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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 ] [ -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 functional‐
       ity, with certain restrictions.

       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

       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.

       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.

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

       -6     Run as a DHCPv6 server.  This is the default and cannot be  com‐
              bined 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  (
              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‐

       -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.

       -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  avail‐
              able if the code was compiled with the PARANOIA patch (./config‐
              ure --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-para‐

       -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.

              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.

              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 pro‐
       vide different functions.  Which ports are opened depends on  both  the
       way  you compiled your code and the configuration you supply.  The fol‐
       lowing 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 configuartion file there
       will be a TCP socket listening for connections on the ports  specififed
       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.

       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.

       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 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 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 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 envi‐
       ronment 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;
              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  some‐
       thing 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 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.

       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 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.

       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  pro‐

       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 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

       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 dec‐
            laration 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 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 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‐

       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  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.

       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

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