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dhcpd(8)		    System Manager's Manual		      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 Dy-
       namic 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.

CONTRIBUTIONS
       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.

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.

       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 ad-
       dress using the DHCP protocol, dhcpd allocates an address for it.  Each
       client is assigned a lease, which expires after an amount of time  cho-
       sen  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 as-
       signed.

       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-as-
       signed addresses	once they are no longer	needed.	  It is	still possible
       to  dynamically assign addresses	to BOOTP clients, but some administra-
       tive process for	reclaiming addresses is	required.   By default,	leases
       are granted to BOOTP clients in perpetuity, although the	network	admin-
       istrator	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.

       The server either operates as a DHCPv6 server or	a DHCP server, but not
       both  at	 the same time.	To run as a DHCPv6 server, use the -6 flag. To
       run as a	DHCP server, use the -4	flag. If neither is used, the  default
       is to run as a DHCPv6 server.

       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 pur-
       poses.

       If dhcpd	should send replies to an address other	than the broadcast ad-
       dress (255.255.255.255),	the -s flag may	be used. It is followed	by ei-
       ther the	IP address or the host name to send replies to.	This option is
       only supported in IPv4.

       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 com-
       plete log of all	dhcp activity must be kept but syslogd is not reliable
       or  otherwise cannot be used.   Normally, dhcpd will log	all output us-
       ing 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 back-
       ground).

       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 op-
       tions 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	speci-
       fied.

       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
       way.

       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  pro-
       cesses  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
       -play.

       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.

       To find the version of dhcpd that will run, use the --version argument.
       Instead of running, the version will be printed.

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 ad-
       dresses 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 ad-
       dress  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  in-
       finity.	  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 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	 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 en-
       vironment 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 ac-
	    quired 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  as-
	    signed  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  at-
       tribute 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 re-
	    cently 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 re-
	    ceived 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,	   DB-
       DIR/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/.   Information  about  Nominum  can	 be  found  at
       http://www.nominum.com/.

								      dhcpd(8)

NAME | SYNOPSIS | DESCRIPTION | CONTRIBUTIONS | OPERATION | COMMAND LINE | 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

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