[3564] Resolve conflicts with the reserved addresses in allocation engine.

src/lib/dhcpsrv/alloc_engine.cc

@@ -524,50 +524,90 @@ AllocEngine::allocateLease4(const SubnetPtr& subnet, const ClientIdPtr& clientid
         ctx.old_lease_ = old_lease;
         ctx.host_ = HostMgr::instance().get4(subnet->getID(), hwaddr);
 
+        // If there is a reservation for this client we want to allocate the
+        // reserved address to the client, rather than any other address.
         if (ctx.host_) {
+            // In some cases the client doesn't supply any address, e.g. when
+            // it sends a DHCPDISCOVER. In such cases, we use the reserved
+            // address as a hint.
             if (ctx.hint_ == IOAddress("0.0.0.0")) {
                 ctx.hint_ = ctx.host_->getIPv4Reservation();
 
+            // If the client supplied an address we have to check if this
+            // address is reserved for this client. If not, we will send
+            // DHCPNAK to inform the client that we were not able to
+            // assign a requested address. The fake allocation (DHCPDISCOVER
+            // case) is an exception. In such case we treat the address
+            // supplied by the client as a hint, but we may offer address
+            // other than desired by the client. So, we don't return an
+            // empty lease.
             } else if (!ctx.fake_allocation_ &&
                        (ctx.hint_ != ctx.host_->getIPv4Reservation())) {
                 return (Lease4Ptr());
             }
         }
 
+        // Check if the client has any leases in the lease database, using HW
+        // address or client identifier.
         LeaseMgr& lease_mgr = LeaseMgrFactory::instance();
         Lease4Ptr existing = lease_mgr.getLease4(*hwaddr, ctx.subnet_->getID());
         if (!existing && clientid) {
             existing = lease_mgr.getLease4(*clientid, ctx.subnet_->getID());
         }
 
+        // If client has a lease there are two choices. The server may need
+        // to renew (no address change) the lease. Or, the server may need
+        // to replace the lease with a different one. This is the case when
+        // the server has a dynamically assigned lease but an administrator
+        // has made a new reservation for the client for a different address.
         if (existing) {
             existing = reallocateClientLease(existing, ctx);
-            if (ctx.host_ || existing) {
+            // The interrupt_processing_ flag indicates that the lease
+            // reallocation was not successful and that the allocation
+            // engine should cease allocation process for this client.
+            // This may occur when the client is trying to renew the
+            // lease which is reserved for someone else. The server should
+            // send DHCPNAK to indicate that the client should try to
+            // start over the allocation process.
+            if (ctx.interrupt_processing_) {
+                old_lease = ctx.old_lease_;
+                return (Lease4Ptr());
+
+            // If we tried to reallocate the reserved lease we return
+            // at this point regardless if reallocation failed or passed.
+            // We also return when allocation passed, no matter if this
+            // was a reserved address or not.
+            } else  if (ctx.host_ || existing) {
                 old_lease = ctx.old_lease_;
                 return (existing);
             }
         }
 
-        // Check if we have a specific address we would like to allocate for the
-        // client. It may either be an address which the client is currently
-        // using, or it may be a administratively reserved address.
-        if (ctx.host_ || subnet->inPool(Lease::TYPE_V4, hint)) {
+        // There is no lease in the database for this client, so we will
+        // proceed with a new allocation. We will try to allocate a
+        // reserved address or an address from a dynamic pool if there is
+        // no reservation.
+        if (ctx.host_ || subnet->inPool(Lease::TYPE_V4, ctx.hint_)) {
             // If a client is requesting specific IP address, but the
             // reservation was made for a different address the server returns
             // NAK to the client. By returning NULL lease here we indicate to
             // the server that we're not able to fulfil client's request for the
-            // particular IP address.
+            // particular IP address. We don't return NULL lease in case of the
+            // fake allocation (DHCPDISCOVER) because in this case the address
+            // supplied by the client is only a hint.
             if (!ctx.fake_allocation_ && ctx.host_ &&
-                (hint != IOAddress("0.0.0.0")) &&
-                (ctx.host_->getIPv4Reservation() != hint)) {
+                (ctx.hint_ != IOAddress("0.0.0.0")) &&
+                (ctx.host_->getIPv4Reservation() != ctx.hint_)) {
                 return (Lease4Ptr());
             }
 
-            // The reserved address always takes precedence over hints. But, if
-            // there is no reservation, try to respect the client's hint.
+            // The reserved address always takes precedence over an address
+            // supplied by the client (renewed address or requested).
             const IOAddress& candidate = ctx.host_ ?
-                ctx.host_->getIPv4Reservation() : hint;
+                ctx.host_->getIPv4Reservation() : ctx.hint_;
 
+            // Once we picked an address we want to allocate, we have to check
+            // if this address is available.
             existing = LeaseMgrFactory::instance().getLease4(candidate);
             if (!existing) {
                 // The candidate address is currently unused. Let's create a
@@ -588,14 +628,21 @@ AllocEngine::allocateLease4(const SubnetPtr& subnet, const ClientIdPtr& clientid
                     return (lease);
                 }
 
+            // There is a lease for this address in the lease database but
+            // it is possible that the lease has expired, in which case
+            // we will be able to reuse it.
             } else {
                 if (existing->expired()) {
                     // Save the old lease, before reusing it.
                     old_lease.reset(new Lease4(*existing));
                     return (reuseExpiredLease(existing, ctx));
 
-                } else if (ctx.host_ && (ctx.host_->getIPv4Reservation() !=
-                                         IOAddress("0.0.0.0"))) {
+                // The existing lease is not expired (is in use by some
+                // other client). If we are trying to get this lease because
+                // the address has been reserved for the client we have no
+                // choice but to return a NULL lease to indicate that the
+                // allocation has failed.
+                } else if (ctx.host_) {
                     return (Lease4Ptr());
 
                 }
@@ -621,10 +668,15 @@ AllocEngine::allocateLease4(const SubnetPtr& subnet, const ClientIdPtr& clientid
 
         unsigned int i = attempts_;
         do {
-            IOAddress candidate = allocator->pickAddress(subnet, clientid, hint);
-
-            /// @todo: check if the address is reserved once we have host support
-            /// implemented
+            IOAddress candidate = allocator->pickAddress(subnet, clientid, ctx.hint_);
+
+            // Check if this address is reserved. There is no need to check for
+            // whom it is reserved, because if it has been reserved for us we would
+            // have already allocated a lease.
+            if (HostMgr::instance().get4(subnet->getID(), candidate)) {
+                // Don't allocate a reserved address.
+                continue;
+            }
 
             Lease4Ptr existing = LeaseMgrFactory::instance().getLease4(candidate);
             if (!existing) {
@@ -667,11 +719,25 @@ AllocEngine::allocateLease4(const SubnetPtr& subnet, const ClientIdPtr& clientid
 
 Lease4Ptr
 AllocEngine::renewLease4(const Lease4Ptr& lease,
-                         const AllocEngine::Context4& ctx) {
+                         AllocEngine::Context4& ctx) {
     if (!lease) {
         isc_throw(BadValue, "null lease specified for renewLease4");
     }
 
+    // The ctx.host_ possibly contains a reservation for the client for which
+    // we are renewing a lease. If this reservation exists, we assume that
+    // there is no conflict in assigning the address to this client. Note
+    // that the reallocateClientLease checks if the address reserved for
+    // the client matches the address in the lease we're renewing here.
+    if (!ctx.host_) {
+        ConstHostPtr host = HostMgr::instance().get4(ctx.subnet_->getID(),
+                                                     lease->addr_);
+        if (host && ctx.hwaddr_ && (*host->getHWAddress() != *ctx.hwaddr_)) {
+            ctx.interrupt_processing_ = !ctx.fake_allocation_;
+            return (Lease4Ptr());
+        }
+    }
+
     // Let's keep the old data. This is essential if we are using memfile
     // (the lease returned points directly to the lease4 object in the database)
     // We'll need it if we want to skip update (i.e. roll back renewal)
@@ -815,7 +881,7 @@ Lease6Ptr AllocEngine::reuseExpiredLease(Lease6Ptr& expired,
 
 Lease4Ptr
 AllocEngine::reuseExpiredLease(Lease4Ptr& expired,
-                               const AllocEngine::Context4& ctx) {
+                               AllocEngine::Context4& ctx) {
     if (!expired) {
         isc_throw(BadValue, "null lease specified for reuseExpiredLease");
     }
@@ -884,7 +950,8 @@ AllocEngine::reuseExpiredLease(Lease4Ptr& expired,
 }
 
 Lease4Ptr
-AllocEngine::replaceClientLease(Lease4Ptr& lease, const Context4& ctx) {
+AllocEngine::replaceClientLease(Lease4Ptr& lease, Context4& ctx) {
+
     if (!lease) {
         isc_throw(BadValue, "null lease specified for replaceClientLease");
     }
@@ -893,18 +960,28 @@ AllocEngine::replaceClientLease(Lease4Ptr& lease, const Context4& ctx) {
         isc_throw(BadValue, "null subnet specified for replaceClientLease");
     }
 
-    if (!ctx.host_) {
-        isc_throw(BadValue, "null host specified for replaceClientLease");
-    }
-
     if (ctx.hint_ == IOAddress("0.0.0.0")) {
         isc_throw(BadValue, "zero address specified for the"
                   " replaceClientLease");
     }
 
     IOAddress prev_address = lease->addr_;
+    if (!ctx.host_) {
+        ConstHostPtr host = HostMgr::instance().get4(ctx.subnet_->getID(),
+                                                     ctx.hint_);
+        if (host && ctx.hwaddr_ && (*host->getHWAddress() != *ctx.hwaddr_)) {
+            ctx.interrupt_processing_ = true;
+            return (Lease4Ptr());
+        }
+        lease->addr_ = ctx.hint_;
+
+    } else {
+        lease->addr_ = ctx.host_->getIPv4Reservation();
+
+    }
+
+
     updateLease4Information(lease, ctx);
-    lease->addr_ = ctx.host_->getIPv4Reservation();
 
     // Execute callouts registered for lease4_select.
     if (ctx.callout_handle_ && HooksManager::getHooksManager()
@@ -949,7 +1026,8 @@ AllocEngine::reallocateClientLease(Lease4Ptr& lease,
     // Save the old lease, before renewal.
     ctx.old_lease_.reset(new Lease4(*lease));
 
-    if (ctx.host_ && ctx.host_->getIPv4Reservation() != lease->addr_) {
+    if ((ctx.host_ && (ctx.host_->getIPv4Reservation() != lease->addr_)) ||
+        (lease->addr_ != ctx.hint_)) {
         lease = replaceClientLease(lease, ctx);
         return (lease);
 
@@ -1146,7 +1224,7 @@ Lease4Ptr AllocEngine::createLease4(const SubnetPtr& subnet,
 
 void
 AllocEngine::updateLease4Information(const Lease4Ptr& lease,
-                                     const AllocEngine::Context4& ctx) const {
+                                     AllocEngine::Context4& ctx) const {
     // This should not happen in theory.
     if (!lease) {
         isc_throw(BadValue, "null lease specified for updateLease4Information");

src/lib/dhcpsrv/alloc_engine.h

@@ -273,12 +273,20 @@ protected:
         /// @brief A pointer to the object identifying host reservations.
         ConstHostPtr host_;
 
+        /// @brief Signals that the allocation should be interrupted.
+        ///
+        /// This flag is set by the downstream methods called by the
+        /// @c AllocEngine::allocateLease4. This flag is set to true to
+        /// indicate that an attempt to allocate a lease should be
+        /// interrupted.
+        bool interrupt_processing_;
+
         /// @brief Default constructor.
         Context4()
             : subnet_(), clientid_(), hwaddr_(), hint_("0.0.0.0"),
               fwd_dns_update_(false), rev_dns_update_(false),
               hostname_(""), callout_handle_(), fake_allocation_(false),
-              old_lease_(), host_() {
+              old_lease_(), host_(), interrupt_processing_(false) {
         }
     };
 
@@ -363,7 +371,7 @@ protected:
     /// @return Returns renewed lease. Note that the lease is only updated when
     /// it is an actual allocation (not processing DHCPDISCOVER message).
     Lease4Ptr
-    renewLease4(const Lease4Ptr& lease, const Context4& ctx);
+    renewLease4(const Lease4Ptr& lease, Context4& ctx);
 
     /// @brief Allocates an IPv6 lease
     ///
@@ -462,7 +470,7 @@ private:
     /// @param ctx A context containing information from the server about the
     /// client and its message.
     void updateLease4Information(const Lease4Ptr& lease,
-                                 const Context4& ctx) const;
+                                 Context4& ctx) const;
 
     /// @brief creates a lease and inserts it in LeaseMgr if necessary
     ///
@@ -515,7 +523,7 @@ private:
     /// @return Updated lease instance.
     /// @throw BadValue if trying to reuse a lease which is still valid or
     /// when the provided parameters are invalid.
-    Lease4Ptr reuseExpiredLease(Lease4Ptr& expired, const Context4& ctx);
+    Lease4Ptr reuseExpiredLease(Lease4Ptr& expired, Context4& ctx);
 
     /// @brief Updates the existing, non expired lease with a information from
     /// the context.
@@ -533,7 +541,7 @@ private:
     ///
     /// @return Pointer to the updated lease.
     /// @throw BadValue if the provided parameters are invalid.
-    Lease4Ptr replaceClientLease(Lease4Ptr& lease, const Context4& ctx);
+    Lease4Ptr replaceClientLease(Lease4Ptr& lease, Context4& ctx);
 
     /// @brief Replace or renew client's lease.
     ///

src/lib/dhcpsrv/base_host_data_source.h

@@ -31,6 +31,14 @@ public:
         isc::Exception(file, line, what) { };
 };
 
+/// @brief Exception thrown when invalid IP address has been specified for
+/// @c Host.
+class BadHostAddress : public isc::BadValue {
+public:
+    BadHostAddress(const char* file, size_t line, const char* what) :
+        isc::BadValue(file, line, what) { };
+};
+
 /// @brief Base interface for the classes implementing simple data source
 /// for host reservations.
 ///
@@ -105,6 +113,26 @@ public:
     get4(const SubnetID& subnet_id, const HWAddrPtr& hwaddr,
          const DuidPtr& duid = DuidPtr()) const = 0;
 
+    /// @brief Returns a host connected to the IPv4 subnet and having
+    /// a reservation for a specified IPv4 address.
+    ///
+    /// One of the use cases for this method is to detect collisions between
+    /// dynamically allocated addresses and reserved addresses. When the new
+    /// address is assigned to a client, the allocation mechanism should check
+    /// if this address is not reserved for some other host and do not allocate
+    /// this address if reservation is present.
+    ///
+    /// Implementations of this method should guard against invalid addresses,
+    /// such as IPv6 address.
+    ///
+    /// @param subnet_id Subnet identifier.
+    /// @param address reserved IPv4 address.
+    ///
+    /// @return Const @c Host object using a specified IPv4 address.
+    virtual ConstHostPtr
+    get4(const SubnetID& subnet_id,
+         const asiolink::IOAddress& address) const = 0;
+
     /// @brief Returns a host connected to the IPv6 subnet.
     ///
     /// Implementations of this method should guard against the case when

src/lib/dhcpsrv/cfg_hosts.cc

@@ -36,13 +36,17 @@ CfgHosts::getAll(const HWAddrPtr& hwaddr, const DuidPtr& duid) {
 }
 
 ConstHostCollection
-CfgHosts::getAll4(const IOAddress&) const {
-    isc_throw(isc::NotImplemented, "getAll4(address) const is not implemented");
+CfgHosts::getAll4(const IOAddress& address) const {
+    ConstHostCollection collection;
+    getAllInternal4<ConstHostCollection>(address, collection);
+    return (collection);
 }
 
 HostCollection
-CfgHosts::getAll4(const IOAddress&) {
-    isc_throw(isc::NotImplemented, "getAll4(address) is not implemented");
+CfgHosts::getAll4(const IOAddress& address) {
+    HostCollection collection;
+    getAllInternal4<HostCollection>(address, collection);
+    return (collection);
 }
 
 template<typename Storage>
@@ -76,6 +80,25 @@ CfgHosts::getAllInternal(const HWAddrPtr& hwaddr, const DuidPtr& duid,
     }
 }
 
+template<typename Storage>
+void
+CfgHosts::getAllInternal4(const IOAddress& address, Storage& storage) const {
+    // Must not specify address other than IPv4.
+    if (!address.isV4()) {
+        isc_throw(BadHostAddress, "must specify an IPv4 address when searching"
+                  " for a host, specified address was " << address);
+    }
+    // Search for the Host using the reserved IPv4 address as a key.
+    const HostContainerIndex1& idx = hosts_.get<1>();
+    HostContainerIndex1Range r = idx.equal_range(address);
+    // Append each Host object to the storage.
+    for (HostContainerIndex1::iterator host = r.first; host != r.second;
+         ++host) {
+        storage.push_back(*host);
+    }
+}
+
+
 ConstHostPtr
 CfgHosts::get4(const SubnetID& subnet_id, const HWAddrPtr& hwaddr,
                const DuidPtr& duid) const {
@@ -90,6 +113,19 @@ CfgHosts::get4(const SubnetID& subnet_id, const HWAddrPtr& hwaddr,
     return (getHostInternal(subnet_id, false, hwaddr, duid));
 }
 
+ConstHostPtr
+CfgHosts::get4(const SubnetID& subnet_id, const IOAddress& address) const {
+    ConstHostCollection hosts = getAll4(address);
+    for (ConstHostCollection::const_iterator host = hosts.begin();
+         host != hosts.end(); ++host) {
+        if ((*host)->getIPv4SubnetID() == subnet_id) {
+            return (*host);
+        }
+    }
+    return (ConstHostPtr());
+}
+
+
 ConstHostPtr
 CfgHosts::get6(const SubnetID& subnet_id, const DuidPtr& duid,
                const HWAddrPtr& hwaddr) const {

src/lib/dhcpsrv/cfg_hosts.h

@@ -80,7 +80,7 @@ public:
     ///
     /// @param address IPv4 address for which the @c Host object is searched.
     ///
-    /// @throw isc::NotImplemented.
+    /// @return Collection of const @c Host objects.
     virtual ConstHostCollection
     getAll4(const asiolink::IOAddress& address) const;
 
@@ -91,7 +91,7 @@ public:
     ///
     /// @param address IPv4 address for which the @c Host object is searched.
     ///
-    /// @throw isc::NotImplemented
+    /// @return Collection of const @c Host objects.
     virtual HostCollection
     getAll4(const asiolink::IOAddress& address);
 
@@ -125,6 +125,16 @@ public:
     get4(const SubnetID& subnet_id, const HWAddrPtr& hwaddr,
          const DuidPtr& duid = DuidPtr());
 
+    /// @brief Returns a host connected to the IPv4 subnet and having
+    /// a reservation for a specified IPv4 address.
+    ///
+    /// @param subnet_id Subnet identifier.
+    /// @param address reserved IPv4 address.
+    ///
+    /// @return Const @c Host object using a specified IPv4 address.
+    virtual ConstHostPtr
+    get4(const SubnetID& subnet_id, const asiolink::IOAddress& address) const;
+
     /// @brief Returns a host connected to the IPv6 subnet and matching
     /// the specified identifiers.
     ///
@@ -216,6 +226,21 @@ private:
     void getAllInternal(const HWAddrPtr& hwaddr, const DuidPtr& duid,
                         Storage& storage) const;
 
+    /// @brief Returns @c Host objects for the specified IPv4 address.
+    ///
+    /// This private method is called by the @c CfgHosts::getAll4 methods
+    /// to retrieve the @c Host for which the specified IPv4 address is
+    /// reserved. The retrieved objects are appended to the @c storage
+    /// container.
+    ///
+    /// @param address IPv4 address.
+    /// @param [out] storage Container to which the retrieved objects are
+    /// appended.
+    /// @tparam One of the @c ConstHostCollection or @c HostCollection.
+    template<typename Storage>
+    void getAllInternal4(const asiolink::IOAddress& address,
+                         Storage& storage) const;
+
     /// @brief Returns @c Host object connected to a subnet.
     ///
     /// This private method returns a pointer to the @c Host object identified

src/lib/dhcpsrv/host_container.h

@@ -64,6 +64,14 @@ typedef boost::multi_index_container<
                     &Host::getIdentifierType
                 >
             >
+        >,
+
+        // Second index is used to search for the host using reserved IPv4
+        // address.
+        boost::multi_index::ordered_non_unique<
+            // Index using values returned by the @c Host::getIPv4Resrvation.
+            boost::multi_index::const_mem_fun<Host, const asiolink::IOAddress&,
+                                               &Host::getIPv4Reservation>
         >
     >
 > HostContainer;
@@ -78,6 +86,16 @@ typedef HostContainer::nth_index<0>::type HostContainerIndex0;
 typedef std::pair<HostContainerIndex0::iterator,
                   HostContainerIndex0::iterator> HostContainerIndex0Range;
 
+/// @brief Second index type in the @c HostContainer.
+///
+/// This index allows for searching for @c Host objects using a
+/// reserved IPv4 address.
+typedef HostContainer::nth_index<1>::type HostContainerIndex1;
+
+/// @brief Results range returned using the @c HostContainerIndex1.
+typedef std::pair<HostContainerIndex1::iterator,
+                  HostContainerIndex1::iterator> HostContainerIndex1Range;
+
 }
 }
 

src/lib/dhcpsrv/host_mgr.cc

@@ -88,6 +88,17 @@ HostMgr::get4(const SubnetID& subnet_id, const HWAddrPtr& hwaddr,
     return (host);
 }
 
+ConstHostPtr
+HostMgr::get4(const SubnetID& subnet_id,
+              const asiolink::IOAddress& address) const {
+    ConstHostPtr host = getCfgHosts()->get4(subnet_id, address);
+    if (!host && alternate_source) {
+        host = alternate_source->get4(subnet_id, address);
+    }
+    return (host);
+}
+
+
 ConstHostPtr
 HostMgr::get6(const SubnetID& subnet_id, const DuidPtr& duid,
                const HWAddrPtr& hwaddr) const {

src/lib/dhcpsrv/host_mgr.h

@@ -139,6 +139,20 @@ public:
     get4(const SubnetID& subnet_id, const HWAddrPtr& hwaddr,
          const DuidPtr& duid = DuidPtr()) const;
 
+    /// @brief Returns a host connected to the IPv4 subnet and having
+    /// a reservation for a specified IPv4 address.
+    ///
+    /// This method returns a single reservation for the particular host
+    /// (identified by the HW address or DUID) as documented in the
+    /// @c BaseHostDataSource::get4.
+    ///
+    /// @param subnet_id Subnet identifier.
+    /// @param address reserved IPv4 address.
+    ///
+    /// @return Const @c Host object using a specified IPv4 address.
+    virtual ConstHostPtr
+    get4(const SubnetID& subnet_id, const asiolink::IOAddress& address) const;
+
     /// @brief Returns a host connected to the IPv6 subnet.
     ///
     /// This method returns a host connected to the IPv6 subnet and identified

src/lib/dhcpsrv/tests/alloc_engine_unittest.cc

@@ -2131,6 +2131,133 @@ TEST_F(AllocEngine4Test, reservedAddressExistingLeaseNoHintFakeAllocation) {
     detailCompareLease(lease, from_mgr);
 }
 
+// This test checks that the behavior of the allocation engine in the following
+// scenario:
+// - Client A has a lease for the address.
+// - Client B has a reservation for the same address that the Client A is using.
+// - Client B requests allocation of the reserved address.
+// - Server returns DHCPNAK to the client to indicate that the requested address
+// can't be allocated.
+// - Client A renews the lease.
+// - Server determines that the lease that the Client A is trying to renews
+// is for the address reserved for Client B. Therefore, the server returns
+// DHCPNAK to force the client to return to the server discovery.
+// - The Client A sends DHCPDISCOVER.
+// - The server offers an address to the Client A, which is different than
+// the address reserved for Client B.
+// - The Client A requests allocation of the offered address.
+// - The server allocates the new address to Client A.
+// - The Client B sends DHCPDISCOVER to the server.
+// - The server offers a reserved address to the Client B.
+// - The Client B requests the offered address.
+// - The server allocates the reserved address to the Client B.
+TEST_F(AllocEngine4Test, reservedAddressConflictResolution) {
+    // Create a reservation for client B.
+    HostPtr host(new Host(&hwaddr2_->hwaddr_[0], hwaddr_->hwaddr_.size(),
+                          Host::IDENT_HWADDR, subnet_->getID(),
+                          SubnetID(0), IOAddress("192.0.2.101")));
+    CfgMgr::instance().getStagingCfg()->getCfgHosts()->add(host);
+    CfgMgr::instance().commit();
+
+    // Create a lease for Client A.
+    Lease4Ptr lease(new Lease4(IOAddress("192.0.2.101"), hwaddr_, 0, 0,
+                               100, 30, 60, time(NULL), subnet_->getID(),
+                               false, false, ""));
+    LeaseMgrFactory::instance().addLease(lease);
+
+    AllocEngine engine(AllocEngine::ALLOC_ITERATIVE, 100, false);
+
+
+    // Client B sends a DHCPREQUEST to allocate a reserved lease. The
+    // allocation engine declines allocation of the address for the
+    // client because Client A has a lease for it.
+    ASSERT_FALSE(engine.allocateLease4(subnet_, ClientIdPtr(), hwaddr2_,
+                                       IOAddress("192.0.2.101"), false,
+                                       false, "", false, CalloutHandlePtr(),
+                                       old_lease_));
+
+    // Client A tries to renew the lease. The renewal should fail because
+    // server detects that Client A doesn't have reservation for this
+    // address.
+    ASSERT_FALSE(engine.allocateLease4(subnet_, clientid_, hwaddr_,
+                                       IOAddress("192.0.2.101"), false, false,
+                                       "", false, CalloutHandlePtr(),
+                                       old_lease_));
+    ASSERT_TRUE(old_lease_);
+    EXPECT_EQ("192.0.2.101", old_lease_->addr_.toText());
+
+    // Client A returns to DHCPDISCOVER and should be offered a lease.
+    // The offered lease address must be different than the one the
+    // Client B has reservation for.
+    Lease4Ptr offered_lease = engine.allocateLease4(subnet_, clientid_,
+                                                    hwaddr_,
+                                                    IOAddress("192.0.2.101"),
+                                                    false, false, "", true,
+                                                    CalloutHandlePtr(),
+                                                    old_lease_);
+    ASSERT_TRUE(offered_lease);
+    EXPECT_NE(offered_lease->addr_.toText(), "192.0.2.101");
+
+    // Client A tried to acquire the lease. It should succeed. At this point
+    // the previous lease should be released and become available for the
+    // Client B.
+    Lease4Ptr allocated_lease = engine.allocateLease4(subnet_, clientid_,
+                                                      hwaddr_,
+                                                      offered_lease->addr_,