4(IOAddress("192.0.2.100"), hwaddr, clientid,
+                           sizeof(clientid), 100, now, 1));
+    lease->state_ = Lease::STATE_DECLINED;
+    AllocEngine::getRemaining(lease, valid);
+    EXPECT_EQ(0, valid);
+
+    // Infinite lifetime.
+    lease->state_ = Lease::STATE_DEFAULT;
+    uint32_t infinity_lft = Lease::INFINITY_LFT;
+    lease->valid_lft_ = lease->current_valid_lft_ = infinity_lft;
+    AllocEngine::getRemaining(lease, valid);
+    EXPECT_EQ(infinity_lft, valid);
+
+    // Time going backward.
+    lease->cltt_ = lease->current_cltt_ = now + 100;
+    lease->valid_lft_ = lease->current_valid_lft_ = 50;
+    AllocEngine::getRemaining(lease, valid);
+    EXPECT_EQ(0, valid);
+
+    // Already expired.
+    valid = 1;
+    lease->cltt_ = lease->current_cltt_ = now - 100;
+    AllocEngine::getRemaining(lease, valid);
+    EXPECT_EQ(0, valid);
+
+    // Valid case.
+    now = time(0);
+    lease->cltt_ = lease->current_cltt_ = now - 10;
+    AllocEngine::getRemaining(lease, valid);
+    EXPECT_NEAR(40, valid, 1);
+}
+
 // This test checks that deleteRelease handles BOOTP leases.
 TEST_F(AllocEngine4Test, bootpDelete) {
     boost::scoped_ptr<AllocEngine> engine;

src/lib/dhcpsrv/tests/alloc_engine6_unittest.cc

@@ -6324,6 +6324,358 @@ TEST_F(AllocEngine6Test, getTemplateClassPreferredLifetime) {
     }
 }
 
+// Verifies that AllocEngine::getMinLifetimes6() returns the appropriate
+// valid lifetime value based on the context content.
+TEST_F(AllocEngine6Test, getMinValidLifetime) {
+    boost::scoped_ptr<AllocEngine> engine;
+    ASSERT_NO_THROW(engine.reset(new AllocEngine(100)));
+    ASSERT_TRUE(engine);
+
+    // Let's make three classes, two with valid-lifetime and one without,
+    // and add them to the dictionary.
+    ClientClassDictionaryPtr dictionary = CfgMgr::instance().getStagingCfg()->getClientClassDictionary();
+    ExpressionPtr match_expr;
+    ExpressionParser parser;
+
+    ElementPtr test_cfg = Element::create("'valid_one_value'");
+    parser.parse(match_expr, test_cfg, AF_INET6, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    ClientClassDefPtr class_def(new TemplateClientClassDef("valid_one", match_expr));
+    Triplet<uint32_t> valid_one(50, 100, 150);
+    class_def->setValid(valid_one);
+    dictionary->addClass(class_def);
+
+    test_cfg = Element::create("'valid_two_value'");
+    parser.parse(match_expr, test_cfg, AF_INET6, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    class_def.reset(new TemplateClientClassDef("valid_two", match_expr));
+    Triplet<uint32_t>valid_two(200, 250, 300);
+    class_def->setValid(valid_two);
+    dictionary->addClass(class_def);
+
+    test_cfg = Element::create("'valid_unspec_value'");
+    parser.parse(match_expr, test_cfg, AF_INET6, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    class_def.reset(new TemplateClientClassDef("valid_unspec", match_expr));
+    dictionary->addClass(class_def);
+
+    // Commit our class changes.
+    CfgMgr::instance().commit();
+
+    // Update the subnet's triplet to something more useful.
+    subnet_->setValid(Triplet<uint32_t>(500, 1000, 1500));
+
+    // Describes a test scenario.
+    struct Scenario {
+        std::string desc_;                  // descriptive text for logging
+        std::vector<std::string> classes_;  // class list of assigned classes
+        uint32_t requested_lft_;            // use as option 51 is > 0
+        uint32_t remaining_lft_;            // remaining valid lifetime
+        uint32_t exp_valid_;                // expected lifetime
+    };
+
+    // Scenarios to test.
+    std::vector<Scenario> scenarios = {
+        {
+            "no classes, no hint, remain 0",
+            {},
+            0,
+            0,
+            subnet_->getValid().getMin()
+        },
+        {
+            "no classes, no hint, remain too small",
+            {},
+            0,
+            100,
+            subnet_->getValid().getMin()
+        },
+        {
+            "no classes, no hint, remain",
+            {},
+            0,
+            800,
+            800
+        },
+        {
+            "no classes, hint, remain 0",
+            {},
+            800,
+            0,
+            subnet_->getValid().getMin()
+        },
+        {
+            "class unspecified, no hint, remain 0",
+            { "valid_unspec" },
+            0,
+            0,
+            subnet_->getValid().getMin()
+        },
+        {
+            "from last class, no hint, remain 0",
+            { "valid_unspec", "valid_one" },
+            0,
+            0,
+            valid_one.getMin()
+        },
+        {
+            "from first class, no hint, remain 0",
+            { "valid_two", "valid_one" },
+            0,
+            0,
+            valid_two.getMin()
+        },
+        {
+            "class plus remain too small",
+            { "valid_one" },
+            0,
+            10,
+            valid_one.getMin()
+        },
+        {
+            "class plus remain",
+            { "valid_one" },
+            0,
+            100,
+            100
+        }
+    };
+
+    // Iterate over the scenarios and verify the correct outcome.
+    for (auto const& scenario : scenarios) {
+        SCOPED_TRACE(scenario.desc_); {
+            // Create a context;
+            AllocEngine::ClientContext6 ctx(subnet_, duid_, false, false, "", true,
+                                            Pkt6Ptr(new Pkt6(DHCPV6_SOLICIT, 1234)));
+            // Add client classes (if any)
+            for (auto const& class_name : scenario.classes_) {
+                ctx.query_->addClass(class_name);
+            }
+
+            // Add hint
+            ctx.currentIA().iaid_ = iaid_;
+
+            // prefix, prefixlen, preferred, valid
+            ctx.currentIA().addHint(IOAddress("::"), 128, 0, scenario.requested_lft_);
+            uint32_t valid = scenario.remaining_lft_;
+            uint32_t preferred = 0;
+
+            engine->getMinLifetimes6(ctx, preferred, valid);
+            EXPECT_EQ(valid, scenario.exp_valid_);
+        }
+    }
+}
+
+// Verifies that AllocEngine::getMinLifetimes6() returns the appropriate
+// preferred lifetime value based on the context content.
+TEST_F(AllocEngine6Test, getMinPreferredLifetime) {
+    boost::scoped_ptr<AllocEngine> engine;
+    ASSERT_NO_THROW(engine.reset(new AllocEngine(100)));
+    ASSERT_TRUE(engine);
+
+    // Let's make three classes, two with preferred-lifetime and one without,
+    // and add them to the dictionary.
+    ClientClassDictionaryPtr dictionary = CfgMgr::instance().getStagingCfg()->getClientClassDictionary();
+    ExpressionPtr match_expr;
+    ExpressionParser parser;
+
+    ElementPtr test_cfg = Element::create("'preferred_one_value'");
+    parser.parse(match_expr, test_cfg, AF_INET6, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    ClientClassDefPtr class_def(new TemplateClientClassDef("preferred_one", match_expr));
+    Triplet<uint32_t> preferred_one(50, 100, 150);
+    class_def->setPreferred(preferred_one);
+    dictionary->addClass(class_def);
+
+    test_cfg = Element::create("'preferred_two_value'");
+    parser.parse(match_expr, test_cfg, AF_INET6, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    class_def.reset(new TemplateClientClassDef("preferred_two", match_expr));
+    Triplet<uint32_t>preferred_two(200, 250, 300);
+    class_def->setPreferred(preferred_two);
+    dictionary->addClass(class_def);
+
+    test_cfg = Element::create("'preferred_unspec_value'");
+    parser.parse(match_expr, test_cfg, AF_INET6, EvalContext::acceptAll, EvalContext::PARSER_STRING);
+
+    class_def.reset(new TemplateClientClassDef("preferred_unspec", match_expr));
+    dictionary->addClass(class_def);
+
+    // Commit our class changes.
+    CfgMgr::instance().commit();
+
+    // Update the subnet's triplet to something more useful. Note that
+    // valid is 400 for the subnet.
+    subnet_->setPreferred(Triplet<uint32_t>(300, 350, 450));
+
+    // Describes a test scenario.
+    struct Scenario {
+        std::string desc_;                  // descriptive text for logging
+        std::vector<std::string> classes_;  // class list of assigned classes
+        uint32_t requested_lft_;            // use as option 51 is > 0
+        uint32_t remaining_lft_;            // remaining preferred lifetime
+        uint32_t exp_preferred_;            // expected lifetime
+    };
+
+    // Scenarios to test.
+    std::vector<Scenario> scenarios = {
+        {
+            "no classes, no hint, remain 0",
+            {},
+            0,
+            0,
+            subnet_->getPreferred().getMin()
+        },
+        {
+            "no classes, no hint, remain too small",
+            {},
+            0,
+            100,
+            subnet_->getPreferred().getMin()
+        },
+        {
+            "no classes, no hint, remain",
+            {},
+            0,
+            350,
+            350
+        },
+        {
+            "no classes, no hint, remain too big",
+            {},
+            0,
+            500,
+            subnet_->getValid().getMin() * 5 / 8
+        },
+        {
+            "no classes, hint, remain 0",
+            {},
+            800,
+            0,
+            subnet_->getPreferred().getMin()
+        },
+        {
+            "class unspecified, no hint, remain 0",
+            { "preferred_unspec" },
+            0,
+            0,
+            subnet_->getPreferred().getMin()
+        },
+        {
+            "from last class, no hint, remain 0",
+            { "preferred_unspec", "preferred_one" },
+            0,
+            0,
+            preferred_one.getMin()
+        },
+        {
+            "from first class, no hint, remain 0",
+            { "preferred_two", "preferred_one" },
+            0,
+            0,
+            preferred_two.getMin()
+        },
+        {
+            "class plus remain too small",
+            { "preferred_one" },
+            0,
+            10,
+            preferred_one.getMin()
+        },
+        {
+            "class plus remain",
+            { "preferred_one" },
+            0,
+            100,
+            100
+        }
+    };
+
+    // Iterate over the scenarios and verify the correct outcome.
+    for (auto const& scenario : scenarios) {
+        SCOPED_TRACE(scenario.desc_); {
+            // Create a context;
+            AllocEngine::ClientContext6 ctx(subnet_, duid_, false, false, "", true,
+                                            Pkt6Ptr(new Pkt6(DHCPV6_SOLICIT, 1234)));
+            // Add client classes (if any)
+            for (auto const& class_name : scenario.classes_) {
+                string subclass(TemplateClientClassDef::SPAWN_CLASS_PREFIX);
+                subclass += class_name;
+                subclass += "_value";
+                ctx.query_->addSubClass(class_name, subclass);
+            }
+
+            // Add hint
+            ctx.currentIA().iaid_ = iaid_;
+
+            // prefix, prefixlen, preferred, valid
+            ctx.currentIA().addHint(IOAddress("::"), 128, scenario.requested_lft_, 0);
+
+            uint32_t valid = 0;
+            uint32_t preferred = scenario.remaining_lft_;
+
+            engine->getMinLifetimes6(ctx, preferred, valid);
+            EXPECT_EQ(preferred, scenario.exp_preferred_);
+        }
+    }
+}
+
+// Verifies that AllocEngine::getRemaining retuns the remaining lifetime values.
+TEST_F(AllocEngine6Test, getRemaining) {
+    // No Lease.
+    uint32_t valid(1);
+    uint32_t preferred(1);
+    Lease6Ptr lease;
+    AllocEngine::getRemaining(lease, preferred, valid);
+    EXPECT_EQ(0, valid);
+    EXPECT_EQ(0, preferred);
+
+    // Unexpected state.
+    valid = 1;
+    preferred = 1;
+    DuidPtr duid(new DUID(vector<uint8_t>(12, 0xff)));
+    const uint32_t  iaid = 3568;
+    time_t now = time(0);
+    lease.reset(new Lease6(Lease::TYPE_NA, IOAddress("2001:db8:1::1"), duid,
+                           iaid, 30, 50, 1));
+    lease->state_ = Lease::STATE_DECLINED;
+    AllocEngine::getRemaining(lease, preferred, valid);
+    EXPECT_EQ(0, valid);
+    EXPECT_EQ(0, preferred);
+
+    // Time going backward.
+    valid = 1;
+    preferred = 1;
+    lease->state_ = Lease::STATE_DEFAULT;
+    lease->cltt_ = lease->current_cltt_ = now + 100;
+    lease->valid_lft_ = lease->current_valid_lft_ = 50;
+    AllocEngine::getRemaining(lease, preferred, valid);
+    EXPECT_EQ(0, valid);
+    EXPECT_EQ(0, preferred);
+
+    // Already expired.
+    valid = 1;
+    preferred = 1;
+    lease->cltt_ = lease->current_cltt_ = now - 100;
+    AllocEngine::getRemaining(lease, preferred, valid);
+    EXPECT_EQ(0, valid);
+    EXPECT_EQ(0, preferred);
+
+    // Valid case.
+    now = time(0);
+    lease->cltt_ = lease->current_cltt_ = now - 10;
+    AllocEngine::getRemaining(lease, preferred, valid);
+    EXPECT_NEAR(40, valid, 1);
+    EXPECT_NEAR(20, preferred, 1);
+
+    // No longer preferred.
+    now = time(0);
+    lease->cltt_ = lease->current_cltt_ = now - 40;
+    AllocEngine::getRemaining(lease, preferred, valid);
+    EXPECT_NEAR(10, valid, 1);
+    EXPECT_EQ(0, preferred);
+}
+
 }  // namespace test
 }  // namespace dhcp
 }  // namespace isc

src/lib/dhcpsrv/tests/cfg_shared_networks4_unittest.cc

@@ -210,6 +210,7 @@ TEST(CfgSharedNetworks4Test, unparse) {
     network1->setHostnameCharReplacement("x");
     network1->setCacheThreshold(.20);
     network1->setOfferLft(77);
+    network1->setAdaptiveLeaseTimeThreshold(.90);
 
     network2->setIface("eth1");
     network2->setT1(Triplet<uint32_t>(100));
@@ -255,6 +256,7 @@ TEST(CfgSharedNetworks4Test, unparse) {
         "    \"cache-max-age\": 50\n"
         "  },\n"
         "  {\n"
+        "    \"adaptive-lease-time-threshold\": .90,\n"
         "    \"calculate-tee-times\": true,\n"
         "    \"ddns-generated-prefix\": \"prefix\",\n"
         "    \"ddns-override-no-update\": true,\n"

src/lib/dhcpsrv/tests/cfg_subnets4_unittest.cc

@@ -1087,6 +1087,7 @@ TEST(CfgSubnets4Test, unparseSubnet) {
     subnet1->setT1Percent(0.45);
     subnet1->setT2Percent(0.70);
     subnet1->setCacheThreshold(0.20);
+    subnet1->setAdaptiveLeaseTimeThreshold(.90);
 
     subnet2->setIface("lo");
     subnet2->addRelayAddress(IOAddress("10.0.0.1"));
@@ -1146,6 +1147,7 @@ TEST(CfgSubnets4Test, unparseSubnet) {
         "    \"4o6-interface\": \"\",\n"
         "    \"4o6-interface-id\": \"\",\n"
         "    \"4o6-subnet\": \"\",\n"
+        "    \"adaptive-lease-time-threshold\": .90,\n"
         "    \"option-data\": [ ],\n"
         "    \"pools\": [ ],\n"
         "    \"user-context\": { \"comment\": \"foo\" }\n"
@@ -1821,6 +1823,10 @@ TEST(CfgSubnets4Test, cacheParamValidation) {
         {"too big", 1.05,
          "subnet configuration failed: cache-threshold:"
          " 1.05 is invalid, it must be greater than or equal to 0.0 and less than 1.0"
+        },
+        {"excluded", 1.0,
+         "subnet configuration failed: cache-threshold:"
+         " 1 is invalid, it must be greater than or equal to 0.0 and less than 1.0"
         }
     };
 
@@ -1849,7 +1855,6 @@ TEST(CfgSubnets4Test, cacheParamValidation) {
         "            \"4o6-subnet\": \"\" \n"
         "        }";
 
-
     data::ElementPtr elems;
     ASSERT_NO_THROW(elems = data::Element::fromJSON(json))
                     << "invalid JSON:" << json << "\n test is broken";
@@ -1887,6 +1892,99 @@ TEST(CfgSubnets4Test, cacheParamValidation) {
     }
 }
 
+// This test verifies the Subnet4 parser's validation logic for
+// adaptive lease time parameter.
+TEST(CfgSubnets4Test, adaptiveLeaseTimeParamValidation) {
+
+    // Describes a single test scenario.
+    struct Scenario {
+        std::string label;         // label used for logging test failures
+        double threshold;          // value of adaptive-lease-time-threshold
+        std::string error_message; // expected error message is parsing should fail
+    };
+
+    // Test Scenarios.
+    std::vector<Scenario> tests = {
+        {"valid", .25, ""},
+        {"valid", 1.0, ""},
+        {"negative", -.25,
+         "subnet configuration failed: adaptive-lease-time-threshold:"
+         " -0.25 is invalid, it must be greater than 0.0 and less than or equal to 1.0"
+        },
+        {"excluded", 0.,
+         "subnet configuration failed: adaptive-lease-time-threshold:"
+         " 0 is invalid, it must be greater than 0.0 and less than or equal to 1.0"
+        },
+        {"too big", 1.05,
+         "subnet configuration failed: adaptive-lease-time-threshold:"
+         " 1.05 is invalid, it must be greater than 0.0 and less than or equal to 1.0"
+        }
+    };
+
+    // First we create a set of elements that provides all
+    // required for a Subnet4.
+    std::string json =
+        "        {"
+        "            \"id\": 1,\n"
+        "            \"subnet\": \"10.1.2.0/24\", \n"
+        "            \"interface\": \"\", \n"
+        "            \"renew-timer\": 100, \n"
+        "            \"rebind-timer\": 200, \n"
+        "            \"valid-lifetime\": 300, \n"
+        "            \"match-client-id\": false, \n"
+        "            \"authoritative\": false, \n"
+        "            \"next-server\": \"\", \n"
+        "            \"server-hostname\": \"\", \n"
+        "            \"boot-file-name\": \"\", \n"
+        "            \"client-classes\": [], \n"
+        "            \"evaluate-additional-classes\": [], \n"
+        "            \"reservations-global\": false, \n"
+        "            \"reservations-in-subnet\": true, \n"
+        "            \"reservations-out-of-pool\": false, \n"
+        "            \"4o6-interface\": \"\", \n"
+        "            \"4o6-interface-id\": \"\", \n"
+        "            \"4o6-subnet\": \"\" \n"
+        "        }";
+
+    data::ElementPtr elems;
+    ASSERT_NO_THROW(elems = data::Element::fromJSON(json))
+                    << "invalid JSON:" << json << "\n test is broken";
+
+    // Iterate over the test scenarios, verifying each prescribed
+    // outcome.
+    for (auto const& test : tests) {
+        {
+            SCOPED_TRACE("test: " + test.label);
+
+            // Set this scenario's configuration parameters
+            elems->set("adaptive-lease-time-threshold",
+                       data::Element::create(test.threshold));
+
+            Subnet4Ptr subnet;
+            try {
+                // Attempt to parse the configuration.
+                Subnet4ConfigParser parser;
+                subnet = parser.parse(elems);
+            } catch (const std::exception& ex) {
+                if (!test.error_message.empty()) {
+                    // We expected a failure, did we fail the correct way?
+                    EXPECT_EQ(test.error_message, ex.what());
+                } else {
+                    // Should not have failed.
+                    ADD_FAILURE() << "Scenario should not have failed: " << ex.what();
+                }
+
+                // Either way we're done with this scenario.
+                continue;
+            }
+
+            // We parsed correctly, make sure the values are right.
+            EXPECT_TRUE(util::areDoublesEquivalent(test.threshold,
+                                                   subnet->getAdaptiveLeaseTimeThreshold()));
+        }
+    }
+}
+
 // This test verifies that the optional interface check works as expected.
 TEST(CfgSubnets4Test, iface) {
     // Create a configuration.

src/lib/dhcpsrv/tests/cfg_subnets6_unittest.cc

@@ -684,6 +684,7 @@ TEST(CfgSubnets6Test, unparseSubnet) {
     subnet1->setT1Percent(0.45);
     subnet1->setT2Percent(0.70);
     subnet1->setCacheThreshold(0.20);
+    subnet1->setAdaptiveLeaseTimeThreshold(.90);
 
     subnet2->setIface("lo");
     subnet2->addRelayAddress(IOAddress("2001:db8:ff::2"));
@@ -740,6 +741,7 @@ TEST(CfgSubnets6Test, unparseSubnet) {
         "    \"valid-lifetime\": 4,\n"
         "    \"min-valid-lifetime\": 4,\n"
         "    \"max-valid-lifetime\": 4,\n"
+        "    \"adaptive-lease-time-threshold\": .90,\n"
         "    \"client-classes\": [ \"foo\", \"bar\" ],\n"
         "    \"pools\": [ ],\n"
         "    \"pd-pools\": [ ],\n"
@@ -1610,6 +1612,10 @@ TEST(CfgSubnets6Test, cacheParamValidation) {
         {"too big", 1.05,
          "subnet configuration failed: cache-threshold:"
          " 1.05 is invalid, it must be greater than or equal to 0.0 and less than 1.0"
+        },
+        {"excluded", 1.0,
+         "subnet configuration failed: cache-threshold:"
+         " 1 is invalid, it must be greater than or equal to 0.0 and less than 1.0"
         }
     };
 
@@ -1667,6 +1673,91 @@ TEST(CfgSubnets6Test, cacheParamValidation) {
     }
 }
 
+// This test verifies the Subnet6 parser's validation logic for
+// adaptive lease time parameter.
+TEST(CfgSubnets6Test, adaptiveLeaseTimeParamValidation) {
+
+    // Describes a single test scenario.
+    struct Scenario {
+        std::string label;         // label used for logging test failures
+        double threshold;          // value of adaptive-lease-time-threshold
+        std::string error_message; // expected error message is parsing should fail
+    };
+
+    // Test Scenarios.
+    std::vector<Scenario> tests = {
+        {"valid", .25, ""},
+        {"valid", 1.0, ""},
+        {"negative", -.25,
+         "subnet configuration failed: adaptive-lease-time-threshold:"
+         " -0.25 is invalid, it must be greater than 0.0 and less than or equal to 1.0"
+        },
+        {"excluded", 0.,
+         "subnet configuration failed: adaptive-lease-time-threshold:"
+         " 0 is invalid, it must be greater than 0.0 and less than or equal to 1.0"
+        },
+        {"too big", 1.05,
+         "subnet configuration failed: adaptive-lease-time-threshold:"
+         " 1.05 is invalid, it must be greater than 0.0 and less than or equal to 1.0"
+        }
+    };
+
+    // First we create a set of elements that provides all
+    // required for a Subnet6.
+    std::string json =
+        "        {"
+        "            \"id\": 1,\n"
+        "            \"subnet\": \"2001:db8:1::/64\", \n"
+        "            \"interface\": \"\", \n"
+        "            \"renew-timer\": 100, \n"
+        "            \"rebind-timer\": 200, \n"
+        "            \"valid-lifetime\": 300, \n"
+        "            \"client-classes\": [], \n"
+        "            \"evaluate-additional-classes\": [], \n"
+        "            \"reservations-global\": false, \n"
+        "            \"reservations-in-subnet\": true, \n"
+        "            \"reservations-out-of-pool\": false \n"
+        "        }";
+
+    data::ElementPtr elems;
+    ASSERT_NO_THROW(elems = data::Element::fromJSON(json))
+                    << "invalid JSON:" << json << "\n test is broken";
+
+    // Iterate over the test scenarios, verifying each prescribed
+    // outcome.
+    for (auto const& test : tests) {
+        {
+            SCOPED_TRACE("test: " + test.label);
+
+            // Set this scenario's configuration parameters
+            elems->set("adaptive-lease-time-threshold",
+                       data::Element::create(test.threshold));
+
+            Subnet6Ptr subnet;
+            try {
+                // Attempt to parse the configuration.
+                Subnet6ConfigParser parser;
+                subnet = parser.parse(elems);
+            } catch (const std::exception& ex) {
+                if (!test.error_message.empty()) {
+                    // We expected a failure, did we fail the correct way?
+                    EXPECT_EQ(test.error_message, ex.what());
+                } else {
+                    // Should not have failed.
+                    ADD_FAILURE() << "Scenario should not have failed: " << ex.what();
+                }
+
+                // Either way we're done with this scenario.
+                continue;
+            }
+
+            // We parsed correctly, make sure the values are right.
+            EXPECT_TRUE(util::areDoublesEquivalent(test.threshold,
+                                                   subnet->getAdaptiveLeaseTimeThreshold()));
+        }
+    }
+}
+
 // This test verifies that the optional interface check works as expected.
 TEST(CfgSubnets6Test, iface) {
     // Create a configuration.

src/lib/dhcpsrv/tests/dhcp_parsers_unittest.cc

@@ -78,157 +78,157 @@ public:
     // Verifies valid permutations of ddns-ttl-percent, ddns-ttl,
     // ddns-ttl-min, and ddns-ttl-max values for SubnetX.
     template<typename ParserType, typename NetworkPtrType>
-	void validDdnsTtlParmatersSubnet(int family) {
-	    struct Scenario {
-	        size_t line_no_;
-	        std::string json_;
-	        double ddns_ttl_percent_;
-	        uint32_t ddns_ttl_;
-	        uint32_t ddns_ttl_min_;
-	        uint32_t ddns_ttl_max_;
-	    };
+        void validDdnsTtlParmatersSubnet(int family) {
+            struct Scenario {
+                size_t line_no_;
+                std::string json_;
+                double ddns_ttl_percent_;
+                uint32_t ddns_ttl_;
+                uint32_t ddns_ttl_min_;
+                uint32_t ddns_ttl_max_;
+            };
 
-	    std::list<Scenario> scenarios = {
-	    {
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl": 100
-	        })^",
-	        0.0, 100, 0, 0
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl-percent": 5.0
-	        })^",
-	        5.0, 0, 0, 0
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl-min": 25
-	        })^",
-	        0.0, 0, 25, 0
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl-max": 150
-	        })^",
-	        0.0, 0, 0, 150
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl-min": 25,
-	            "ddns-ttl-max": 150
-	        })^",
-	        0.0, 0, 25, 150
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1, "subnet": "192.0.2.0/24",
-	            "ddns-ttl-percent": 5.0,
-	            "ddns-ttl-min": 25,
-	            "ddns-ttl-max": 150
-	        })^",
-	        5.0, 0, 25, 150
-	    }};
+            std::list<Scenario> scenarios = {
+            {
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl": 100
+                })^",
+                0.0, 100, 0, 0
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl-percent": 5.0
+                })^",
+                5.0, 0, 0, 0
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl-min": 25
+                })^",
+                0.0, 0, 25, 0
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl-max": 150
+                })^",
+                0.0, 0, 0, 150
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl-min": 25,
+                    "ddns-ttl-max": 150
+                })^",
+                0.0, 0, 25, 150
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1, "subnet": "192.0.2.0/24",
+                    "ddns-ttl-percent": 5.0,
+                    "ddns-ttl-min": 25,
+                    "ddns-ttl-max": 150
+                })^",
+                5.0, 0, 25, 150
+            }};
 
         ElementPtr subnet_elem = Element::create(family == AF_INET ?
                                                  "192.0.2.0/24" : "2001:db8::/64");
-	    for (const auto& scenario : scenarios) {
-	        std::stringstream oss;
-	        oss << "scenario at " << scenario.line_no_;
-	        SCOPED_TRACE(oss.str());
+            for (const auto& scenario : scenarios) {
+                std::stringstream oss;
+                oss << "scenario at " << scenario.line_no_;
+                SCOPED_TRACE(oss.str());
 
-	        // Parse configuration specified above.
-	        ElementPtr config_element;
-	        ASSERT_NO_THROW_LOG(config_element = Element::fromJSON(scenario.json_));
+                // Parse configuration specified above.
+                ElementPtr config_element;
+                ASSERT_NO_THROW_LOG(config_element = Element::fromJSON(scenario.json_));
             config_element->set("subnet", subnet_elem);
 
-	        ParserType parser(family);
+                ParserType parser(family);
 
-	        NetworkPtrType subnet;
+                NetworkPtrType subnet;
 
-	        ASSERT_NO_THROW_LOG(subnet = parser.parse(config_element));
-	        ASSERT_TRUE(subnet);
+                ASSERT_NO_THROW_LOG(subnet = parser.parse(config_element));
+                ASSERT_TRUE(subnet);
 
-	        EXPECT_EQ(subnet->getDdnsTtlPercent().unspecified(), (scenario.ddns_ttl_percent_ == 0.0));
-	        EXPECT_EQ(subnet->getDdnsTtlPercent(), scenario.ddns_ttl_percent_);
+                EXPECT_EQ(subnet->getDdnsTtlPercent().unspecified(), (scenario.ddns_ttl_percent_ == 0.0));
+                EXPECT_EQ(subnet->getDdnsTtlPercent(), scenario.ddns_ttl_percent_);
 
-	        EXPECT_EQ(subnet->getDdnsTtl().unspecified(), (scenario.ddns_ttl_ == 0));
-	        EXPECT_EQ(subnet->getDdnsTtl(), scenario.ddns_ttl_);
+                EXPECT_EQ(subnet->getDdnsTtl().unspecified(), (scenario.ddns_ttl_ == 0));
+                EXPECT_EQ(subnet->getDdnsTtl(), scenario.ddns_ttl_);
 
-	        EXPECT_EQ(subnet->getDdnsTtlMin().unspecified(), (scenario.ddns_ttl_min_ == 0));
-	        EXPECT_EQ(subnet->getDdnsTtlMin(), scenario.ddns_ttl_min_);
+                EXPECT_EQ(subnet->getDdnsTtlMin().unspecified(), (scenario.ddns_ttl_min_ == 0));
+                EXPECT_EQ(subnet->getDdnsTtlMin(), scenario.ddns_ttl_min_);
 
-	        EXPECT_EQ(subnet->getDdnsTtlMax().unspecified(), (scenario.ddns_ttl_max_ == 0));
-	        EXPECT_EQ(subnet->getDdnsTtlMax(), scenario.ddns_ttl_max_);
-	    }
-	}
+                EXPECT_EQ(subnet->getDdnsTtlMax().unspecified(), (scenario.ddns_ttl_max_ == 0));
+                EXPECT_EQ(subnet->getDdnsTtlMax(), scenario.ddns_ttl_max_);
+            }
+        }
 
-	// Verifies invalid permutations of ddns-ttl-percent, ddns-ttl,
-	// ddns-ttl-min, and ddns-ttl-max values for SubnetX.
+        // Verifies invalid permutations of ddns-ttl-percent, ddns-ttl,
+        // ddns-ttl-min, and ddns-ttl-max values for SubnetX.
     template<typename ParserType>
-	void invalidDdnsTtlParmatersSubnet(int family) {
-	    struct Scenario {
-	        size_t line_no_;
-	        std::string json_;
-	        std::string exp_message_;
-	    };
+        void invalidDdnsTtlParmatersSubnet(int family) {
+            struct Scenario {
+                size_t line_no_;
+                std::string json_;
+                std::string exp_message_;
+            };
 
-	    std::list<Scenario> scenarios = {
-	    {
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl-percent": 5.0,
-	            "ddns-ttl": 100
-	        })^",
-	        "subnet configuration failed: cannot specify both ddns-ttl-percent and ddns-ttl"
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl": 100,
-	            "ddns-ttl-min": 25
-	        })^",
-	        "subnet configuration failed: cannot specify both ddns-ttl-min and ddns-ttl"
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl": 100,
-	            "ddns-ttl-max": 150
-	        })^",
-	        "subnet configuration failed: cannot specify both ddns-ttl-max and ddns-ttl"
-	    },{
-	        __LINE__,
-	        R"^({
-	            "id": 1,
-	            "ddns-ttl-min": 150,
-	            "ddns-ttl-max": 25
-	        })^",
-	        "subnet configuration failed: ddns-ttl-max: 25 must be greater than ddns-ttl-min: 150"
-	    }};
+            std::list<Scenario> scenarios = {
+            {
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl-percent": 5.0,
+                    "ddns-ttl": 100
+                })^",
+                "subnet configuration failed: cannot specify both ddns-ttl-percent and ddns-ttl"
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl": 100,
+                    "ddns-ttl-min": 25
+                })^",
+                "subnet configuration failed: cannot specify both ddns-ttl-min and ddns-ttl"
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl": 100,
+                    "ddns-ttl-max": 150
+                })^",
+                "subnet configuration failed: cannot specify both ddns-ttl-max and ddns-ttl"
+            },{
+                __LINE__,
+                R"^({
+                    "id": 1,
+                    "ddns-ttl-min": 150,
+                    "ddns-ttl-max": 25
+                })^",
+                "subnet configuration failed: ddns-ttl-max: 25 must be greater than ddns-ttl-min: 150"
+            }};
 
         ElementPtr subnet_elem = Element::create(family == AF_INET ?
                                                  "192.0.2.0/24" : "2001:db8::/64");
-	    for (const auto& scenario : scenarios) {
-	        std::stringstream oss;
-	        oss << "scenario at " << scenario.line_no_;
-	        SCOPED_TRACE(oss.str());
+            for (const auto& scenario : scenarios) {
+                std::stringstream oss;
+                oss << "scenario at " << scenario.line_no_;
+                SCOPED_TRACE(oss.str());
 
-	        // Parse configuration specified above.
-	        ElementPtr config_element;
-	        ASSERT_NO_THROW_LOG(config_element = Element::fromJSON(scenario.json_));
+                // Parse configuration specified above.
+                ElementPtr config_element;
+                ASSERT_NO_THROW_LOG(config_element = Element::fromJSON(scenario.json_));
             config_element->set("subnet", subnet_elem);
-	        ParserType parser(family);
-	        ASSERT_THROW_MSG(parser.parse(config_element), DhcpConfigError, scenario.exp_message_);
-	    }
-	}
+                ParserType parser(family);
+                ASSERT_THROW_MSG(parser.parse(config_element), DhcpConfigError, scenario.exp_message_);
+            }
+        }
 
     /// @brief Tests valid DDNS parameters in v4 or v6 pools.
     ///
@@ -241,7 +241,7 @@ public:
     /// @param pool1 string pool specification for the first pool
     /// @param pool2 string pool specification for the first pool
     template<typename PoolListParserType>
-	void validPoolDdnsParameters(const std::string& pool1, const std::string& pool2) {
+        void validPoolDdnsParameters(const std::string& pool1, const std::string& pool2) {
         std::stringstream ss;
 
         ss <<
@@ -456,8 +456,8 @@ public:
     /// @brief Sets the Hooks path from which hooks can be loaded.
     /// @param custom_path path to use as the hooks path.
     void setHooksTestPath(const std::string explicit_path = "") {
-        HooksLibrariesParser::getHooksPath(true, 
-                                           (!explicit_path.empty() ? 
+        HooksLibrariesParser::getHooksPath(true,
+                                           (!explicit_path.empty() ?
                                            explicit_path : DHCPSRV_HOOKS_TEST_PATH));
     }
 
@@ -4472,12 +4472,12 @@ TEST_F(DhcpParserTest, invalidDdnsTtlParmatersSubnet6) {
 
 // Verifies valid DDNS parameters in v4 pools.
 TEST_F(DhcpParserTest, validDdnsParmatersPool4) {
-	validPoolDdnsParameters<Pools4ListParser>("192.0.1.0/24", "192.0.2.0/24");
+        validPoolDdnsParameters<Pools4ListParser>("192.0.1.0/24", "192.0.2.0/24");
 }
 
 // Verifies valid DDNS parameters in v6 pools.
 TEST_F(DhcpParserTest, validDdnsParmatersPool6) {
-	validPoolDdnsParameters<Pools6ListParser>("2001:db8:1::/64", "2001:db8:2::/64");
+        validPoolDdnsParameters<Pools6ListParser>("2001:db8:1::/64", "2001:db8:2::/64");
 }
 
 }  // Anonymous namespace

src/lib/dhcpsrv/tests/flq_allocation_state_unittest.cc

@@ -39,12 +39,15 @@ TEST(PoolFreeLeaseAllocationState, addDeleteFreeLeaseV4) {
 
     // Add the first free lease. The pool should now have one free lease
     // that is always offered.
+    EXPECT_FALSE(state->isFreeLease(IOAddress("192.0.2.1")));
     state->addFreeLease(IOAddress("192.0.2.1"));
     EXPECT_FALSE(state->exhausted());
     EXPECT_EQ(1, state->getFreeLeaseCount());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("192.0.2.1")));
     // The same lease is always offered.
     EXPECT_EQ("192.0.2.1", state->offerFreeLease().toText());
     EXPECT_EQ("192.0.2.1", state->offerFreeLease().toText());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("192.0.2.1")));
 
     // Add another free lease. We should now have two free leases.
     state->addFreeLease(IOAddress("192.0.2.3"));
@@ -55,9 +58,12 @@ TEST(PoolFreeLeaseAllocationState, addDeleteFreeLeaseV4) {
     EXPECT_EQ("192.0.2.1", state->offerFreeLease().toText());
     // Now, the second lease should be offered.
     EXPECT_EQ("192.0.2.3", state->offerFreeLease().toText());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("192.0.2.1")));
+    EXPECT_TRUE(state->isFreeLease(IOAddress("192.0.2.3")));
 
     // Try to delete a non-existing lease. It should not affect the
     // existing leases.
+    EXPECT_FALSE(state->isFreeLease(IOAddress("192.0.2.2")));
     state->deleteFreeLease(IOAddress("192.0.2.2"));
     EXPECT_FALSE(state->exhausted());
     EXPECT_EQ(2, state->getFreeLeaseCount());
@@ -126,12 +132,15 @@ TEST(PoolFreeLeaseAllocationState, addDeleteFreeLeaseNA) {
 
     // Add the first free lease. The pool should now have one free lease
     // that is always offered.
+    EXPECT_FALSE(state->isFreeLease(IOAddress("2001:db8:1::1")));
     state->addFreeLease(IOAddress("2001:db8:1::1"));
     EXPECT_FALSE(state->exhausted());
     EXPECT_EQ(1, state->getFreeLeaseCount());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("2001:db8:1::1")));
     // The same lease is always offered.
     EXPECT_EQ("2001:db8:1::1", state->offerFreeLease().toText());
     EXPECT_EQ("2001:db8:1::1", state->offerFreeLease().toText());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("2001:db8:1::1")));
 
     // Add another free lease. We should now have two free leases.
     state->addFreeLease(IOAddress("2001:db8:1::3"));
@@ -142,9 +151,12 @@ TEST(PoolFreeLeaseAllocationState, addDeleteFreeLeaseNA) {
     EXPECT_EQ("2001:db8:1::1", state->offerFreeLease().toText());
     // Now, the second lease should be offered.
     EXPECT_EQ("2001:db8:1::3", state->offerFreeLease().toText());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("2001:db8:1::1")));
+    EXPECT_TRUE(state->isFreeLease(IOAddress("2001:db8:1::3")));
 
     // Try to delete a non-existing lease. It should not affect the
     // existing leases.
+    EXPECT_FALSE(state->isFreeLease(IOAddress("2001:db8:1::2")));
     state->deleteFreeLease(IOAddress("2001:db8:1::2"));
     EXPECT_FALSE(state->exhausted());
     EXPECT_EQ(2, state->getFreeLeaseCount());
@@ -211,11 +223,15 @@ TEST(PoolFreeLeaseAllocationState, addDeleteFreeLeasePD) {
 
     // Add the first free lease. The pool should now have one free lease
     // that is always offered.
+    EXPECT_FALSE(state->isFreeLease(IOAddress("3000::5600")));
     state->addFreeLease(IOAddress("3000::5600"));
     EXPECT_FALSE(state->exhausted());
     EXPECT_EQ(1, state->getFreeLeaseCount());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("3000::5600")));
     // The same lease is always offered.
     EXPECT_EQ("3000::5600", state->offerFreeLease().toText());
+    EXPECT_EQ("3000::5600", state->offerFreeLease().toText());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("3000::5600")));
 
     // Add another free lease. We should now have two free leases.
     state->addFreeLease(IOAddress("3000::7800"));
@@ -226,9 +242,12 @@ TEST(PoolFreeLeaseAllocationState, addDeleteFreeLeasePD) {
     EXPECT_EQ("3000::5600", state->offerFreeLease().toText());
     // Now, the second lease should be offered.
     EXPECT_EQ("3000::7800", state->offerFreeLease().toText());
+    EXPECT_TRUE(state->isFreeLease(IOAddress("3000::5600")));
+    EXPECT_TRUE(state->isFreeLease(IOAddress("3000::7800")));
 
     // Try to delete a non-existing lease. It should not affect the
     // existing leases.
+    EXPECT_FALSE(state->isFreeLease(IOAddress("3000::6400")));
     state->deleteFreeLease(IOAddress("3000::6400"));
     EXPECT_FALSE(state->exhausted());
     EXPECT_EQ(2, state->getFreeLeaseCount());
@@ -274,5 +293,4 @@ TEST(PoolFreeLeaseAllocationState, addFreeLeasPDSeveralTimes) {
     EXPECT_TRUE(state->exhausted());
 }
 
-
 } // end of anonymous namespace

src/lib/dhcpsrv/tests/flq_allocator_unittest.cc

@@ -65,6 +65,11 @@ TEST_F(FreeLeaseQueueAllocatorTest4, populateFreeAddressLeases) {
     ASSERT_TRUE(pool_state);
     EXPECT_FALSE(pool_state->exhausted());
 
+    double r = alloc.getOccupancyRate(IOAddress("192.0.2.101"), cc_);
+    EXPECT_EQ(.6, r);
+    r = alloc.getOccupancyRate(IOAddress("192.0.2.1"), cc_);
+    EXPECT_EQ(0., r);
+
     std::set<IOAddress> addresses;
     for (auto i = 0; i < 5; ++i) {
         auto lease = pool_state->offerFreeLease();
@@ -124,6 +129,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, singlePoolWithAllocations) {
     IOAddress candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
     EXPECT_TRUE(candidate.isV4Zero());
 
+    double r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(1., r);
+
     auto i = 0;
     for (auto const& address_lease : leases) {
         if (i % 2) {
@@ -132,6 +140,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, singlePoolWithAllocations) {
         ++i;
     }
 
+    r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(.5, r);
+
     for (auto j = 0; j < 5; ++j) {
         candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
         EXPECT_TRUE(subnet_->inPool(Lease::TYPE_V4, candidate));
@@ -142,6 +153,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, singlePoolWithAllocations) {
 
     candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
     EXPECT_TRUE(candidate.isV4Zero());
+
+    r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(1., r);
 }
 
 // Test allocating IPv4 addresses and re-allocating these that are
@@ -170,6 +184,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, singlePoolWithReclamations) {
     IOAddress candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
     EXPECT_TRUE(candidate.isV4Zero());
 
+    double r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(1., r);
+
     auto i = 0;
     for (auto const& address_lease : leases) {
         if (i % 2) {
@@ -179,6 +196,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, singlePoolWithReclamations) {
         }
         ++i;
     }
+    r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(.5, r);
+
     for (auto j = 0; j < 5; ++j) {
         candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
         EXPECT_TRUE(subnet_->inPool(Lease::TYPE_V4, candidate));
@@ -187,9 +207,11 @@ TEST_F(FreeLeaseQueueAllocatorTest4, singlePoolWithReclamations) {
         lease->state_ = Lease::STATE_DEFAULT;
         EXPECT_NO_THROW(lease_mgr.updateLease4(lease));
     }
-
     candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
     EXPECT_TRUE(candidate.isV4Zero());
+
+    r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(1., r);
 }
 
 // Test allocating DHCPv4 leases for many pools in a subnet.
@@ -213,6 +235,10 @@ TEST_F(FreeLeaseQueueAllocatorTest4, manyPools) {
 
     auto& lease_mgr = LeaseMgrFactory::instance();
 
+    double r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    // 1/100
+    EXPECT_EQ(.01, r);
+
     std::set<IOAddress> addresses_set;
     std::vector<IOAddress> addresses_vector;
     std::vector<PoolPtr> pools_vector;
@@ -232,6 +258,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, manyPools) {
     // Make sure that unique addresses have been returned.
     EXPECT_EQ(total, addresses_set.size());
 
+    r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(1., r);
+
     // Verify that the addresses are returned in the random order.
     // Count how many times we found consecutive addresses. It should
     // be 0 or close to 0.
@@ -263,12 +292,16 @@ TEST_F(FreeLeaseQueueAllocatorTest4, manyPools) {
 // Test that the allocator returns a zero address when there are no pools
 // in a subnet.
 TEST_F(FreeLeaseQueueAllocatorTest4, noPools) {
-   FreeLeaseQueueAllocator alloc(Lease::TYPE_V4, subnet_);
+    FreeLeaseQueueAllocator alloc(Lease::TYPE_V4, subnet_);
 
-   subnet_->delPools(Lease::TYPE_V4);
+    subnet_->delPools(Lease::TYPE_V4);
 
-   IOAddress candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
-   EXPECT_TRUE(candidate.isV4Zero());
+    IOAddress candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
+    EXPECT_TRUE(candidate.isV4Zero());
+
+    // rate is 0. because of the address can't be found, not from 0./0....
+    double r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+    EXPECT_EQ(0., r);
 }
 
 // Test that the allocator respects client class guards.
@@ -304,6 +337,9 @@ TEST_F(FreeLeaseQueueAllocatorTest4, clientClasses) {
 
    // Simulate client's request belonging to the class bar.
    cc_.insert("bar");
+   double r = alloc.getOccupancyRate(IOAddress("192.0.2.120"), cc_);
+   // 1/20
+   EXPECT_EQ(.05, r);
    for (auto i = 0; i < 20; ++i) {
        // Allocate random addresses and make sure they belong to the
        // pools associated with the class bar.
@@ -315,11 +351,17 @@ TEST_F(FreeLeaseQueueAllocatorTest4, clientClasses) {
    }
    EXPECT_EQ(20, addresses_set.size());
 
+   r = alloc.getOccupancyRate(IOAddress("192.0.2.120"), cc_);
+   EXPECT_EQ(1., r);
+
    addresses_set.clear();
 
    // Simulate the case that the client also belongs to the class foo.
    // All pools should now be available.
    cc_.insert("foo");
+   r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+   // 21/40
+   EXPECT_EQ(.525, r);
    for (auto i = 0; i < 20; ++i) {
        IOAddress candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
        addresses_set.insert(candidate);
@@ -327,12 +369,16 @@ TEST_F(FreeLeaseQueueAllocatorTest4, clientClasses) {
        EXPECT_TRUE(subnet_->inRange(candidate));
    }
    EXPECT_EQ(20, addresses_set.size());
+   r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+   EXPECT_EQ(1., r);
 
    // When the client does not belong to any client class the allocator
    // can't offer any address to the client.
    cc_.clear();
    IOAddress candidate = alloc.pickAddress(cc_, clientid_, IOAddress("0.0.0.0"));
    EXPECT_TRUE(candidate.isV4Zero());
+   r = alloc.getOccupancyRate(IOAddress("192.0.2.100"), cc_);
+   EXPECT_EQ(0., r);
 }
 
 /// @brief Test fixture class for the DHCPv6 Free Lease Queue allocator.
@@ -382,6 +428,10 @@ TEST_F(FreeLeaseQueueAllocatorTest6, populateFreeAddressLeases) {
 
     EXPECT_NO_THROW(alloc.initAfterConfigure());
 
+    // Address getOccupancyRate is for IPv4 only.
+    double r = alloc.getOccupancyRate(IOAddress("2001:db8:1::10"), cc_);
+    EXPECT_EQ(0., r);
+
     auto pool_state = boost::dynamic_pointer_cast<PoolFreeLeaseQueueAllocationState>(pool_->getAllocationState());
     ASSERT_TRUE(pool_state);
     EXPECT_FALSE(pool_state->exhausted());
@@ -461,7 +511,7 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePoolWithAllocations) {
     }
 
     for (auto j = 0; j < 8; ++j) {
-	candidate = alloc.pickAddress(cc_, duid_, IOAddress("::"));
+        candidate = alloc.pickAddress(cc_, duid_, IOAddress("::"));
         EXPECT_TRUE(subnet_->inPool(Lease::TYPE_NA, candidate));
         EXPECT_TRUE(subnet_->inPool(Lease::TYPE_NA, candidate, cc_));
         auto lease = createLease6(Lease::TYPE_NA, candidate, i);
@@ -509,7 +559,7 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePoolWithReclamations) {
     }
 
     for (auto j = 0; j < 8; ++j) {
-	candidate = alloc.pickAddress(cc_, duid_, IOAddress("::"));
+        candidate = alloc.pickAddress(cc_, duid_, IOAddress("::"));
         EXPECT_TRUE(subnet_->inPool(Lease::TYPE_NA, candidate));
         EXPECT_TRUE(subnet_->inPool(Lease::TYPE_NA, candidate, cc_));
         auto lease = lease_mgr.getLease6(Lease::TYPE_NA, candidate);
@@ -686,6 +736,9 @@ TEST_F(FreeLeaseQueueAllocatorTest6, populateFreePrefixDelegationLeases) {
     ASSERT_TRUE(pool_state);
     EXPECT_FALSE(pool_state->exhausted());
 
+    double r = alloc.getOccupancyRate(IOAddress("2001:db8:2::"), 128, cc_);
+    EXPECT_EQ(5. / 256., r);
+
     std::set<IOAddress> addresses;
     for (auto i = 0; i < 256; ++i) {
         auto lease = pool_state->offerFreeLease();
@@ -721,9 +774,12 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPool) {
     }
     // The pool comprises 65536 prefixes. All should be returned.
     EXPECT_EQ(65536, prefixes.size());
+
+    double r = alloc.getOccupancyRate(IOAddress("2001:db8:1:2::"), 128, cc_);
+    EXPECT_EQ(1., r);
 }
 
-// Test allocating IPv6 addresses and re-allocating these that are
+// Test allocating delegated prefixes and re-allocating these that are
 // deleted (released).
 TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithAllocations) {
     // Remove the default pool because it is too large for this test case.
@@ -757,6 +813,8 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithAllocations) {
 
     IOAddress candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 0);
     EXPECT_TRUE(candidate.isV6Zero());
+    double r = alloc.getOccupancyRate(IOAddress("3000::"), 128, cc_);
+    EXPECT_EQ(1., r);
 
     auto i = 0;
     for (auto const& address_lease : leases) {
@@ -765,6 +823,8 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithAllocations) {
         }
         ++i;
     }
+    r = alloc.getOccupancyRate(IOAddress("3000::"), 128, cc_);
+    EXPECT_EQ(.5, r);
 
     for (auto j = 0; j < 128; ++j) {
         candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 0);
@@ -776,9 +836,12 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithAllocations) {
 
     candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 0);
     EXPECT_TRUE(candidate.isV6Zero());
+
+    r = alloc.getOccupancyRate(IOAddress("3000::"), 128, cc_);
+    EXPECT_EQ(1., r);
 }
 
-// Test allocating IPv6 addresses and re-allocating these that are
+// Test allocating delegated prefixes and re-allocating these that are
 // reclaimed.
 TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithReclamations) {
     // Remove the default pool because it is too large for this test case.
@@ -812,6 +875,8 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithReclamations) {
 
     IOAddress candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 0);
     EXPECT_TRUE(candidate.isV6Zero());
+    double r = alloc.getOccupancyRate(IOAddress("3000::"), 128, cc_);
+    EXPECT_EQ(1., r);
 
     auto i = 0;
     for (auto const& address_lease : leases) {
@@ -822,6 +887,8 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithReclamations) {
         }
         ++i;
     }
+    r = alloc.getOccupancyRate(IOAddress("3000::"), 128, cc_);
+    EXPECT_EQ(.5, r);
 
     for (auto j = 0; j < 128; ++j) {
         candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 0);
@@ -834,8 +901,10 @@ TEST_F(FreeLeaseQueueAllocatorTest6, singlePdPoolWithReclamations) {
 
     candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 0);
     EXPECT_TRUE(candidate.isV6Zero());
-}
 
+        r = alloc.getOccupancyRate(IOAddress("3000::"), 128, cc_);
+    EXPECT_EQ(1., r);
+}
 
 // Test allocating delegated prefixes from multiple pools.
 TEST_F(FreeLeaseQueueAllocatorTest6, manyPdPools) {
@@ -869,6 +938,9 @@ TEST_F(FreeLeaseQueueAllocatorTest6, manyPdPools) {
     }
     // Make sure that unique prefixes have been returned.
     EXPECT_EQ(total, prefixes.size());
+
+    double r = alloc.getOccupancyRate(IOAddress("3001::"), 128, cc_);
+    EXPECT_EQ(1., r);
 }
 
 // Test allocating delegated prefixes from multiple pools.
@@ -890,7 +962,6 @@ TEST_F(FreeLeaseQueueAllocatorTest6, manyPdPoolsPreferLower) {
     ASSERT_NO_THROW(alloc.initAfterConfigure());
     auto& lease_mgr = LeaseMgrFactory::instance();
 
-
     Pool6Ptr pool;
 
     std::set<IOAddress> prefixes;
@@ -904,6 +975,13 @@ TEST_F(FreeLeaseQueueAllocatorTest6, manyPdPoolsPreferLower) {
     }
     // Make sure that unique prefixes have been returned.
     EXPECT_EQ(total, prefixes.size());
+
+    double r = alloc.getOccupancyRate(IOAddress("2001:db8:1:2::"), 120, cc_);
+    EXPECT_EQ(1., r);
+    r = alloc.getOccupancyRate(IOAddress("2001:db8:1:2::"), 128, cc_);
+    EXPECT_EQ(65536. / 68096., r);
+    r = alloc.getOccupancyRate(IOAddress("2001:db8:1:2::"), 64, cc_);
+    EXPECT_EQ(0., r);
 }
 
 // Test allocating delegated prefixes from multiple pools.
@@ -938,6 +1016,8 @@ TEST_F(FreeLeaseQueueAllocatorTest6, manyPdPoolsPreferEqual) {
     }
     // Make sure that unique prefixes have been returned.
     EXPECT_EQ(total, prefixes.size());
+    double r = alloc.getOccupancyRate(IOAddress("3001::"), 128, cc_);
+    EXPECT_EQ(2560. / 68096., r);
 }
 
 // Test allocating delegated prefixes from multiple pools.
@@ -972,6 +1052,8 @@ TEST_F(FreeLeaseQueueAllocatorTest6, manyPdPoolsPreferHigher) {
     }
     // Make sure that unique prefixes have been returned.
     EXPECT_EQ(total, prefixes.size());
+    double r = alloc.getOccupancyRate(IOAddress("3001::"), 128, cc_);
+    EXPECT_EQ(2560. / 68096., r);
 }
 
 // Test that the allocator respects client class guards.
@@ -1008,8 +1090,16 @@ TEST_F(FreeLeaseQueueAllocatorTest6, pdPoolsClientClasses) {
 
     candidate = alloc.pickPrefix(cc_, pool, duid_, Allocator::PREFIX_LEN_HIGHER, IOAddress("::"), 64);
     EXPECT_TRUE(candidate.isV6Zero());
-}
 
+    double r = alloc.getOccupancyRate(IOAddress("3000:1::"), 128, cc_);
+    EXPECT_EQ(1., r);
+    cc_.insert("foo");
+    r = alloc.getOccupancyRate(IOAddress("3000:1::"), 128, cc_);
+    EXPECT_EQ(256. / 65792., r);
+    cc_.clear();
+    r = alloc.getOccupancyRate(IOAddress("3000:1::"), 128, cc_);
+    EXPECT_EQ(0., r);
+}
 
 } // end of isc::dhcp::test namespace
 } // end of isc::dhcp namespace

src/lib/dhcpsrv/tests/network_unittest.cc

@@ -186,6 +186,7 @@ TEST_F(NetworkTest, inheritanceSupport4) {
     globals_->set("ddns-ttl", Element::create(400));
     globals_->set("ddns-ttl-min", Element::create(200));
     globals_->set("ddns-ttl-max", Element::create(600));
+    globals_->set("adaptive-lease-time-threshold", Element::create(.90));
 
     // For each parameter for which inheritance is supported run
     // the test that checks if the values are inherited properly.
@@ -393,6 +394,12 @@ TEST_F(NetworkTest, inheritanceSupport4) {
                                              &Network::setDdnsTtlMax,
                                              500, 600);
     }
+    {
+        SCOPED_TRACE("adaptive-lease-time-threshold");
+        testNetworkInheritance<TestNetwork4>(&Network::getAdaptiveLeaseTimeThreshold,
+                                             &Network::setAdaptiveLeaseTimeThreshold,
+                                             .80, .90);
+    }
 }
 
 // This test verifies that the inheritance is supported for DHCPv6
@@ -420,6 +427,7 @@ TEST_F(NetworkTest, inheritanceSupport6) {
     globals_->set("ddns-ttl-max", Element::create(600));
     globals_->set("cache-threshold", Element::create(.35));
     globals_->set("cache-max-age", Element::create(20));
+    globals_->set("adaptive-lease-time-threshold", Element::create(.90));
 
     // For each parameter for which inheritance is supported run
     // the test that checks if the values are inherited properly.
@@ -558,6 +566,12 @@ TEST_F(NetworkTest, inheritanceSupport6) {
                                              &Network::setCacheMaxAge,
                                              10, 20);
     }
+    {
+        SCOPED_TRACE("adaptive-lease-time-threshold");
+        testNetworkInheritance<TestNetwork4>(&Network::getAdaptiveLeaseTimeThreshold,
+                                             &Network::setAdaptiveLeaseTimeThreshold,
+                                             .80, .90);
+    }
 
     // Interface-id requires special type of test.
     boost::shared_ptr<TestNetwork6> net_child(new TestNetwork6());

src/lib/dhcpsrv/tests/shared_network_parser_unittest.cc

@@ -299,6 +299,7 @@ public:
                 "    \"store-extended-info\": true,"
                 "    \"cache-threshold\": 0.123,"
                 "    \"cache-max-age\": 123,"
+                "    \"adaptive-lease-time-threshold\": .90,"
                 "    \"offer-lifetime\": 777,"
                 "    \"ddns-update-on-renew\": true,"
                 "    \"option-data\": ["
@@ -336,7 +337,8 @@ public:
                 "            \"hostname-char-set\": \"\","
                 "            \"cache-threshold\": .20,"
                 "            \"cache-max-age\": 50,"
-                "            \"allocator\": \"random\""
+                "            \"allocator\": \"random\","
+                "            \"adaptive-lease-time-threshold\": .80"
                 "        },"
                 "        {"
                 "            \"id\": 2,"
@@ -362,7 +364,8 @@ public:
                 "            \"t1-percent\": .40,"
                 "            \"t2-percent\": .80,"
                 "            \"cache-threshold\": 0.0,"
-                "            \"cache-max-age\": 0"
+                "            \"cache-max-age\": 0,"
+                "            \"adaptive-lease-time-threshold\": .70"
                 "        }"
                 "    ]"
                 "}";
@@ -432,6 +435,7 @@ TEST_F(SharedNetwork4ParserTest, parse) {
     EXPECT_EQ(777, network->getOfferLft().get());
     EXPECT_TRUE(network->getDdnsUpdateOnRenew().get());
     EXPECT_EQ("iterative", network->getAllocatorType().get());
+    EXPECT_EQ(.90, network->getAdaptiveLeaseTimeThreshold().get());
 
     // Relay information.
     auto relay_info = network->getRelayInfo();
@@ -730,6 +734,7 @@ public:
                 "    \"ddns-update-on-renew\": true,"
                 "    \"allocator\": \"random\","
                 "    \"pd-allocator\": \"iterative\","
+                "    \"adaptive-lease-time-threshold\": .90,"
                 "    \"option-data\": ["
                 "        {"
                 "            \"name\": \"dns-servers\","
@@ -845,6 +850,7 @@ TEST_F(SharedNetwork6ParserTest, parse) {
     EXPECT_TRUE(network->getDdnsUpdateOnRenew().get());
     EXPECT_EQ("random", network->getAllocatorType().get());
     EXPECT_EQ("iterative", network->getPdAllocatorType().get());
+    EXPECT_EQ(.90, network->getAdaptiveLeaseTimeThreshold().get());
 
     // Relay information.
     auto relay_info = network->getRelayInfo();

src/lib/util/filesystem.h

@@ -246,7 +246,7 @@ public:
     /// @return validated path as a string (supported path + input file name)
     ///
     /// @throw BadValue if the input path does not include a file name.
-    /// @trhow SecurityError if the parent path does not path the supported path and
+    /// @throw SecurityError if the parent path does not path the supported path and
     /// security is being enforced, SecurityWarn if it is not being enforced.
     std::string validatePath(const std::string input_path_str,
                              bool enforce_path = shouldEnforceSecurity()) const;