Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
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)

NAME | SYNOPSIS | DESCRIPTION | OPERATION | COMMAND LINE | COMMAND LINE OPTIONS | CONFIGURATION | Subnets | Lease Lengths | BOOTP Support | Options | OMAPI | THE LEASE OBJECT | THE HOST OBJECT | THE GROUP OBJECT | THE CONTROL OBJECT | THE FAILOVER-STATE OBJECT | FILES | SEE ALSO | AUTHOR

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=dhcpd&manpath=FreeBSD+10.1-RELEASE+and+Ports>

home | help