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  ]  [ -user user ] [ -group group ] [ -chroot dir ] [
       -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.

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
       address using the DHCP protocol, dhcpd allocates	 an  address  for  it.
       Each  client is assigned a lease, which expires after an amount of time
       chosen by the administrator  (by	 default,  one	day).	Before	leases
       expire,	the clients to which leases are assigned are expected to renew
       them in order to continue to use	 the  addresses.   Once	 a  lease  has
       expired,	 the client to which that lease was assigned is no longer per-
       mitted to use the leased IP address.

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

       New leases are appended to the end of the dhcpd.leases file.   In order
       to  prevent the file from becoming arbitrarily large, from time to time
       dhcpd creates a new dhcpd.leases file from its in-core lease  database.
       Once  this  file	 has  been  written  to	 disk, the old file is renamed
       dhcpd.leases~, and the new file is renamed dhcpd.leases.	  If the  sys-
       tem  crashes in the middle of this process, whichever dhcpd.leases file
       remains will contain all the lease information, so there is no need for
       a special crash recovery process.

       BOOTP  support is also provided by this server.	Unlike DHCP, the BOOTP
       protocol does  not  provide  a  protocol	 for  recovering  dynamically-
       assigned addresses once they are no longer needed.   It is still possi-
       ble to dynamically assign addresses to BOOTP clients, but some adminis-
       trative	process	 for  reclaiming  addresses is required.   By default,
       leases are granted to BOOTP clients in perpetuity, although the network
       administrator  may set an earlier cutoff date or a shorter lease length
       for BOOTP leases if that makes sense.

       BOOTP clients may also be served in the old standard way, which	is  to
       simply  provide	a  declaration	in  the dhcpd.conf file for each BOOTP
       client, permanently assigning an address to each client.

       Whenever changes are  made  to  the  dhcpd.conf	file,  dhcpd  must  be
       restarted.    To	 restart  dhcpd,  send	a  SIGTERM  (signal 15) to the
       process ID contained in /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.

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
       address (255.255.255.255), 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-
       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
       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-
       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.

       -user user
	      Setuid  to  user after completing privileged operations, such as
	      creating sockets that listen on privileged ports.

       -group group
	      Setgid to group after completing privileged operations, such  as
	      creating sockets that listen on privileged ports.

       -chroot dir
	      Chroot to directory after processing the command line arguments,
	      but before reading the configuration file.

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

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

	    subnet 239.252.197.0 netmask 255.255.255.0 {
	      range 239.252.197.10 239.252.197.250;
	    }

       Multiple address ranges may be specified like this:

	    subnet 239.252.197.0 netmask 255.255.255.0 {
	      range 239.252.197.10 239.252.197.107;
	      range 239.252.197.113 239.252.197.250;
	    }

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

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

       For example, in an office environment where systems are added from time
       to time and removed from time  to  time,	 but  move  relatively	infre-
       quently,	 it  might make sense to allow lease times of a month 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
       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
       /etc/dhcp/dhcpd.conf, /var/lib/dhcpd/dhcpd.leases,  /var/run/dhcpd.pid,
       /var/lib/dhcpd/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)