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

       dhcpd - Dynamic Host Configuration Protocol Server

       dhcpd [ -p port ] [ -f ] [ -d ] [ -q ] [ -t | -T ] [ -cf config-file ]
       [ -lf lease-file ] [ -pf pid-file ] [ -tf trace-output-file ] [ -play
       trace-playback-file ] [ if0 [ ...ifN ] ]

       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.

       This software is free software.  At various times its development has
       been underwritten by various organizations, including the ISC and Vixie
       Enterprises.  The development of 3.0 has been funded almost entirely by
       Nominum, Inc.

       At this point development is being shepherded by Ted Lemon, and hosted
       by the ISC, but the future of this project depends on you.  If you have
       features you want, please consider implementing them.

       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.

       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 /var/run/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.

       If dhcpd should listen on a port other than the standard (port 67), the
       -p flag may used.  It should be followed by the udp port number on
       which dhcpd should listen.  This is mostly useful for debugging

       To run dhcpd as a foreground process, rather than allowing it to run as
       a daemon in the background, the -f flag should be specified.  This is
       useful when running dhcpd under a debugger, or when running it out of
       inittab on System V systems.

       To have dhcpd log to the standard error descriptor, specify the -d
       flag.  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).

       Dhcpd can be made to use an alternate configuration file with the -cf
       flag, an alternate lease file with the -lf flag, or an alternate pid
       file with the -pf flag.   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.

       When starting dhcpd up from a system startup script (e.g., /etc/rc), it
       may not be desirable to print out the entire copyright message on
       startup.   To avoid printing this message, the -q flag may be

       The DHCP server reads two files on startup: a configuration file, and a
       lease database.   If the -t flag is specified, the server will simply
       test the configuration file for correct syntax, but will not attempt to
       perform any network operations.   This can be used to test the a new
       configuration file automatically before installing it.

       The -T flag can be used to test the lease database file in a similar

       The -tf and -play options allow you to specify a file into which the
       entire startup state of the server and all the transactions it
       processes are either logged or played back from.  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

       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.

       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 of
       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 leaseā€”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 "vix.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 associted 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 facillitate
            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 pre-emptively.  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  - partner down
                 2  - normal
                 3  - communications interrupted
                 4  - resolution interrupted
                 5  - potential conflict
                 6  - recover
                 7  - recover done
                 8  - shutdown
                 9  - paused
                 10 - startup
                 11 - recover wait

            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.

       /etc/dhcpd.conf, /var/lib/dhcpd/dhcpd.leases, /var/run/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
       http://www.isc.org/.  Information about Nominum can be found at