dhcp4_srv.cc

// Copyright (C) 2011-2015 Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.

#include <config.h>
#include <asiolink/io_address.h>
#include <dhcp/dhcp4.h>
#include <dhcp/duid.h>
#include <dhcp/hwaddr.h>
#include <dhcp/iface_mgr.h>
#include <dhcp/option4_addrlst.h>
#include <dhcp/option_int.h>
#include <dhcp/option_int_array.h>
#include <dhcp/option_vendor.h>
#include <dhcp/option_string.h>
#include <dhcp/pkt4.h>
#include <dhcp/docsis3_option_defs.h>
#include <dhcp4/dhcp4_log.h>
#include <dhcp4/dhcp4_srv.h>
#include <dhcpsrv/addr_utilities.h>
#include <dhcpsrv/callout_handle_store.h>
#include <dhcpsrv/cfgmgr.h>
#include <dhcpsrv/cfg_subnets4.h>
#include <dhcpsrv/lease_mgr.h>
#include <dhcpsrv/lease_mgr_factory.h>
#include <dhcpsrv/subnet.h>
#include <dhcpsrv/subnet_selector.h>
#include <dhcpsrv/utils.h>
#include <dhcpsrv/utils.h>
#include <hooks/callout_handle.h>
#include <hooks/hooks_log.h>
#include <hooks/hooks_manager.h>
#include <util/strutil.h>
#include <stats/stats_mgr.h>

#include <asio.hpp>
#include <boost/bind.hpp>
#include <boost/foreach.hpp>
#include <boost/shared_ptr.hpp>

#include <iomanip>

using namespace isc;
using namespace isc::asiolink;
using namespace isc::dhcp;
using namespace isc::dhcp_ddns;
using namespace isc::hooks;
using namespace isc::log;
using namespace std;

/// Structure that holds registered hook indexes
struct Dhcp4Hooks {
    int hook_index_buffer4_receive_;///< index for "buffer4_receive" hook point
    int hook_index_pkt4_receive_;   ///< index for "pkt4_receive" hook point
    int hook_index_subnet4_select_; ///< index for "subnet4_select" hook point
    int hook_index_lease4_release_; ///< index for "lease4_release" hook point
    int hook_index_pkt4_send_;      ///< index for "pkt4_send" hook point
    int hook_index_buffer4_send_;   ///< index for "buffer4_send" hook point

    /// Constructor that registers hook points for DHCPv4 engine
    Dhcp4Hooks() {
        hook_index_buffer4_receive_= HooksManager::registerHook("buffer4_receive");
        hook_index_pkt4_receive_   = HooksManager::registerHook("pkt4_receive");
        hook_index_subnet4_select_ = HooksManager::registerHook("subnet4_select");
        hook_index_pkt4_send_      = HooksManager::registerHook("pkt4_send");
        hook_index_lease4_release_ = HooksManager::registerHook("lease4_release");
        hook_index_buffer4_send_   = HooksManager::registerHook("buffer4_send");
    }
};

// Declare a Hooks object. As this is outside any function or method, it
// will be instantiated (and the constructor run) when the module is loaded.
// As a result, the hook indexes will be defined before any method in this
// module is called.
Dhcp4Hooks Hooks;

namespace isc {
namespace dhcp {

Dhcpv4Exchange::Dhcpv4Exchange(const AllocEnginePtr& alloc_engine,
                               const Pkt4Ptr& query,
                               const Subnet4Ptr& subnet)
    : alloc_engine_(alloc_engine), query_(query), resp_(),
      context_(new AllocEngine::ClientContext4()) {

    if (!alloc_engine_) {
        isc_throw(BadValue, "alloc_engine value must not be NULL"
                  " when creating an instance of the Dhcpv4Exchange");
    }

    if (!query_) {
        isc_throw(BadValue, "query value must not be NULL when"
                  " creating an instance of the Dhcpv4Exchange");
    }

    // Create response message.
    initResponse();
    // Select subnet for the query message.
    context_->subnet_ = subnet;
    // Hardware address.
    context_->hwaddr_ = query->getHWAddr();
    // Client Identifier
    OptionPtr opt_clientid = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (opt_clientid) {
        context_->clientid_.reset(new ClientId(opt_clientid->getData()));
    }
    // Check for static reservations.
    alloc_engine->findReservation(*context_);
};

void
Dhcpv4Exchange::initResponse() {
    uint8_t resp_type = 0;
    switch (getQuery()->getType()) {
    case DHCPDISCOVER:
        resp_type = DHCPOFFER;
        break;
    case DHCPREQUEST:
    case DHCPINFORM:
        resp_type = DHCPACK;
        break;
    default:
        ;
    }
    // Only create a response if one is required.
    if (resp_type > 0) {
        resp_.reset(new Pkt4(resp_type, getQuery()->getTransid()));
        copyDefaultFields();
    }
}

void
Dhcpv4Exchange::copyDefaultFields() {
    resp_->setIface(query_->getIface());
    resp_->setIndex(query_->getIndex());

    // explicitly set this to 0
    resp_->setSiaddr(IOAddress::IPV4_ZERO_ADDRESS());
    // ciaddr is always 0, except for the Renew/Rebind state when it may
    // be set to the ciaddr sent by the client.
    resp_->setCiaddr(IOAddress::IPV4_ZERO_ADDRESS());
    resp_->setHops(query_->getHops());

    // copy MAC address
    resp_->setHWAddr(query_->getHWAddr());

    // relay address
    resp_->setGiaddr(query_->getGiaddr());

    // Let's copy client-id to response. See RFC6842.
    // It is possible to disable RFC6842 to keep backward compatibility
    bool echo = CfgMgr::instance().echoClientId();
    OptionPtr client_id = query_->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (client_id && echo) {
        resp_->addOption(client_id);
    }

    // If src/dest HW addresses are used by the packet filtering class
    // we need to copy them as well. There is a need to check that the
    // address being set is not-NULL because an attempt to set the NULL
    // HW would result in exception. If these values are not set, the
    // the default HW addresses (zeroed) should be generated by the
    // packet filtering class when creating Ethernet header for
    // outgoing packet.
    HWAddrPtr src_hw_addr = query_->getLocalHWAddr();
    if (src_hw_addr) {
        resp_->setLocalHWAddr(src_hw_addr);
    }
    HWAddrPtr dst_hw_addr = query_->getRemoteHWAddr();
    if (dst_hw_addr) {
        resp_->setRemoteHWAddr(dst_hw_addr);
    }

    // If this packet is relayed, we want to copy Relay Agent Info option
    OptionPtr rai = query_->getOption(DHO_DHCP_AGENT_OPTIONS);
    if (rai) {
        resp_->addOption(rai);
    }
}

const std::string Dhcpv4Srv::VENDOR_CLASS_PREFIX("VENDOR_CLASS_");

Dhcpv4Srv::Dhcpv4Srv(uint16_t port, const bool use_bcast,
                     const bool direct_response_desired)
    : shutdown_(true), alloc_engine_(), port_(port),
      use_bcast_(use_bcast), hook_index_pkt4_receive_(-1),
      hook_index_subnet4_select_(-1), hook_index_pkt4_send_(-1) {

    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_START, DHCP4_OPEN_SOCKET).arg(port);
    try {
        // Port 0 is used for testing purposes where we don't open broadcast
        // capable sockets. So, set the packet filter handling direct traffic
        // only if we are in non-test mode.
        if (port) {
            // First call to instance() will create IfaceMgr (it's a singleton)
            // it may throw something if things go wrong.
            // The 'true' value of the call to setMatchingPacketFilter imposes
            // that IfaceMgr will try to use the mechanism to respond directly
            // to the client which doesn't have address assigned. This capability
            // may be lacking on some OSes, so there is no guarantee that server
            // will be able to respond directly.
            IfaceMgr::instance().setMatchingPacketFilter(direct_response_desired);
        }

        // Instantiate allocation engine
        alloc_engine_.reset(new AllocEngine(AllocEngine::ALLOC_ITERATIVE, 100,
                                            false /* false = IPv4 */));

        // Register hook points
        hook_index_pkt4_receive_   = Hooks.hook_index_pkt4_receive_;
        hook_index_subnet4_select_ = Hooks.hook_index_subnet4_select_;
        hook_index_pkt4_send_      = Hooks.hook_index_pkt4_send_;

        /// @todo call loadLibraries() when handling configuration changes

    } catch (const std::exception &e) {
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_CONSTRUCT_ERROR).arg(e.what());
        shutdown_ = true;
        return;
    }

    shutdown_ = false;
}

Dhcpv4Srv::~Dhcpv4Srv() {
    IfaceMgr::instance().closeSockets();
}

void
Dhcpv4Srv::shutdown() {
    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_SHUTDOWN_REQUEST);
    shutdown_ = true;
}

isc::dhcp::Subnet4Ptr
Dhcpv4Srv::selectSubnet(const Pkt4Ptr& query) const {

    Subnet4Ptr subnet;

    SubnetSelector selector;
    selector.ciaddr_ = query->getCiaddr();
    selector.giaddr_ = query->getGiaddr();
    selector.local_address_ = query->getLocalAddr();
    selector.remote_address_ = query->getRemoteAddr();
    selector.client_classes_ = query->classes_;
    selector.iface_name_ = query->getIface();

    CfgMgr& cfgmgr = CfgMgr::instance();
    subnet = cfgmgr.getCurrentCfg()->getCfgSubnets4()->selectSubnet(selector);

    // Let's execute all callouts registered for subnet4_select
    if (HooksManager::calloutsPresent(hook_index_subnet4_select_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // We're reusing callout_handle from previous calls
        callout_handle->deleteAllArguments();

        // Set new arguments
        callout_handle->setArgument("query4", query);
        callout_handle->setArgument("subnet4", subnet);
        callout_handle->setArgument("subnet4collection",
                                    cfgmgr.getCurrentCfg()->
                                    getCfgSubnets4()->getAll());

        // Call user (and server-side) callouts
        HooksManager::callCallouts(hook_index_subnet4_select_,
                                   *callout_handle);

        // Callouts decided to skip this step. This means that no subnet
        // will be selected. Packet processing will continue, but it will
        // be severely limited (i.e. only global options will be assigned)
        if (callout_handle->getSkip()) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_SKIP)
                .arg(query->getLabel());
            return (Subnet4Ptr());
        }

        // Use whatever subnet was specified by the callout
        callout_handle->getArgument("subnet4", subnet);
    }

    if (subnet) {
        // Log at higher debug level that subnet has been found.
        LOG_DEBUG(packet_logger, DBG_DHCP4_BASIC_DATA, DHCP4_SUBNET_SELECTED)
            .arg(query->getLabel())
            .arg(subnet->getID());
        // Log detailed information about the selected subnet at the
        // lower debug level.
        LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_SUBNET_DATA)
            .arg(query->getLabel())
            .arg(subnet->toText());

    } else {
        LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL,
                  DHCP4_SUBNET_SELECTION_FAILED)
            .arg(query->getLabel());
    }

    return (subnet);
}

Pkt4Ptr
Dhcpv4Srv::receivePacket(int timeout) {
    return (IfaceMgr::instance().receive4(timeout));
}

void
Dhcpv4Srv::sendPacket(const Pkt4Ptr& packet) {
    IfaceMgr::instance().send(packet);
}

bool
Dhcpv4Srv::run() {
    while (!shutdown_) {
        // client's message and server's response
        Pkt4Ptr query;
        Pkt4Ptr rsp;

        try {
            // The lease database backend may install some timers for which
            // the handlers need to be executed periodically. Retrieve the
            // maximum interval at which the handlers must be executed from
            // the lease manager.
            uint32_t timeout = LeaseMgrFactory::instance().getIOServiceExecInterval();
            // If the returned value is zero it means that there are no
            // timers installed, so use a default value.
            if (timeout == 0) {
                timeout = 1000;
            }
            LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_WAIT).arg(timeout);
            query = receivePacket(timeout);

            // Log if packet has arrived. We can't log the detailed information
            // about the DHCP message because it hasn't been unpacked/parsed
            // yet, and it can't be parsed at this point because hooks will
            // have to process it first. The only information available at this
            // point are: the interface, source address and destination addresses
            // and ports.
            if (query) {
                LOG_DEBUG(packet_logger, DBG_DHCP4_BASIC, DHCP4_BUFFER_RECEIVED)
                    .arg(query->getRemoteAddr().toText())
                    .arg(query->getRemotePort())
                    .arg(query->getLocalAddr().toText())
                    .arg(query->getLocalPort())
                    .arg(query->getIface());

            } else {
                LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_WAIT_TIMEOUT)
                    .arg(timeout);
            }

        } catch (const SignalInterruptOnSelect) {
            // Packet reception interrupted because a signal has been received.
            // This is not an error because we might have received a SIGTERM,
            // SIGINT or SIGHUP which are handled by the server. For signals
            // that are not handled by the server we rely on the default
            // behavior of the system, but there is nothing we should log here.
            LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_WAIT_SIGNAL)
                .arg(signal_set_->getNext());
        } catch (const std::exception& e) {
            // Log all other errors.
            LOG_ERROR(packet_logger, DHCP4_BUFFER_RECEIVE_FAIL).arg(e.what());
        }

        // Handle next signal received by the process. It must be called after
        // an attempt to receive a packet to properly handle server shut down.
        // The SIGTERM or SIGINT will be received prior to, or during execution
        // of select() (select is invoked by receivePacket()). When that
        // happens, select will be interrupted. The signal handler will be
        // invoked immediately after select(). The handler will set the
        // shutdown flag and cause the process to terminate before the next
        // select() function is called. If the function was called before
        // receivePacket the process could wait up to the duration of timeout
        // of select() to terminate.
        handleSignal();

        // Execute ready timers for the lease database, e.g. Lease File Cleanup.
        try {
            LeaseMgrFactory::instance().getIOService()->poll();

        } catch (const std::exception& ex) {
            LOG_WARN(dhcp4_logger, DHCP4_LEASE_DATABASE_TIMERS_EXEC_FAIL)
                .arg(ex.what());
        }

        // Timeout may be reached or signal received, which breaks select()
        // with no reception occurred. No need to log anything here because
        // we have logged right after the call to receivePacket().
        if (!query) {
            continue;
        }

        // Log reception of the packet. We need to increase it early, as any
        // failures in unpacking will cause the packet to be dropped. We
        // will increase type specific packets further down the road.
        // See processStatsReceived().
        isc::stats::StatsMgr::instance().addValue("pkt4-received", 1ul);

        // In order to parse the DHCP options, the server needs to use some
        // configuration information such as: existing option spaces, option
        // definitions etc. This is the kind of information which is not
        // available in the libdhcp, so we need to supply our own implementation
        // of the option parsing function here, which would rely on the
        // configuration data.
        query->setCallback(boost::bind(&Dhcpv4Srv::unpackOptions, this,
                                       _1, _2, _3));

        bool skip_unpack = false;

        // The packet has just been received so contains the uninterpreted wire
        // data; execute callouts registered for buffer4_receive.
        if (HooksManager::calloutsPresent(Hooks.hook_index_buffer4_receive_)) {
            CalloutHandlePtr callout_handle = getCalloutHandle(query);

            // Delete previously set arguments
            callout_handle->deleteAllArguments();

            // Pass incoming packet as argument
            callout_handle->setArgument("query4", query);

            // Call callouts
            HooksManager::callCallouts(Hooks.hook_index_buffer4_receive_,
                                       *callout_handle);

            // Callouts decided to skip the next processing step. The next
            // processing step would to parse the packet, so skip at this
            // stage means that callouts did the parsing already, so server
            // should skip parsing.
            if (callout_handle->getSkip()) {
                LOG_DEBUG(hooks_logger, DBG_DHCP4_DETAIL, DHCP4_HOOK_BUFFER_RCVD_SKIP)
                    .arg(query->getRemoteAddr().toText())
                    .arg(query->getLocalAddr().toText())
                    .arg(query->getIface());
                skip_unpack = true;
            }

            callout_handle->getArgument("query4", query);
        }

        // Unpack the packet information unless the buffer4_receive callouts
        // indicated they did it
        if (!skip_unpack) {
            try {
                LOG_DEBUG(options_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_UNPACK)
                    .arg(query->getRemoteAddr().toText())
                    .arg(query->getLocalAddr().toText())
                    .arg(query->getIface());
                query->unpack();
            } catch (const std::exception& e) {
                // Failed to parse the packet.
                LOG_DEBUG(bad_packet_logger, DBG_DHCP4_DETAIL,
                          DHCP4_PACKET_DROP_0001)
                    .arg(query->getRemoteAddr().toText())
                    .arg(query->getLocalAddr().toText())
                    .arg(query->getIface())
                    .arg(e.what());
                continue;
            }
        }

        // Update statistics accordingly for received packet.
        processStatsReceived(query);

        // Assign this packet to one or more classes if needed. We need to do
        // this before calling accept(), because getSubnet4() may need client
        // class information.
        classifyPacket(query);

        // Check whether the message should be further processed or discarded.
        // There is no need to log anything here. This function logs by itself.
        if (!accept(query)) {
            isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop", 1ul);
            continue;
        }

        // We have sanity checked (in accept() that the Message Type option
        // exists, so we can safely get it here.
        int type = query->getType();
        LOG_DEBUG(packet_logger, DBG_DHCP4_BASIC_DATA, DHCP4_PACKET_RECEIVED)
            .arg(query->getLabel())
            .arg(query->getName())
            .arg(type)
            .arg(query->getRemoteAddr())
            .arg(query->getLocalAddr())
            .arg(query->getIface());
        LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_QUERY_DATA)
            .arg(query->getLabel())
            .arg(query->toText());

        // Let's execute all callouts registered for pkt4_receive
        if (HooksManager::calloutsPresent(hook_index_pkt4_receive_)) {
            CalloutHandlePtr callout_handle = getCalloutHandle(query);

            // Delete previously set arguments
            callout_handle->deleteAllArguments();

            // Pass incoming packet as argument
            callout_handle->setArgument("query4", query);

            // Call callouts
            HooksManager::callCallouts(hook_index_pkt4_receive_,
                                       *callout_handle);

            // Callouts decided to skip the next processing step. The next
            // processing step would to process the packet, so skip at this
            // stage means drop.
            if (callout_handle->getSkip()) {
                LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_RCVD_SKIP)
                    .arg(query->getLabel());
                continue;
            }

            callout_handle->getArgument("query4", query);
        }

        try {
            switch (query->getType()) {
            case DHCPDISCOVER:
                rsp = processDiscover(query);
                break;

            case DHCPREQUEST:
                // Note that REQUEST is used for many things in DHCPv4: for
                // requesting new leases, renewing existing ones and even
                // for rebinding.
                rsp = processRequest(query);
                break;

            case DHCPRELEASE:
                processRelease(query);
                break;

            case DHCPDECLINE:
                processDecline(query);
                break;

            case DHCPINFORM:
                rsp = processInform(query);
                break;

            default:
                // Only action is to output a message if debug is enabled,
                // and that is covered by the debug statement before the
                // "switch" statement.
                ;
            }
        } catch (const isc::Exception& e) {

            // Catch-all exception (at least for ones based on the isc Exception
            // class, which covers more or less all that are explicitly raised
            // in the Kea code).  Just log the problem and ignore the packet.
            // (The problem is logged as a debug message because debug is
            // disabled by default - it prevents a DDOS attack based on the
            // sending of problem packets.)
            LOG_DEBUG(bad_packet_logger, DBG_DHCP4_BASIC,
                      DHCP4_PACKET_DROP_0007)
                .arg(query->getLabel())
                .arg(e.what());
        }

        if (!rsp) {
            continue;
        }


        // Specifies if server should do the packing
        bool skip_pack = false;

        // Execute all callouts registered for pkt4_send
        if (HooksManager::calloutsPresent(hook_index_pkt4_send_)) {
            CalloutHandlePtr callout_handle = getCalloutHandle(query);

            // Delete all previous arguments
            callout_handle->deleteAllArguments();

            // Clear skip flag if it was set in previous callouts
            callout_handle->setSkip(false);

            // Set our response
            callout_handle->setArgument("response4", rsp);

            // Call all installed callouts
            HooksManager::callCallouts(hook_index_pkt4_send_,
                                       *callout_handle);

            // Callouts decided to skip the next processing step. The next
            // processing step would to send the packet, so skip at this
            // stage means "drop response".
            if (callout_handle->getSkip()) {
                LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_SEND_SKIP)
                    .arg(query->getLabel());
                skip_pack = true;
            }
        }

        if (!skip_pack) {
            try {
                LOG_DEBUG(options_logger, DBG_DHCP4_DETAIL, DHCP4_PACKET_PACK)
                    .arg(rsp->getLabel());
                rsp->pack();
            } catch (const std::exception& e) {
                LOG_ERROR(options_logger, DHCP4_PACKET_PACK_FAIL)
                    .arg(rsp->getLabel())
                    .arg(e.what());
            }
        }

        try {
            // Now all fields and options are constructed into output wire buffer.
            // Option objects modification does not make sense anymore. Hooks
            // can only manipulate wire buffer at this stage.
            // Let's execute all callouts registered for buffer4_send
            if (HooksManager::calloutsPresent(Hooks.hook_index_buffer4_send_)) {
                CalloutHandlePtr callout_handle = getCalloutHandle(query);

                // Delete previously set arguments
                callout_handle->deleteAllArguments();

                // Pass incoming packet as argument
                callout_handle->setArgument("response4", rsp);

                // Call callouts
                HooksManager::callCallouts(Hooks.hook_index_buffer4_send_,
                                           *callout_handle);

                // Callouts decided to skip the next processing step. The next
                // processing step would to parse the packet, so skip at this
                // stage means drop.
                if (callout_handle->getSkip()) {
                    LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                              DHCP4_HOOK_BUFFER_SEND_SKIP)
                        .arg(rsp->getLabel());
                    continue;
                }

                callout_handle->getArgument("response4", rsp);
            }

            LOG_DEBUG(packet_logger, DBG_DHCP4_BASIC, DHCP4_PACKET_SEND)
                .arg(rsp->getLabel())
                .arg(rsp->getName())
                .arg(static_cast<int>(rsp->getType()))
                .arg(rsp->getLocalAddr())
                .arg(rsp->getLocalPort())
                .arg(rsp->getRemoteAddr())
                .arg(rsp->getRemotePort())
                .arg(rsp->getIface());

            LOG_DEBUG(packet_logger, DBG_DHCP4_DETAIL_DATA,
                      DHCP4_RESPONSE_DATA)
                .arg(rsp->getLabel())
                .arg(rsp->getName())
                .arg(static_cast<int>(rsp->getType()))
                .arg(rsp->toText());
            sendPacket(rsp);

            // Update statistics accordingly for sent packet.
            processStatsSent(rsp);

        } catch (const std::exception& e) {
            LOG_ERROR(packet_logger, DHCP4_PACKET_SEND_FAIL)
                .arg(rsp->getLabel())
                .arg(e.what());
        }
    }

    return (true);
}

string
Dhcpv4Srv::srvidToString(const OptionPtr& srvid) {
    if (!srvid) {
        isc_throw(BadValue, "NULL pointer passed to srvidToString()");
    }
    boost::shared_ptr<Option4AddrLst> generated =
        boost::dynamic_pointer_cast<Option4AddrLst>(srvid);
    if (!srvid) {
        isc_throw(BadValue, "Pointer to invalid option passed to srvidToString()");
    }

    Option4AddrLst::AddressContainer addrs = generated->getAddresses();
    if (addrs.size() != 1) {
        isc_throw(BadValue, "Malformed option passed to srvidToString(). "
                  << "Expected to contain a single IPv4 address.");
    }

    return (addrs[0].toText());
}

isc::dhcp_ddns::D2Dhcid
Dhcpv4Srv::computeDhcid(const Lease4Ptr& lease) {
    if (!lease) {
        isc_throw(DhcidComputeError, "a pointer to the lease must be not"
                  " NULL to compute DHCID");

    } else if (lease->hostname_.empty()) {
        isc_throw(DhcidComputeError, "unable to compute the DHCID for the"
                  " lease which has empty hostname set");

    }

    // In order to compute DHCID the client's hostname must be encoded in
    // canonical wire format. It is unlikely that the FQDN is malformed
    // because it is validated by the classes which encapsulate options
    // carrying client FQDN. However, if the client name was carried in the
    // Hostname option it is more likely as it carries the hostname as a
    // regular string.
    std::vector<uint8_t> fqdn_wire;
    try {
        OptionDataTypeUtil::writeFqdn(lease->hostname_, fqdn_wire, true);

    } catch (const Exception& ex) {
        isc_throw(DhcidComputeError, "unable to compute DHCID because the"
                  " hostname: " << lease->hostname_ << " is invalid");

    }

    // Prefer client id to HW address to compute DHCID. If Client Id is
    // NULL, use HW address.
    try {
        if (lease->client_id_) {
            return (D2Dhcid(lease->client_id_->getClientId(), fqdn_wire));

        } else {
            return (D2Dhcid(lease->hwaddr_, fqdn_wire));
        }
    } catch (const Exception& ex) {
        isc_throw(DhcidComputeError, "unable to compute DHCID: "
                  << ex.what());

    }

}

void
Dhcpv4Srv::appendServerID(Dhcpv4Exchange& ex) {
    // The source address for the outbound message should have been set already.
    // This is the address that to the best of the server's knowledge will be
    // available from the client.
    /// @todo: perhaps we should consider some more sophisticated server id
    /// generation, but for the current use cases, it should be ok.
    OptionPtr opt_srvid(new Option4AddrLst(DHO_DHCP_SERVER_IDENTIFIER,
                                           ex.getResponse()->getLocalAddr()));
    ex.getResponse()->addOption(opt_srvid);
}

void
Dhcpv4Srv::appendRequestedOptions(Dhcpv4Exchange& ex) {
    // Get the subnet relevant for the client. We will need it
    // to get the options associated with it.
    Subnet4Ptr subnet = ex.getContext()->subnet_;
    // If we can't find the subnet for the client there is no way
    // to get the options to be sent to a client. We don't log an
    // error because it will be logged by the assignLease method
    // anyway.
    if (!subnet) {
        return;
    }

    Pkt4Ptr query = ex.getQuery();

    // try to get the 'Parameter Request List' option which holds the
    // codes of requested options.
    OptionUint8ArrayPtr option_prl = boost::dynamic_pointer_cast<
        OptionUint8Array>(query->getOption(DHO_DHCP_PARAMETER_REQUEST_LIST));
    // If there is no PRL option in the message from the client then
    // there is nothing to do.
    if (!option_prl) {
        return;
    }

    Pkt4Ptr resp = ex.getResponse();

    // Get the codes of requested options.
    const std::vector<uint8_t>& requested_opts = option_prl->getValues();
    // For each requested option code get the instance of the option
    // to be returned to the client.
    for (std::vector<uint8_t>::const_iterator opt = requested_opts.begin();
         opt != requested_opts.end(); ++opt) {
        if (!resp->getOption(*opt)) {
            OptionDescriptor desc = subnet->getCfgOption()->get("dhcp4", *opt);
            if (desc.option_) {
                resp->addOption(desc.option_);
            }
        }
    }
}

void
Dhcpv4Srv::appendRequestedVendorOptions(Dhcpv4Exchange& ex) {
    // Get the configured subnet suitable for the incoming packet.
    Subnet4Ptr subnet = ex.getContext()->subnet_;
    // Leave if there is no subnet matching the incoming packet.
    // There is no need to log the error message here because
    // it will be logged in the assignLease() when it fails to
    // pick the suitable subnet. We don't want to duplicate
    // error messages in such case.
    if (!subnet) {
        return;
    }

    // Try to get the vendor option
    boost::shared_ptr<OptionVendor> vendor_req = boost::dynamic_pointer_cast<
        OptionVendor>(ex.getQuery()->getOption(DHO_VIVSO_SUBOPTIONS));
    if (!vendor_req) {
        return;
    }

    uint32_t vendor_id = vendor_req->getVendorId();

    // Let's try to get ORO within that vendor-option
    /// @todo This is very specific to vendor-id=4491 (Cable Labs). Other
    /// vendors may have different policies.
    OptionUint8ArrayPtr oro =
        boost::dynamic_pointer_cast<OptionUint8Array>(vendor_req->getOption(DOCSIS3_V4_ORO));

    // Option ORO not found. Don't do anything then.
    if (!oro) {
        return;
    }

    boost::shared_ptr<OptionVendor> vendor_rsp(new OptionVendor(Option::V4, vendor_id));

    // Get the list of options that client requested.
    bool added = false;
    const std::vector<uint8_t>& requested_opts = oro->getValues();

    for (std::vector<uint8_t>::const_iterator code = requested_opts.begin();
         code != requested_opts.end(); ++code) {
        if  (!vendor_rsp->getOption(*code)) {
            OptionDescriptor desc = subnet->getCfgOption()->get(vendor_id,
                                                                *code);
            if (desc.option_) {
                vendor_rsp->addOption(desc.option_);
                added = true;
            }
        }

        if (added) {
            ex.getResponse()->addOption(vendor_rsp);
        }
    }
}


void
Dhcpv4Srv::appendBasicOptions(Dhcpv4Exchange& ex) {
    // Identify options that we always want to send to the
    // client (if they are configured).
    static const uint16_t required_options[] = {
        DHO_ROUTERS,
        DHO_DOMAIN_NAME_SERVERS,
        DHO_DOMAIN_NAME };

    static size_t required_options_size =
        sizeof(required_options) / sizeof(required_options[0]);

    // Get the subnet.
    Subnet4Ptr subnet = ex.getContext()->subnet_;
    if (!subnet) {
        return;
    }

    Pkt4Ptr resp = ex.getResponse();

    // Try to find all 'required' options in the outgoing
    // message. Those that are not present will be added.
    for (int i = 0; i < required_options_size; ++i) {
        OptionPtr opt = resp->getOption(required_options[i]);
        if (!opt) {
            // Check whether option has been configured.
            OptionDescriptor desc = subnet->getCfgOption()->
                get("dhcp4", required_options[i]);
            if (desc.option_) {
                resp->addOption(desc.option_);
            }
        }
    }
}

void
Dhcpv4Srv::processClientName(Dhcpv4Exchange& ex) {
    // It is possible that client has sent both Client FQDN and Hostname
    // option. In such case, server should prefer Client FQDN option and
    // ignore the Hostname option.
    try {
        Pkt4Ptr resp = ex.getResponse();
        Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<Option4ClientFqdn>
            (ex.getQuery()->getOption(DHO_FQDN));
        if (fqdn) {
            LOG_DEBUG(ddns_logger, DBG_DHCP4_DETAIL, DHCP4_CLIENT_FQDN_PROCESS)
                .arg(ex.getQuery()->getLabel());
            processClientFqdnOption(ex);

        } else {
            OptionStringPtr hostname = boost::dynamic_pointer_cast<OptionString>
                (ex.getQuery()->getOption(DHO_HOST_NAME));
            if (hostname) {
                LOG_DEBUG(ddns_logger, DBG_DHCP4_DETAIL, DHCP4_CLIENT_HOSTNAME_PROCESS)
                    .arg(ex.getQuery()->getLabel());
                processHostnameOption(ex);
            }
        }
    } catch (const Exception& e) {
        // In some rare cases it is possible that the client's name processing
        // fails. For example, the Hostname option may be malformed, or there
        // may be an error in the server's logic which would cause multiple
        // attempts to add the same option to the response message. This
        // error message aggregates all these errors so they can be diagnosed
        // from the log. We don't want to throw an exception here because,
        // it will impact the processing of the whole packet. We rather want
        // the processing to continue, even if the client's name is wrong.
        LOG_DEBUG(ddns_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_CLIENT_NAME_PROC_FAIL)
            .arg(ex.getQuery()->getLabel())
            .arg(e.what());
    }
}

void
Dhcpv4Srv::processClientFqdnOption(Dhcpv4Exchange& ex) {