dhcp4_srv.cc

// Copyright (C) 2011-2018 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 <kea_version.h>

#include <dhcp/dhcp4.h>
#include <dhcp/duid.h>
#include <dhcp/hwaddr.h>
#include <dhcp/iface_mgr.h>
#include <dhcp/libdhcp++.h>
#include <dhcp/option4_addrlst.h>
#include <dhcp/option_custom.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/pkt4o6.h>
#include <dhcp/pkt6.h>
#include <dhcp/docsis3_option_defs.h>
#include <dhcp4/dhcp4to6_ipc.h>
#include <dhcp4/dhcp4_log.h>
#include <dhcp4/dhcp4_srv.h>
#include <asiolink/addr_utilities.h>
#include <dhcpsrv/cfgmgr.h>
#include <dhcpsrv/cfg_host_operations.h>
#include <dhcpsrv/cfg_iface.h>
#include <dhcpsrv/cfg_shared_networks.h>
#include <dhcpsrv/cfg_subnets4.h>
#include <dhcpsrv/lease_mgr.h>
#include <dhcpsrv/lease_mgr_factory.h>
#include <dhcpsrv/ncr_generator.h>
#include <dhcpsrv/shared_network.h>
#include <dhcpsrv/subnet.h>
#include <dhcpsrv/subnet_selector.h>
#include <dhcpsrv/utils.h>
#include <dhcpsrv/utils.h>
#include <eval/evaluate.h>
#include <eval/eval_messages.h>
#include <hooks/callout_handle.h>
#include <hooks/hooks_log.h>
#include <hooks/hooks_manager.h>
#include <stats/stats_mgr.h>
#include <util/strutil.h>
#include <stats/stats_mgr.h>
#include <log/logger.h>
#include <cryptolink/cryptolink.h>
#include <cfgrpt/config_report.h>

#ifdef HAVE_MYSQL
#include <dhcpsrv/mysql_lease_mgr.h>
#endif
#ifdef HAVE_PGSQL
#include <dhcpsrv/pgsql_lease_mgr.h>
#endif
#ifdef HAVE_CQL
#include <dhcpsrv/cql_lease_mgr.h>
#endif
#include <dhcpsrv/memfile_lease_mgr.h>

#include <boost/algorithm/string/join.hpp>
#include <boost/bind.hpp>
#include <boost/foreach.hpp>
#include <boost/pointer_cast.hpp>
#include <boost/shared_ptr.hpp>

#include <iomanip>

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

namespace {

/// 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_leases4_committed_; ///< index for "leases4_committed" 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
    int hook_index_lease4_decline_;    ///< index for "lease4_decline" hook point
    int hook_index_host4_identifier_;  ///< index for "host4_identifier" 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_leases4_committed_ = HooksManager::registerHook("leases4_committed");
        hook_index_pkt4_send_         = HooksManager::registerHook("pkt4_send");
        hook_index_lease4_release_    = HooksManager::registerHook("lease4_release");
        hook_index_buffer4_send_      = HooksManager::registerHook("buffer4_send");
        hook_index_lease4_decline_    = HooksManager::registerHook("lease4_decline");
        hook_index_host4_identifier_  = HooksManager::registerHook("host4_identifier");
    }
};

} // end of anonymous namespace

// 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();
    // Pointer to client's query.
    context_->query_ = query;

    // If subnet found, retrieve client identifier which will be needed
    // for allocations and search for reservations associated with a
    // subnet/shared network.
    if (subnet) {
        OptionPtr opt_clientid = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
        if (opt_clientid) {
            context_->clientid_.reset(new ClientId(opt_clientid->getData()));
        }

        // Find static reservations if not disabled for our subnet.
        if (subnet->getHostReservationMode() != Network::HR_DISABLED) {
            // Before we can check for static reservations, we need to prepare a set
            // of identifiers to be used for this.
            setHostIdentifiers();

            // Check for static reservations.
            alloc_engine->findReservation(*context_);
        }
    }

    // Set KNOWN builtin class if something was found, UNKNOWN if not.
    if (!context_->hosts_.empty()) {
        query->addClass("KNOWN");
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
            .arg(query->getLabel())
            .arg("KNOWN");
    } else {
        query->addClass("UNKNOWN");
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
            .arg(query->getLabel())
            .arg("UNKNOWN");
    }

    // Perform second pass of classification.
    Dhcpv4Srv::evaluateClasses(query, true);

    const ClientClasses& classes = query_->getClasses();
    if (!classes.empty()) {
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
            .arg(query_->getLabel())
            .arg(classes.toText());
    }
};

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();
        copyDefaultOptions();

        if (getQuery()->isDhcp4o6()) {
            initResponse4o6();
        }
    }
}

void
Dhcpv4Exchange::initResponse4o6() {
    Pkt4o6Ptr query = boost::dynamic_pointer_cast<Pkt4o6>(getQuery());
    if (!query) {
        return;
    }
    const Pkt6Ptr& query6 = query->getPkt6();
    Pkt6Ptr resp6(new Pkt6(DHCPV6_DHCPV4_RESPONSE, query6->getTransid()));
    // Don't add client-id or server-id
    // But copy relay info
    if (!query6->relay_info_.empty()) {
        resp6->copyRelayInfo(query6);
    }
    // Copy interface, and remote address and port
    resp6->setIface(query6->getIface());
    resp6->setIndex(query6->getIndex());
    resp6->setRemoteAddr(query6->getRemoteAddr());
    resp6->setRemotePort(query6->getRemotePort());
    resp_.reset(new Pkt4o6(resp_, resp6));
}

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());

    // 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);
    }

    // Copy flags from the request to the response per RFC 2131
    resp_->setFlags(query_->getFlags());
}

void
Dhcpv4Exchange::copyDefaultOptions() {
    // Let's copy client-id to response. See RFC6842.
    // It is possible to disable RFC6842 to keep backward compatibility
    bool echo = CfgMgr::instance().getCurrentCfg()->getEchoClientId();
    OptionPtr client_id = query_->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (client_id && echo) {
        resp_->addOption(client_id);
    }

    // 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);
    }

    // RFC 3011 states about the Subnet Selection Option

    // "Servers configured to support this option MUST return an
    //  identical copy of the option to any client that sends it,
    //  regardless of whether or not the client requests the option in
    //  a parameter request list. Clients using this option MUST
    //  discard DHCPOFFER or DHCPACK packets that do not contain this
    //  option."
    OptionPtr subnet_sel = query_->getOption(DHO_SUBNET_SELECTION);
    if (subnet_sel) {
        resp_->addOption(subnet_sel);
    }
}

void
Dhcpv4Exchange::setHostIdentifiers() {
    const ConstCfgHostOperationsPtr cfg =
        CfgMgr::instance().getCurrentCfg()->getCfgHostOperations4();

    // Collect host identifiers. The identifiers are stored in order of preference.
    // The server will use them in that order to search for host reservations.
    BOOST_FOREACH(const Host::IdentifierType& id_type,
                  cfg->getIdentifierTypes()) {
        switch (id_type) {
        case Host::IDENT_HWADDR:
            if (context_->hwaddr_ && !context_->hwaddr_->hwaddr_.empty()) {
                context_->addHostIdentifier(id_type, context_->hwaddr_->hwaddr_);
            }
            break;

        case Host::IDENT_DUID:
            if (context_->clientid_) {
                const std::vector<uint8_t>& vec = context_->clientid_->getDuid();
                if (!vec.empty()) {
                    // Client identifier type = DUID? Client identifier holding a DUID
                    // comprises Type (1 byte), IAID (4 bytes), followed by the actual
                    // DUID. Thus, the minimal length is 6.
                    if ((vec[0] == CLIENT_ID_OPTION_TYPE_DUID) && (vec.size() > 5)) {
                        // Extract DUID, skip IAID.
                        context_->addHostIdentifier(id_type,
                                                    std::vector<uint8_t>(vec.begin() + 5,
                                                                         vec.end()));
                    }
                }
            }
            break;

        case Host::IDENT_CIRCUIT_ID:
            {
                OptionPtr rai = query_->getOption(DHO_DHCP_AGENT_OPTIONS);
                if (rai) {
                    OptionPtr circuit_id_opt = rai->getOption(RAI_OPTION_AGENT_CIRCUIT_ID);
                    if (circuit_id_opt) {
                        const OptionBuffer& circuit_id_vec = circuit_id_opt->getData();
                        if (!circuit_id_vec.empty()) {
                            context_->addHostIdentifier(id_type, circuit_id_vec);
                        }
                    }
                }
            }
            break;

        case Host::IDENT_CLIENT_ID:
            if (context_->clientid_) {
                const std::vector<uint8_t>& vec = context_->clientid_->getDuid();
                if (!vec.empty()) {
                    context_->addHostIdentifier(id_type, vec);
                }
            }
            break;
        case Host::IDENT_FLEX:
            {
                if (!HooksManager::calloutsPresent(Hooks.hook_index_host4_identifier_)) {
                    break;
                }

                CalloutHandlePtr callout_handle = getCalloutHandle(context_->query_);

                Host::IdentifierType type = Host::IDENT_FLEX;
                std::vector<uint8_t> id;

                // Use the RAII wrapper to make sure that the callout handle state is
                // reset when this object goes out of scope. All hook points must do
                // it to prevent possible circular dependency between the callout
                // handle and its arguments.
                ScopedCalloutHandleState callout_handle_state(callout_handle);

                // Pass incoming packet as argument
                callout_handle->setArgument("query4", context_->query_);
                callout_handle->setArgument("id_type", type);
                callout_handle->setArgument("id_value", id);

                // Call callouts
                HooksManager::callCallouts(Hooks.hook_index_host4_identifier_,
                                           *callout_handle);

                callout_handle->getArgument("id_type", type);
                callout_handle->getArgument("id_value", id);

                if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_CONTINUE) &&
                    !id.empty()) {

                    LOG_DEBUG(packet4_logger, DBGLVL_TRACE_BASIC, DHCP4_FLEX_ID)
                        .arg(Host::getIdentifierAsText(type, &id[0], id.size()));

                    context_->addHostIdentifier(type, id);
                }
                break;
            }
        default:
            ;
        }
    }
}

void
Dhcpv4Exchange::setReservedClientClasses() {
    if (context_->currentHost() && query_) {
        const ClientClasses& classes = context_->currentHost()->getClientClasses4();
        for (ClientClasses::const_iterator cclass = classes.cbegin();
             cclass != classes.cend(); ++cclass) {
            query_->addClass(*cclass);
        }
    }
}

void
Dhcpv4Exchange::setReservedMessageFields() {
    ConstHostPtr host = context_->currentHost();
    // Nothing to do if host reservations not specified for this client.
    if (host) {
        if (!host->getNextServer().isV4Zero()) {
            resp_->setSiaddr(host->getNextServer());
        }

        std::string sname = host->getServerHostname();
        if (!sname.empty()) {
            resp_->setSname(reinterpret_cast<const uint8_t*>(sname.c_str()),
                            sname.size());
        }

        std::string bootfile = host->getBootFileName();
        if (!bootfile.empty()) {
            resp_->setFile(reinterpret_cast<const uint8_t*>(bootfile.c_str()),
                           bootfile.size());
        }
    }
}

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

Dhcpv4Srv::Dhcpv4Srv(uint16_t port, const bool use_bcast,
                     const bool direct_response_desired)
    : io_service_(new IOService()), shutdown_(true), alloc_engine_(), port_(port),
      use_bcast_(use_bcast), network_state_(new NetworkState(NetworkState::DHCPv4)) {

    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. The number of allocation attempts equal
        // to zero indicates that the allocation engine will use the number of
        // attempts depending on the pool size.
        alloc_engine_.reset(new AllocEngine(AllocEngine::ALLOC_ITERATIVE, 0,
                                            false /* false = IPv4 */));

        /// @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() {
    // Discard any cached packets or parked packets
    discardPackets();

    try {
        stopD2();
    } catch(const std::exception& ex) {
        // Highly unlikely, but lets Report it but go on
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_D2STOP_ERROR).arg(ex.what());
    }

    try {
        Dhcp4to6Ipc::instance().close();
    } catch(const std::exception& ex) {
        // Highly unlikely, but lets Report it but go on
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_DHCP4O6_ERROR).arg(ex.what());
    }

    IfaceMgr::instance().closeSockets();

    // The lease manager was instantiated during DHCPv4Srv configuration,
    // so we should clean up after ourselves.
    LeaseMgrFactory::destroy();

    // Explicitly unload hooks
    HooksManager::getHooksManager().unloadLibraries();
}

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

isc::dhcp::Subnet4Ptr
Dhcpv4Srv::selectSubnet(const Pkt4Ptr& query, bool& drop,
                        bool sanity_only) const {

    // DHCPv4-over-DHCPv6 is a special (and complex) case
    if (query->isDhcp4o6()) {
        return (selectSubnet4o6(query, drop, sanity_only));
    }

    Subnet4Ptr subnet;

    const SubnetSelector& selector = CfgSubnets4::initSelector(query);

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

    // Let's execute all callouts registered for subnet4_select
    // (skip callouts if the selectSubnet was called to do sanity checks only)
    if (!sanity_only &&
        HooksManager::calloutsPresent(Hooks.hook_index_subnet4_select_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

        // 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(Hooks.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->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_SKIP)
                .arg(query->getLabel());
            return (Subnet4Ptr());
        }

        // Callouts decided to drop the packet. It is a superset of the
        // skip case so no subnet will be selected.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_DROP)
                .arg(query->getLabel());
            drop = true;
            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(packet4_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(packet4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_SUBNET_DATA)
            .arg(query->getLabel())
            .arg(subnet->toText());

    } else {
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL,
                  DHCP4_SUBNET_SELECTION_FAILED)
            .arg(query->getLabel());
    }

    return (subnet);
}

isc::dhcp::Subnet4Ptr
Dhcpv4Srv::selectSubnet4o6(const Pkt4Ptr& query, bool& drop,
                           bool sanity_only) const {

    Subnet4Ptr subnet;

    SubnetSelector selector;
    selector.ciaddr_ = query->getCiaddr();
    selector.giaddr_ = query->getGiaddr();
    selector.local_address_ = query->getLocalAddr();
    selector.client_classes_ = query->classes_;
    selector.iface_name_ = query->getIface();
    // Mark it as DHCPv4-over-DHCPv6
    selector.dhcp4o6_ = true;
    // Now the DHCPv6 part
    selector.remote_address_ = query->getRemoteAddr();
    selector.first_relay_linkaddr_ = IOAddress("::");

    // Handle a DHCPv6 relayed query
    Pkt4o6Ptr query4o6 = boost::dynamic_pointer_cast<Pkt4o6>(query);
    if (!query4o6) {
        isc_throw(Unexpected, "Can't get DHCP4o6 message");
    }
    const Pkt6Ptr& query6 = query4o6->getPkt6();

    // Initialize fields specific to relayed messages.
    if (query6 && !query6->relay_info_.empty()) {
        BOOST_REVERSE_FOREACH(Pkt6::RelayInfo relay, query6->relay_info_) {
            if (!relay.linkaddr_.isV6Zero() &&
                !relay.linkaddr_.isV6LinkLocal()) {
                selector.first_relay_linkaddr_ = relay.linkaddr_;
                break;
            }
        }
        selector.interface_id_ =
            query6->getAnyRelayOption(D6O_INTERFACE_ID,
                                      Pkt6::RELAY_GET_FIRST);
    }

    // If the Subnet Selection option is present, extract its value.
    OptionPtr sbnsel = query->getOption(DHO_SUBNET_SELECTION);
    if (sbnsel) {
        OptionCustomPtr oc = boost::dynamic_pointer_cast<OptionCustom>(sbnsel);
        if (oc) {
            selector.option_select_ = oc->readAddress();
        }
    }

    CfgMgr& cfgmgr = CfgMgr::instance();
    subnet = cfgmgr.getCurrentCfg()->getCfgSubnets4()->selectSubnet4o6(selector);

    // Let's execute all callouts registered for subnet4_select.
    // (skip callouts if the selectSubnet was called to do sanity checks only)
    if (!sanity_only &&
        HooksManager::calloutsPresent(Hooks.hook_index_subnet4_select_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // 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(Hooks.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->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_SKIP)
                .arg(query->getLabel());
            return (Subnet4Ptr());
        }

        // Callouts decided to drop the packet. It is a superset of the
        // skip case so no subnet will be selected.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_DROP)
                .arg(query->getLabel());
            drop = true;
            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(packet4_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(packet4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_SUBNET_DATA)
            .arg(query->getLabel())
            .arg(subnet->toText());

    } else {
        LOG_DEBUG(packet4_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_) {
        try {
            run_one();
            getIOService()->poll();
        } catch (const std::exception& e) {
            // General catch-all exception that are not caught by more specific
            // catches. This one is for exceptions derived from std::exception.
            LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_STD_EXCEPTION)
                .arg(e.what());
        } catch (...) {
            // General catch-all exception that are not caught by more specific
            // catches. This one is for other exceptions, not derived from
            // std::exception.
            LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION);
        }
    }

    return (true);
}

void
Dhcpv4Srv::run_one() {
    // client's message and server's response
    Pkt4Ptr query;
    Pkt4Ptr rsp;

    try {
        // Set select() timeout to 1s. This value should not be modified
        // because it is important that the select() returns control
        // frequently so as the IOService can be polled for ready handlers.
        uint32_t timeout = 1;
        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(packet4_logger, DBG_DHCP4_BASIC, DHCP4_BUFFER_RECEIVED)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getRemotePort())
                .arg(query->getLocalAddr().toText())
                .arg(query->getLocalPort())
                .arg(query->getIface());

        }
        // We used to log that the wait was interrupted, but this is no longer
        // the case. Our wait time is 1s now, so the lack of query packet more
        // likely means that nothing new appeared within a second, rather than
        // we were interrupted. And we don't want to print a message every
        // second.

    } 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, SIGHUP or SIGCHLD which are handled by the server. For
        // signals that are not handled by the server we rely on the default
        // behavior of the system.
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_WAIT_SIGNAL)
            .arg(signal_set_->getNext());
    } catch (const std::exception& e) {
        // Log all other errors.
        LOG_ERROR(packet4_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.
    try {
        handleSignal();
    } catch (const std::exception& e) {
        // Standard exception occurred. Let's be on the safe side to
        // catch std::exception.
        LOG_ERROR(dhcp4_logger, DHCP4_HANDLE_SIGNAL_EXCEPTION)
            .arg(e.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) {
        return;
    }

    // If the DHCP service has been globally disabled, drop the packet.
    if (!network_state_->isServiceEnabled()) {
        LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_BASIC,
                  DHCP4_PACKET_DROP_0008)
            .arg(query->getLabel());
        return;
    } else {
        processPacket(query, rsp);
    }

    if (!rsp) {
        return;
    }

    CalloutHandlePtr callout_handle = getCalloutHandle(query);
    processPacketBufferSend(callout_handle, rsp);
}

void
Dhcpv4Srv::processPacket(Pkt4Ptr& query, Pkt4Ptr& rsp, bool allow_packet_park) {
    // 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 statistic further down the road.
    // See processStatsReceived().
    isc::stats::StatsMgr::instance().addValue("pkt4-received",
                                              static_cast<int64_t>(1));

    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);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

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

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

        // Callouts decided to drop the received packet.
        // The response (rsp) is null so the caller (run_one) will
        // immediately return too.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_DETAIL,
                      DHCP4_HOOK_BUFFER_RCVD_DROP)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface());
            return;
        }

        // 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->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            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(options4_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_UNPACK)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface());
            query->unpack();
        } catch (const SkipRemainingOptionsError& e) {
            // An option failed to unpack but we are to attempt to process it
            // anyway.  Log it and let's hope for the best.
            LOG_DEBUG(options4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_PACKET_OPTIONS_SKIPPED)
                .arg(e.what());
        } catch (const std::exception& e) {
            // Failed to parse the packet.
            LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_PACKET_DROP_0001)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface())
                .arg(e.what());

            // Increase the statistics of parse failures and dropped packets.
            isc::stats::StatsMgr::instance().addValue("pkt4-parse-failed",
                                                      static_cast<int64_t>(1));
            isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                      static_cast<int64_t>(1));
            return;
        }
    }

    // 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);

    // Now it is classified the deferred unpacking can be done.
    deferredUnpack(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)) {
        // Increase the statistic of dropped packets.
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
        return;
    }

    // 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(packet4_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(packet4_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(Hooks.hook_index_pkt4_receive_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);