dhcpd(8)                                                              dhcpd(8)



NAME
       dhcpd - Dynamic Host Configuration Protocol Server

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

       dhcpd --version

DESCRIPTION
       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 functional-
       ity, with certain restrictions.

OPERATION
       The  DHCP protocol allows a host which is unknown to the network admin-
       istrator 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 avail-
       able 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  per-
       mitted 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
       assigned.

       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  possi-
       ble to dynamically assign addresses to BOOTP clients, but some adminis-
       trative 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.

COMMAND LINE
       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  inter-
       faces  which  are up, eliminating non-broadcast interfaces if possible,
       and listen for DHCP broadcasts on each interface.


COMMAND LINE OPTIONS
       -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.

       -p port
              The  udp  port number on which dhcpd should listen.  If unspeci-
              fied 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  (255.255.255.255).
              This option is only supported in IPv4.

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

       -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  configura-
              tion file automatically before installing it.

       -T     Test  the  lease file.  The server tests the lease file for cor-
              rect syntax, but will not attempt to perform any network  opera-
              tions.   This can be used to test a new lease file automatically
              before installing it.

       -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 exist-
              ing lease file with its test data.  The DHCP server will  refuse
              to  operate  in  playback  mode  unless you specify an alternate
              lease file.

       --version
              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 impor-
       tance 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.

       --no-pid
              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.


CONFIGURATION
       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 refer-
       ence information.


Subnets
       dhcpd  needs to know the subnet numbers and netmasks of all subnets for
       which it will be providing service.  In addition, in order  to  dynami-
       cally  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 239.252.197.0 netmask 255.255.255.0 {
              range 239.252.197.10 239.252.197.250;
            }

       Multiple address ranges may be specified like this:

            subnet 239.252.197.0 netmask 255.255.255.0 {
              range 239.252.197.10 239.252.197.107;
              range 239.252.197.113 239.252.197.250;
            }

       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
       served.

       For example, in an office environment where systems are added from time
       to time and removed from time  to  time,  but  move  relatively  infre-
       quently,  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  pack-
       aging 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 239.252.197.0 netmask 255.255.255.0 {
              range 239.252.197.10 239.252.197.107;
              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 inter-
       face'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;
              fixed-address 239.252.197.9;
              filename "/tftpboot/haagen.boot";
            }

Options
       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 some-
       thing like this:

            subnet 239.252.197.0 netmask 255.255.255.0 {
              range 239.252.197.10 239.252.197.250;
              default-lease-time 600 max-lease-time 7200;
              option subnet-mask 255.255.255.0;
              option broadcast-address 239.252.197.255;
              option routers 239.252.197.1;
              option domain-name-servers 239.252.197.2, 239.252.197.3;
              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;
              fixed-address 239.252.197.9;
              filename "/tftpboot/haagen.boot";
              option domain-name-servers 192.5.5.1;
              option domain-name "vix.com";
            }

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

OMAPI
       The DHCP server provides the capability to modify some of its  configu-
       ration 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.

THE LEASE OBJECT
       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
            empty.

       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
            client.

       tstp time examine
            the time when the lease's current state ends, as understood by the
            server.
       tsfp time examine
            the adjusted time when the lease's current state ends,  as  under-
            stood  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  retrans-
            mission logic.

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

THE HOST OBJECT
       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
            one.

       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 pro-
            cessed.

       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.

THE GROUP OBJECT
       Named groups can be created, destroyed, looked up, examined  and  modi-
       fied.   If  a group declaration is created or deleted using OMAPI, that
       information will be recorded in the dhcpd.leases file.  It is permissi-
       ble  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
       declaration.

       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  dec-
            laration references this group is processed.

THE CONTROL OBJECT
       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 resyn-
       chronize 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
       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  unac-
            knowledged at any given time, in this failover relationship.

       mclt integer examine
            Indicates  the maximum client lead time in this failover relation-
            ship.

       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
            relationship.

       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
            3.0.x.)

            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 ser-
            vice 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  communica-
            tion 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.

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

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

AUTHOR
       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
       https://www.isc.org/.



                                                                      dhcpd(8)

You can also request any man page by name and (optionally) by section:

Command: 
Section: 
Architecture: 
Collection: 
 

Use the DEFAULT collection to view manual pages for third-party software.


©1994 Man-cgi 1.15, Panagiotis Christias <christia@softlab.ntua.gr>
©1996-2014 Modified for NetBSD by Kimmo Suominen