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dhcpd(8)                    System Manager's Manual                   dhcpd(8)

       dhcpd - Dynamic Host Configuration Protocol Server

       dhcpd [ -p port ] [ -f ] [ -d ] [ -q ] [ -t | -T ] [ -4 | -6 ] [ -4o6
       port ] [ -s server ] [ -cf config-file ] [ -lf lease-file ] [ -pf
       pid-file ] [ --no-pid ] [ -user user ] [ -group group ] [ -chroot dir ]
       [ -tf trace-output-file ] [ -play trace-playback-file ] [ if0 [ ...ifN
       ] ]

       dhcpd --version

       The Internet Systems Consortium DHCP Server, dhcpd, implements the
       Dynamic Host Configuration Protocol (DHCP) and the Internet Bootstrap
       Protocol (BOOTP).  DHCP allows hosts on a TCP/IP network to request and
       be assigned IP addresses, and also to discover information about the
       network to which they are attached.  BOOTP provides similar
       functionality, with certain restrictions.

       The DHCP protocol allows a host which is unknown to the network
       administrator to be automatically assigned a new IP address out of a
       pool of IP addresses for its network.  In order for this to work, the
       network administrator allocates address pools in each subnet and enters
       them into the dhcpd.conf(5) file.

       There are two versions of the DHCP protocol DHCPv4 and DHCPv6.  At
       startup the server  may be started for one or the other via the -4 or
       -6 arguments.

       On startup, dhcpd reads the dhcpd.conf file and stores a list of
       available addresses on each subnet in memory.  When a client requests
       an address using the DHCP protocol, dhcpd allocates an address for it.
       Each client is assigned a lease, which expires after an amount of time
       chosen by the administrator (by default, one day).  Before leases
       expire, the clients to which leases are assigned are expected to renew
       them in order to continue to use the addresses.  Once a lease has
       expired, the client to which that lease was assigned is no longer
       permitted to use the leased IP address.

       In order to keep track of leases across system reboots and server
       restarts, dhcpd keeps a list of leases it has assigned in the
       dhcpd.leases(5) file.  Before dhcpd grants a lease to a host, it
       records the lease in this file and makes sure that the contents of the
       file are flushed to disk.  This ensures that even in the event of a
       system crash, dhcpd will not forget about a lease that it has assigned.
       On startup, after reading the dhcpd.conf file, dhcpd reads the
       dhcpd.leases file to refresh its memory about what leases have been

       New leases are appended to the end of the dhcpd.leases file.  In order
       to prevent the file from becoming arbitrarily large, from time to time
       dhcpd creates a new dhcpd.leases file from its in-core lease database.
       Once this file has been written to disk, the old file is renamed
       dhcpd.leases~, and the new file is renamed dhcpd.leases.  If the system
       crashes in the middle of this process, whichever dhcpd.leases file
       remains will contain all the lease information, so there is no need for
       a special crash recovery process.

       BOOTP support is also provided by this server.  Unlike DHCP, the BOOTP
       protocol does not provide a protocol for recovering dynamically-
       assigned addresses once they are no longer needed.  It is still
       possible to dynamically assign addresses to BOOTP clients, but some
       administrative process for reclaiming addresses is required.  By
       default, leases are granted to BOOTP clients in perpetuity, although
       the network administrator may set an earlier cutoff date or a shorter
       lease length for BOOTP leases if that makes sense.

       BOOTP clients may also be served in the old standard way, which is to
       simply provide a declaration in the dhcpd.conf file for each BOOTP
       client, permanently assigning an address to each client.

       Whenever changes are made to the dhcpd.conf file, dhcpd must be
       restarted.  To restart dhcpd, send a SIGTERM (signal 15) to the process
       ID contained in RUNDIR/dhcpd.pid, and then re-invoke dhcpd.  Because
       the DHCP server database is not as lightweight as a BOOTP database,
       dhcpd does not automatically restart itself when it sees a change to
       the dhcpd.conf file.

       Note: We get a lot of complaints about this.  We realize that it would
       be nice if one could send a SIGHUP to the server and have it reload the
       database.  This is not technically impossible, but it would require a
       great deal of work, our resources are extremely limited, and they can
       be better spent elsewhere.  So please don't complain about this on the
       mailing list unless you're prepared to fund a project to implement this
       feature, or prepared to do it yourself.

       The names of the network interfaces on which dhcpd should listen for
       broadcasts may be specified on the command line.  This should be done
       on systems where dhcpd is unable to identify non-broadcast interfaces,
       but should not be required on other systems.  If no interface names are
       specified on the command line dhcpd will identify all network
       interfaces which are up, eliminating non-broadcast interfaces if
       possible, and listen for DHCP broadcasts on each interface.

       -4     Run as a DHCP server. This is the default and cannot be combined
              with -6.

       -6     Run as a DHCPv6 server. This cannot be combined with -4.

       -4o6 port
              Participate in the DHCPv4 over DHCPv6 protocol specified by RFC
              7341.  This associates a DHCPv4 and a DHCPv6 server to allow the
              v4 server to receive v4 requests that were encapsulated in a v6
              packet.  Communication between the two servers is done on a pair
              of UDP sockets bound to ::1 port and port + 1. Both servers must
              be launched using the same port argument.

       -p port
              The UDP port number on which dhcpd should listen.  If
              unspecified dhcpd uses the default port of 67.  This is mostly
              useful for debugging purposes.

       -s address
              Specify an address or host name to which dhcpd should send
              replies rather than the broadcast address (
              This option is only supported in IPv4.

       -f     Force dhcpd to run as a foreground process instead of as a
              daemon in the background.  This is useful when running dhcpd
              under a debugger, or when running it out of inittab on System V

       -d     Send log messages to the standard error descriptor.  This can be
              useful for debugging, and also at sites where a complete log of
              all dhcp activity must be kept but syslogd is not reliable or
              otherwise cannot be used.  Normally, dhcpd will log all output
              using the syslog(3) function with the log facility set to
              LOG_DAEMON.  Note that -d implies -f (the daemon will not fork
              itself into the background).

       -q     Be quiet at startup.  This suppresses the printing of the entire
              copyright message during startup.  This might be desirable when
              starting dhcpd from a system startup script (e.g., /etc/rc).

       -t     Test the configuration file.  The server tests the configuration
              file for correct syntax, but will not attempt to perform any
              network operations.  This can be used to test a new
              configuration file automatically before installing it.

       -T     Test the lease file.  The server tests the lease file for
              correct syntax, but will not attempt to perform any network
              operations.  In addition to reading the lease file it will also
              write the leases to a temporary lease file.  The current lease
              file will not be modified and the temporary lease file will be
              removed upon completion of the test. This can be used to test a
              new lease file automatically before installing it.

       -user user
              Setuid to user after completing privileged operations, such as
              creating sockets that listen on privileged ports.  This also
              causes the lease file to be owned by user.  This option is only
              available if the code was compiled with the PARANOIA patch
              (./configure --enable-paranoia).

       -group group
              Setgid to group after completing privileged operations, such as
              creating sockets that listen on privileged ports.  This also
              causes the lease file to use group.  This option is only
              available if the code was compiled with the PARANOIA patch
              (./configure --enable-paranoia).

       -chroot dir
              Chroot to directory.  This may occur before or after reading the
              configuration files depending on whether the code was compiled
              with the EARLY_CHROOT option enabled (./configure --enable-
              early-chroot).  This option is only available if the code was
              compiled with the PARANOIA patch (./configure --enable-

       -tf tracefile
              Specify a file into which the entire startup state of the server
              and all the transactions it processes are logged.  This can be
              useful in submitting bug reports - if you are getting a core
              dump every so often, you can start the server with the -tf
              option and then, when the server dumps core, the trace file will
              contain all the transactions that led up to it dumping core, so
              that the problem can be easily debugged with -play.

       -play playfile
              Specify a file from which the entire startup state of the server
              and all the transactions it processed are read.  The -play
              option must be specified with an alternate lease file, using the
              -lf switch, so that the DHCP server doesn't wipe out your
              existing lease file with its test data.  The DHCP server will
              refuse to operate in playback mode unless you specify an
              alternate lease file.

              Print version number and exit.

       Modifying default file locations: The following options can be used to
       modify the locations dhcpd uses for its files.  Because of the
       importance of using the same lease database at all times when running
       dhcpd in production, these options should be used only for testing
       lease files or database files in a non-production environment.

       -cf config-file
              Path to alternate configuration file.

       -lf lease-file
              Path to alternate lease file.

       -pf pid-file
              Path to alternate pid file.

              Option to disable writing pid files.  By default the program
              will write a pid file.  If the program is invoked with this
              option it will not check for an existing server process.

       During operations the server may use multiple UDP and TCP ports to
       provide different functions.  Which ports are opened depends on both
       the way you compiled your code and the configuration you supply.  The
       following should provide you an idea of what ports may be in use.

       Normally a DHCPv4 server will open a raw UDP socket to receive and send
       most DHCPv4 packets.  It also opens a fallback UDP socket for use in
       sending unicast packets.  Normally these will both use the well known
       port number for BOOTPS.

       For each DHCPv4 failover peer you list in the configuration file there
       will be a TCP socket listening for connections on the ports specified
       in the configuration file.  When the peer connects there will be
       another socket for the established connection.  For the established
       connection the side (primary or secondary) opening the connection will
       use a random port.

       For DHCPv6 the server opens a UDP socket on the well known
       dhcpv6-server port.

       The server opens an icmp socket for doing ping requests to check if
       addresses are in use.

       If you have included an omapi-port statement in your configuration file
       then the server will open a TCP socket on that port to listen for OMPAI
       connections.  When something connects another port will be used for the
       established connection.

       When DDNS is enabled at compile time (see includes/site.h) the server
       will open both a v4 and a v6 UDP socket on random ports, unless DDNS
       updates are globally disabled by setting ddns-update-style to none in
       the configuration file.

       The syntax of the dhcpd.conf(5) file is discussed separately.  This
       section should be used as an overview of the configuration process, and
       the dhcpd.conf(5) documentation should be consulted for detailed
       reference information.

       dhcpd needs to know the subnet numbers and netmasks of all subnets for
       which it will be providing service.  In addition, in order to
       dynamically allocate addresses, it must be assigned one or more ranges
       of addresses on each subnet which it can in turn assign to client hosts
       as they boot.  Thus, a very simple configuration providing DHCP support
       might look like this:

            subnet netmask {

       Multiple address ranges may be specified like this:

            subnet netmask {

       If a subnet will only be provided with BOOTP service and no dynamic
       address assignment, the range clause can be left out entirely, but the
       subnet statement must appear.

Lease Lengths
       DHCP leases can be assigned almost any length from zero seconds to
       infinity.  What lease length makes sense for any given subnet, or for
       any given installation, will vary depending on the kinds of hosts being

       For example, in an office environment where systems are added from time
       to time and removed from time to time, but move relatively
       infrequently, it might make sense to allow lease times of a month or
       more.  In a final test environment on a manufacturing floor, it may
       make more sense to assign a maximum lease length of 30 minutes - enough
       time to go through a simple test procedure on a network appliance
       before packaging it up for delivery.

       It is possible to specify two lease lengths: the default length that
       will be assigned if a client doesn't ask for any particular lease
       length, and a maximum lease length.  These are specified as clauses to
       the subnet command:

            subnet netmask {
              default-lease-time 600;
              max-lease-time 7200;

       This particular subnet declaration specifies a default lease time of
       600 seconds (ten minutes), and a maximum lease time of 7200 seconds
       (two hours).  Other common values would be 86400 (one day), 604800 (one
       week) and 2592000 (30 days).

       Each subnet need not have the same lease--in the case of an office
       environment and a manufacturing environment served by the same DHCP
       server, it might make sense to have widely disparate values for default
       and maximum lease times on each subnet.

BOOTP Support
       Each BOOTP client must be explicitly declared in the dhcpd.conf file.
       A very basic client declaration will specify the client network
       interface's hardware address and the IP address to assign to that
       client.  If the client needs to be able to load a boot file from the
       server, that file's name must be specified.  A simple bootp client
       declaration might look like this:

            host haagen {
              hardware ethernet 08:00:2b:4c:59:23;
              filename "/tftpboot/haagen.boot";

       DHCP (and also BOOTP with Vendor Extensions) provide a mechanism
       whereby the server can provide the client with information about how to
       configure its network interface (e.g., subnet mask), and also how the
       client can access various network services (e.g., DNS, IP routers, and
       so on).

       These options can be specified on a per-subnet basis, and, for BOOTP
       clients, also on a per-client basis.  In the event that a BOOTP client
       declaration specifies options that are also specified in its subnet
       declaration, the options specified in the client declaration take
       precedence.  A reasonably complete DHCP configuration might look
       something like this:

            subnet netmask {
              default-lease-time 600;
              max-lease-time 7200;
              option subnet-mask;
              option broadcast-address;
              option routers;
              option domain-name-servers,;
              option domain-name "isc.org";

       A bootp host on that subnet that needs to be in a different domain and
       use a different name server might be declared as follows:

            host haagen {
              hardware ethernet 08:00:2b:4c:59:23;
              filename "/tftpboot/haagen.boot";
              option domain-name-servers;
              option domain-name "example.com";

       A more complete description of the dhcpd.conf file syntax is provided
       in dhcpd.conf(5).

       The DHCP server provides the capability to modify some of its
       configuration while it is running, without stopping it, modifying its
       database files, and restarting it.  This capability is currently
       provided using OMAPI - an API for manipulating remote objects.  OMAPI
       clients connect to the server using TCP/IP, authenticate, and can then
       examine the server's current status and make changes to it.

       Rather than implementing the underlying OMAPI protocol directly, user
       programs should use the dhcpctl API or OMAPI itself.  Dhcpctl is a
       wrapper that handles some of the housekeeping chores that OMAPI does
       not do automatically.  Dhcpctl and OMAPI are documented in dhcpctl(3)
       and omapi(3).

       OMAPI exports objects, which can then be examined and modified.  The
       DHCP server exports the following objects: lease, host, failover-state
       and group.  Each object has a number of methods that are provided:
       lookup, create, and destroy.  In addition, it is possible to look at
       attributes that are stored on objects, and in some cases to modify
       those attributes.

       Leases can't currently be created or destroyed, but they can be looked
       up to examine and modify their state.

       Leases have the following attributes:

       state integer lookup, examine
            1 = free
            2 = active
            3 = expired
            4 = released
            5 = abandoned
            6 = reset
            7 = backup
            8 = reserved
            9 = bootp

       ip-address data lookup, examine
            The IP address of the lease.

       dhcp-client-identifier data lookup, examine, update
            The client identifier that the client used when it acquired the
            lease.  Not all clients send client identifiers, so this may be

       client-hostname data examine, update
            The value the client sent in the host-name option.

       host handle examine
            the host declaration associated with this lease, if any.

       subnet handle examine
            the subnet object associated with this lease (the subnet object is
            not currently supported).

       pool handle examine
            the pool object associated with this lease (the pool object is not
            currently supported).

       billing-class handle examine
            the handle to the class to which this lease is currently billed,
            if any (the class object is not currently supported).

       hardware-address data examine, update
            the hardware address (chaddr) field sent by the client when it
            acquired its lease.

       hardware-type integer examine, update
            the type of the network interface that the client reported when it
            acquired its lease.

       ends time examine
            the time when the lease's current state ends, as understood by the

       tstp time examine
            the time when the lease's current state ends, as understood by the
       tsfp time examine
            the adjusted time when the lease's current state ends, as
            understood by the failover peer (if there is no failover peer,
            this value is undefined).  Generally this value is only adjusted
            for expired, released, or reset leases while the server is
            operating in partner-down state, and otherwise is simply the value
            supplied by the peer.
       atsfp time examine
            the actual tsfp value sent from the peer.  This value is forgotten
            when a lease binding state change is made, to facilitate
            retransmission logic.

       cltt time examine
            The time of the last transaction with the client on this lease.

       Hosts can be created, destroyed, looked up, examined and modified.  If
       a host declaration is created or deleted using OMAPI, that information
       will be recorded in the dhcpd.leases file.  It is permissible to delete
       host declarations that are declared in the dhcpd.conf file.

       Hosts have the following attributes:

       name data lookup, examine, modify
            the name of the host declaration.  This name must be unique among
            all host declarations.

       group handle examine, modify
            the named group associated with the host declaration, if there is

       hardware-address data lookup, examine, modify
            the link-layer address that will be used to match the client, if
            any.  Only valid if hardware-type is also present.

       hardware-type integer lookup, examine, modify
            the type of the network interface that will be used to match the
            client, if any.  Only valid if hardware-address is also present.

       dhcp-client-identifier data lookup, examine, modify
            the dhcp-client-identifier option that will be used to match the
            client, if any.

       ip-address data examine, modify
            a fixed IP address which is reserved for a DHCP client that
            matches this host declaration.  The IP address will only be
            assigned to the client if it is valid for the network segment to
            which the client is connected.

       statements data modify
            a list of statements in the format of the dhcpd.conf file that
            will be executed whenever a message from the client is being

       known integer examine, modify
            if nonzero, indicates that a client matching this host declaration
            will be treated as known in pool permit lists.  If zero, the
            client will not be treated as known.

       Named groups can be created, destroyed, looked up, examined and
       modified.  If a group declaration is created or deleted using OMAPI,
       that information will be recorded in the dhcpd.leases file.  It is
       permissible to delete group declarations that are declared in the
       dhcpd.conf file.

       Named groups currently can only be associated with hosts - this allows
       one set of statements to be efficiently attached to more than one host

       Groups have the following attributes:

       name data
            the name of the group.  All groups that are created using OMAPI
            must have names, and the names must be unique among all groups.

       statements data
            a list of statements in the format of the dhcpd.conf file that
            will be executed whenever a message from a client whose host
            declaration references this group is processed.

       The control object allows you to shut the server down.  If the server
       is doing failover with another peer, it will make a clean transition
       into the shutdown state and notify its peer, so that the peer can go
       into partner down, and then record the "recover" state in the lease
       file so that when the server is restarted, it will automatically
       resynchronize with its peer.

       On shutdown the server will also attempt to cleanly shut down all OMAPI
       connections.  If these connections do not go down cleanly after five
       seconds, they are shut down preemptively.  It can take as much as 25
       seconds from the beginning of the shutdown process to the time that the
       server actually exits.

       To shut the server down, open its control object and set the state
       attribute to 2.

       The failover-state object is the object that tracks the state of the
       failover protocol as it is being managed for a given failover peer.
       The failover object has the following attributes (please see dhcpd.conf
       (5) for explanations about what these attributes mean):

       name data examine
            Indicates the name of the failover peer relationship, as described
            in the server's dhcpd.conf file.

       partner-address data examine
            Indicates the failover partner's IP address.

       local-address data examine
            Indicates the IP address that is being used by the DHCP server for
            this failover pair.

       partner-port data examine
            Indicates the TCP port on which the failover partner is listening
            for failover protocol connections.

       local-port data examine
            Indicates the TCP port on which the DHCP server is listening for
            failover protocol connections for this failover pair.

       max-outstanding-updates integer examine
            Indicates the number of updates that can be outstanding and
            unacknowledged at any given time, in this failover relationship.

       mclt integer examine
            Indicates the maximum client lead time in this failover

       load-balance-max-secs integer examine
            Indicates the maximum value for the secs field in a client request
            before load balancing is bypassed.

       load-balance-hba data examine
            Indicates the load balancing hash bucket array for this failover

       local-state integer examine, modify
            Indicates the present state of the DHCP server in this failover
            relationship.  Possible values for state are:

                 1   - startup
                 2   - normal
                 3   - communications interrupted
                 4   - partner down
                 5   - potential conflict
                 6   - recover
                 7   - paused
                 8   - shutdown
                 9   - recover done
                 10  - resolution interrupted
                 11  - conflict done
                 254 - recover wait

            (Note that some of the above values have changed since DHCP

            In general it is not a good idea to make changes to this state.
            However, in the case that the failover partner is known to be
            down, it can be useful to set the DHCP server's failover state to
            partner down.  At this point the DHCP server will take over
            service of the failover partner's leases as soon as possible, and
            will give out normal leases, not leases that are restricted by
            MCLT.  If you do put the DHCP server into the partner-down when
            the other DHCP server is not in the partner-down state, but is not
            reachable, IP address assignment conflicts are possible, even
            likely.  Once a server has been put into partner-down mode, its
            failover partner must not be brought back online until
            communication is possible between the two servers.

       partner-state integer examine
            Indicates the present state of the failover partner.

       local-stos integer examine
            Indicates the time at which the DHCP server entered its present
            state in this failover relationship.

       partner-stos integer examine
            Indicates the time at which the failover partner entered its
            present state.

       hierarchy integer examine
            Indicates whether the DHCP server is primary (0) or secondary (1)
            in this failover relationship.

       last-packet-sent integer examine
            Indicates the time at which the most recent failover packet was
            sent by this DHCP server to its failover partner.

       last-timestamp-received integer examine
            Indicates the timestamp that was on the failover message most
            recently received from the failover partner.

       skew integer examine
            Indicates the skew between the failover partner's clock and this
            DHCP server's clock

       max-response-delay integer examine
            Indicates the time in seconds after which, if no message is
            received from the failover partner, the partner is assumed to be
            out of communication.

       cur-unacked-updates integer examine
            Indicates the number of update messages that have been received
            from the failover partner but not yet processed.

       ETCDIR/dhcpd.conf, DBDIR/dhcpd.leases, RUNDIR/dhcpd.pid,

       dhclient(8), dhcrelay(8), dhcpd.conf(5), dhcpd.leases(5)

       dhcpd(8) was originally written by Ted Lemon under a contract with
       Vixie Labs.  Funding for this project was provided by Internet Systems
       Consortium.  Version 3 of the DHCP server was funded by Nominum, Inc.
       Information about Internet Systems Consortium is available at