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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 ] [  -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  sys‐
       tem  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 data‐
       base, 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 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 (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 leaes 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 it's 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.

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 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;
	      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)
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