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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.

       This software is free software.	At various times its  development  has
       been underwritten by various organizations, including the ISC and Vixie
       Enterprises.  The development of 3.0 has been funded almost entirely by
       Nominum, Inc.

       At  this point development is being shepherded by Ted Lemon, and hosted
       by the ISC, but the future of this project depends on you.  If you have
       features you want, please consider implementing them.

       The  DHCP protocol allows a host which is unknown to the network 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
       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 /var/run/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.

       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‐

       If dhcpd should send replies to an address  other  than	the  broadcast
       address	(,  the -s flag may be used. It is followed by
       either 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
       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 back‐

       Dhcpd can be made to use an alternate configuration file with  the  -cf
       flag,  an  alternate  lease file with the -lf flag, or an alternate pid
       file with the -pf flag.	 Because of the importance of using  the  same
       lease  database	at  all	 times when running dhcpd in production, these
       options should be used only for testing lease files or  database	 files
       in a non-production environment.

       When starting dhcpd up from a system startup script (e.g., /etc/rc), it
       may not be desirable to print  out  the	entire	copyright  message  on
       startup.	   To  avoid  printing this message, the -q flag may be speci‐

       The DHCP server reads two files on startup: a configuration file, and a
       lease  database.	   If the -t flag is specified, the server will simply
       test the configuration file for correct syntax, but will not attempt to
       perform	any  network  operations.   This can be used to test the a new
       configuration file automatically before installing it.

       The -T flag can be used to test the lease database file	in  a  similar

       The  -tf	 and  -play options allow you to specify a file into which the
       entire startup state of the server and all  the	transactions  it  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

       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.

       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 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 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 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;
	      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 "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;
	      filename "/tftpboot/haagen.boot";
	      option domain-name-servers;
	      option domain-name "vix.com";

       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.

       /etc/dhcp/dhcpd.conf, /var/lib/dhcpd/dhcpd.leases,  /var/run/dhcpd.pid,

       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
       https://www.isc.org/.   Information  about  Nominum  can	 be  found  at


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