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       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/, 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 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 "";

       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 "";

       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.


       /etc/dhcp3/dhcpd.conf, /var/lib/dhcp3/dhcpd.leases, /var/run/,


       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   Information  about  Nominum  can  be  found  at