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dhcpd(8)							      dhcpd(8)

       dhcpd - Dynamic Host Configuration Protocol Server

       dhcpd  [	 -p  port  ] [ -f ] [ -d ] [ -q	] [ -t | -T ] [	-4 | -6	] [ -s
       server ]	[ -cf config-file ] [ -lf lease-file ] [ -pf pid-file ]	[  -tf
       trace-output-file ] [ -play trace-playback-file ] [ if0 [ ...ifN	] ]

       dhcpd --version

       The  Internet  Systems  Consortium  DHCP	 Server, dhcpd,	implements the
       Dynamic Host Configuration Protocol (DHCP) and the  Internet  Bootstrap
       Protocol	(BOOTP).  DHCP allows hosts on a TCP/IP	network	to request and
       be assigned IP addresses, and also to discover  information  about  the
       network to which	they are attached.  BOOTP provides similar functional-
       ity, with certain restrictions.

       The DHCP	protocol allows	a host which is	unknown	to the network	admin-
       istrator	to be automatically assigned a new IP address out of a pool of
       IP addresses for	its network.   In order	for this to work, the  network
       administrator  allocates	 address  pools	in each	subnet and enters them
       into the	dhcpd.conf(5) file.

       There are two versions of the DHCP  protocol  DHCPv4  and  DHCPv6.   At
       startup	the  server  may be started for	one or the other via the -4 or
       -6 arguments.

       On startup, dhcpd reads the dhcpd.conf file and stores a	list of	avail-
       able  addresses	on  each  subnet in memory.  When a client requests an
       address using the DHCP protocol,	dhcpd allocates	 an  address  for  it.
       Each  client is assigned	a lease, which expires after an	amount of time
       chosen by the administrator  (by	 default,  one	day).	Before	leases
       expire,	the clients to which leases are	assigned are expected to renew
       them in order to	continue to use	 the  addresses.   Once	 a  lease  has
       expired,	 the client to which that lease	was assigned is	no longer per-
       mitted to use the leased	IP address.

       In order	to keep	track of  leases  across  system  reboots  and	server
       restarts,  dhcpd	 keeps	a  list	 of  leases  it	 has  assigned	in the
       dhcpd.leases(5) file.   Before dhcpd grants  a  lease  to  a  host,  it
       records	the lease in this file and makes sure that the contents	of the
       file are	flushed	to disk.   This	ensures	that even in the  event	 of  a
       system crash, dhcpd will	not forget about a lease that it has assigned.
       On  startup,  after  reading  the  dhcpd.conf  file,  dhcpd  reads  the
       dhcpd.leases  file  to  refresh	its memory about what leases have been

       New leases are appended to the end of the dhcpd.leases file.   In order
       to  prevent the file from becoming arbitrarily large, from time to time
       dhcpd creates a new dhcpd.leases	file from its in-core lease  database.
       Once  this  file	 has  been  written  to	 disk, the old file is renamed
       dhcpd.leases~, and the new file is renamed dhcpd.leases.	  If the  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/,  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.

       The  names  of  the network interfaces on which dhcpd should listen for
       broadcasts may be specified on the command line.	 This should  be  done
       on  systems where dhcpd is unable to identify non-broadcast interfaces,
       but should not be required on other systems.  If	no interface names are
       specified  on  the  command line	dhcpd will identify all	network	inter-
       faces which are up, eliminating non-broadcast interfaces	 if  possible,
       and listen for DHCP broadcasts on each interface.

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

       -6     Run  as a	DHCPv6 server.	This is	the default and	cannot be com-
	      bined with -4.

       -p port
	      The udp port number on which dhcpd should	listen.	  If  unspeci-
	      fied  dhcpd  uses	the default port of 67.	 This is mostly	useful
	      for debugging purposes.

       -s address
	      Specify an address or host  name	to  which  dhcpd  should  send
	      replies  rather  than  the  broadcast address (
	      This option is only supported in IPv4.

       -f     Force dhcpd to run as a foreground process instead of as a  dae-
	      mon  in the background.  This is useful when running dhcpd under
	      a	debugger, or when running it out of inittab on System  V  sys-

       -d     Send log messages	to the standard	error descriptor.  This	can be
	      useful for debugging, and	also at	sites where a complete log  of
	      all  dhcp	 activity  must	be kept	but syslogd is not reliable or
	      otherwise	cannot be used.	  Normally, dhcpd will log all	output
	      using  the  syslog(3)  function  with  the  log  facility	set to
	      LOG_DAEMON.  Note	that -d	implies	-f (the	daemon will  not  fork
	      itself into the background).

       -q     Be quiet at startup.  This suppresses the	printing of the	entire
	      copyright	message	during startup.	 This might be desirable  when
	      starting dhcpd from a system startup script (e.g., /etc/rc).

       -t     Test the configuration file.  The	server tests the configuration
	      file for correct syntax, but will	not  attempt  to  perform  any
	      network  operations.   This can be used to test a	new configura-
	      tion file	automatically before installing	it.

       -T     Test the lease file.  The	server tests the lease file  for  cor-
	      rect  syntax, but	will not attempt to perform any	network	opera-
	      tions.   This can	be used	to test	a new 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.

	      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.

       The  syntax  of	the dhcpd.conf(5) file is discussed separately.	  This
       section should be used as an overview of	the configuration process, and
       the dhcpd.conf(5) documentation should be consulted for detailed	refer-
       ence information.

       dhcpd needs to know the subnet numbers and netmasks of all subnets  for
       which  it will be providing service.   In addition, in order to dynami-
       cally allocate addresses, it must be assigned one  or  more  ranges  of
       addresses on each subnet	which it can in	turn assign to client hosts as
       they boot.   Thus, a very simple	configuration providing	 DHCP  support
       might look like this:

	    subnet netmask {

       Multiple	address	ranges may be specified	like this:

	    subnet netmask {

       If  a  subnet  will  only be provided with BOOTP	service	and no dynamic
       address assignment, the range clause can	be left	out entirely, but  the
       subnet statement	must appear.

Lease Lengths
       DHCP  leases  can  be  assigned	almost any length from zero seconds to
       infinity.   What	lease length makes sense for any given subnet, or  for
       any given installation, will vary depending on the kinds	of hosts being

       For example, in an office environment where systems are added from time
       to  time	 and  removed  from  time  to time, but	move relatively	infre-
       quently,	it might make sense to allow lease times of a month  or	 more.
       In  a final test	environment on a manufacturing floor, it may make more
       sense to	assign a maximum lease length of 30 minutes - enough  time  to
       go  through a simple test procedure on a	network	appliance before pack-
       aging it	up for delivery.

       It is possible to specify two lease lengths: the	 default  length  that
       will  be	 assigned  if  a  client  doesn't ask for any particular lease
       length, and a maximum lease length.   These are specified as clauses to
       the subnet command:

	    subnet netmask {
	      default-lease-time 600;
	      max-lease-time 7200;

       This  particular	 subnet	 declaration specifies a default lease time of
       600 seconds (ten	minutes), and a	maximum	lease  time  of	 7200  seconds
       (two  hours).	Other  common  values would be 86400 (one day),	604800
       (one week) and 2592000 (30 days).

       Each subnet need	not have the same lease--in  the  case	of  an	office
       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;
	      filename "/tftpboot/haagen.boot";

       DHCP (and also  BOOTP  with  Vendor  Extensions)	 provide  a  mechanism
       whereby the server can provide the client with information about	how to
       configure its network interface (e.g., subnet mask), and	also  how  the
       client  can access various network services (e.g., DNS, IP routers, and
       so on).

       These options can be specified on a per-subnet basis,  and,  for	 BOOTP
       clients,	also on	a per-client basis.   In the event that	a BOOTP	client
       declaration specifies options that are also  specified  in  its	subnet
       declaration,  the  options  specified  in  the  client declaration take
       precedence.   A reasonably complete DHCP	configuration might look some-
       thing like this:

	    subnet netmask {
	      default-lease-time 600 max-lease-time 7200;
	      option subnet-mask;
	      option broadcast-address;
	      option routers;
	      option domain-name-servers,;
	      option domain-name "";

       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 configu-
       ration while it is running, without stopping it,	modifying its database
       files,  and restarting it.  This	capability is currently	provided using
       OMAPI - an API for manipulating remote objects.	OMAPI clients  connect
       to  the	server	using  TCP/IP,	authenticate, and can then examine the
       server's	current	status and make	changes	to it.

       Rather than implementing	the underlying OMAPI protocol  directly,  user
       programs	 should	 use  the  dhcpctl API or OMAPI	itself.	  Dhcpctl is a
       wrapper that handles some of the	housekeeping chores  that  OMAPI  does
       not  do automatically.	Dhcpctl	and OMAPI are documented in dhcpctl(3)
       and omapi(3).

       OMAPI exports objects, which can	then be	examined and  modified.	   The
       DHCP  server exports the	following objects: lease, host,	failover-state
       and group.   Each object	has a number of	 methods  that	are  provided:
       lookup,	create,	 and destroy.	In addition, it	is possible to look at
       attributes that are stored on objects, and  in  some  cases  to	modify
       those attributes.

       Leases  can't currently be created or destroyed,	but they can be	looked
       up to examine and modify	their state.

       Leases have the following attributes:

       state integer lookup, examine
	    1 =	free
	    2 =	active
	    3 =	expired
	    4 =	released
	    5 =	abandoned
	    6 =	reset
	    7 =	backup
	    8 =	reserved
	    9 =	bootp

       ip-address data lookup, examine
	    The	IP address of the lease.

       dhcp-client-identifier data lookup, examine, update
	    The	client identifier that the client used when  it	 acquired  the
	    lease.   Not  all  clients send client identifiers,	so this	may be

       client-hostname data examine, update
	    The	value the client sent in the host-name option.

       host handle examine
	    the	host declaration associated with this lease, if	any.

       subnet handle examine
	    the	subnet object associated with this lease (the subnet object is
	    not	currently supported).

       pool handle examine
	    the	pool object associated with this lease (the pool object	is not
	    currently supported).

       billing-class handle examine
	    the	handle to the class to which this lease	is  currently  billed,
	    if any (the	class object is	not currently supported).

       hardware-address	data examine, update
	    the	 hardware  address  (chaddr)  field sent by the	client when it
	    acquired its lease.

       hardware-type integer examine, update
	    the	type of	the network interface that the client reported when it
	    acquired its lease.

       ends time examine
	    the	time when the lease's current state ends, as understood	by the

       tstp time examine
	    the	time when the lease's current state ends, as understood	by the
       tsfp time examine
	    the	 adjusted  time	when the lease's current state ends, as	under-
	    stood by the failover peer (if there is  no	 failover  peer,  this
	    value  is  undefined).   Generally this value is only adjusted for
	    expired, released, or reset	leases while the server	 is  operating
	    in	partner-down state, and	otherwise is simply the	value supplied
	    by the peer.
       atsfp time examine
	    the	actual tsfp value sent from the	peer.  This value is forgotten
	    when  a lease binding state	change is made,	to facilitate retrans-
	    mission logic.

       cltt time examine
	    The	time of	the last transaction with the client on	this lease.

       Hosts can be created, destroyed,	looked up, examined and	modified.   If
       a  host declaration is created or deleted using OMAPI, that information
       will be recorded	in the	dhcpd.leases  file.    It  is  permissible  to
       delete host declarations	that are declared in the dhcpd.conf file.

       Hosts have the following	attributes:

       name data lookup, examine, modify
	    the	name of	the host declaration.	This name must be unique among
	    all	host declarations.

       group handle examine, modify
	    the	named group associated with the	host declaration, if there  is

       hardware-address	data lookup, examine, modify
	    the	 link-layer  address that will be used to match	the client, if
	    any.  Only valid if	hardware-type is also present.

       hardware-type integer lookup, examine, modify
	    the	type of	the network interface that will	be used	to  match  the
	    client,  if	any.   Only valid if hardware-address is also present.

       dhcp-client-identifier data lookup, examine, modify
	    the	dhcp-client-identifier option that will	be used	to  match  the
	    client, if any.

       ip-address data examine,	modify
	    a  fixed  IP  address  which  is  reserved	for a DHCP client that
	    matches this host declaration.    The  IP  address	will  only  be
	    assigned  to  the client if	it is valid for	the network segment to
	    which the client is	connected.

       statements data modify
	    a list of statements in the	format of  the	dhcpd.conf  file  that
	    will  be executed whenever a message from the client is being pro-

       known integer examine, modify
	    if nonzero,	indicates that a client	matching this host declaration
	    will  be  treated  as  known  in pool permit lists.	  If zero, the
	    client will	not be treated as known.

       Named groups can	be created, destroyed, looked up, examined  and	 modi-
       fied.   If  a group declaration is created or deleted using OMAPI, that
       information will	be recorded in the dhcpd.leases	file.  It is permissi-
       ble  to	delete	group declarations that	are declared in	the dhcpd.conf

       Named groups currently can only be associated with hosts	- this	allows
       one  set	of statements to be efficiently	attached to more than one host

       Groups have the following attributes:

       name data
	    the	name of	the group.  All	groups that are	 created  using	 OMAPI
	    must have names, and the names must	be unique among	all groups.

       statements data
	    a  list  of	 statements  in	the format of the dhcpd.conf file that
	    will be executed whenever a	message	from a client whose host  dec-
	    laration references	this group is processed.

       The  control object allows you to shut the server down.	 If the	server
       is doing	failover with another peer, it will make  a  clean  transition
       into  the  shutdown  state and notify its peer, so that the peer	can go
       into partner down, and then record the "recover"	 state	in  the	 lease
       file so that when the server is restarted, it will automatically	resyn-
       chronize	with its peer.

       On shutdown the server will also	attempt	to cleanly shut	down all OMAPI
       connections.   If  these	 connections do	not go down cleanly after five
       seconds,	they are shut down preemptively.  It can take as  much	as  25
       seconds from the	beginning of the shutdown process to the time that the
       server actually exits.

       To shut the server down,	open its control  object  and  set  the	 state
       attribute to 2.

       The  failover-state  object  is the object that tracks the state	of the
       failover	protocol as it is being	managed	for  a	given  failover	 peer.
       The failover object has the following attributes	(please	see dhcpd.conf
       (5) for explanations about what these attributes	mean):

       name data examine
	    Indicates the name of the failover peer relationship, as described
	    in the server's dhcpd.conf file.

       partner-address data examine
	    Indicates the failover partner's IP	address.

       local-address data examine
	    Indicates the IP address that is being used	by the DHCP server for
	    this failover pair.

       partner-port data examine
	    Indicates the TCP port on which the	failover partner is  listening
	    for	failover protocol connections.

       local-port data examine
	    Indicates  the  TCP	port on	which the DHCP server is listening for
	    failover protocol connections for this failover pair.

       max-outstanding-updates integer examine
	    Indicates the number of updates that can be	outstanding and	 unac-
	    knowledged at any given time, in this failover relationship.

       mclt integer examine
	    Indicates  the maximum client lead time in this failover relation-

       load-balance-max-secs integer examine
	    Indicates the maximum value	for the	secs field in a	client request
	    before load	balancing is bypassed.

       load-balance-hba	data examine
	    Indicates  the  load balancing hash	bucket array for this failover

       local-state integer examine, modify
	    Indicates the present state	of the DHCP server  in	this  failover
	    relationship.   Possible values for	state are:

		 1   - startup
		 2   - normal
		 3   - communications interrupted
		 4   - partner down
		 5   - potential conflict
		 6   - recover
		 7   - paused
		 8   - shutdown
		 9   - recover done
		 10  - resolution interrupted
		 11  - conflict	done
		 254 - recover wait

	    (Note  that	 some  of  the	above  values  have changed since DHCP

	    In general it is not a good	idea to	make changes  to  this	state.
	    However,  in  the  case  that  the failover	partner	is known to be
	    down, it can be useful to set the DHCP server's failover state  to
	    partner  down.   At	this point the DHCP server will	take over ser-
	    vice of the	failover partner's leases as  soon  as	possible,  and
	    will  give	out  normal  leases, not leases	that are restricted by
	    MCLT.   If you do put the DHCP server into the  partner-down  when
	    the	other DHCP server is not in the	partner-down state, but	is not
	    reachable, IP address  assignment  conflicts  are  possible,  even
	    likely.    Once  a server has been put into	partner-down mode, its
	    failover partner must not be brought back online until  communica-
	    tion is possible between the two servers.

       partner-state integer examine
	    Indicates the present state	of the failover	partner.

       local-stos integer examine
	    Indicates  the  time  at which the DHCP server entered its present
	    state in this failover relationship.

       partner-stos integer examine
	    Indicates the time at  which  the  failover	 partner  entered  its
	    present state.

       hierarchy integer examine
	    Indicates  whether the DHCP	server is primary (0) or secondary (1)
	    in this failover relationship.

       last-packet-sent	integer	examine
	    Indicates the time at which	the most recent	 failover  packet  was
	    sent by this DHCP server to	its failover partner.

       last-timestamp-received integer examine
	    Indicates  the  timestamp  that  was  on the failover message most
	    recently received from the failover	partner.

       skew integer examine
	    Indicates the skew between the failover partner's clock  and  this
	    DHCP server's clock

       max-response-delay integer examine
	    Indicates  the  time  in  seconds  after  which,  if no message is
	    received from the failover partner,	the partner is assumed	to  be
	    out	of communication.

       cur-unacked-updates integer examine
	    Indicates  the  number  of update messages that have been received
	    from the failover partner but not yet processed.

       ETCDIR/dhcpd.conf,	 DBDIR/dhcpd.leases,	     RUNDIR/,

       dhclient(8), dhcrelay(8), dhcpd.conf(5),	dhcpd.leases(5)

       dhcpd(8)	 was  originally  written  by  Ted Lemon under a contract with
       Vixie Labs.  Funding for	this project was provided by Internet  Systems
       Consortium.    Version 3	of the DHCP server was funded by Nominum, Inc.
       Information  about  Internet  Systems  Consortium   is	available   at



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