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NetBSD 6.1.5 - man page for dhcpd (netbsd section 8)

dhcpd(8)										 dhcpd(8)

       dhcpd - Dynamic Host Configuration Protocol Server

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

       The Internet Systems Consortium DHCP Server, dhcpd, implements the Dynamic Host Configura-
       tion  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 functionality, 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 administrator to be  auto-
       matically  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 available 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 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

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

       BOOTP support is also provided by this server.  Unlike DHCP, the BOOTP protocol	does  not
       provide	a  protocol for recovering dynamically-assigned addresses once they are no longer
       needed.	 It is still possible to dynamically assign addresses to BOOTP clients, but  some
       administrative  process	for  reclaiming  addresses  is required.   By default, leases are
       granted to BOOTP clients in perpetuity, although the network administrator may set an ear-
       lier 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
       database, dhcpd does not automatically restart  itself  when  it  sees  a  change  to  the
       dhcpd.conf file.

       Note:  We  get  a  lot of complaints about this.   We realize that it would be nice if one
       could send a SIGHUP to the server and have it reload the database.   This is  not  techni-
       cally  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.

       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 purposes.

       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 use-
       ful 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.

       Dhcpd can be made to use an alternate configuration file with the -cf flag, or  an  alter-
       nate  lease  file  with	the -lf 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 desir-
       able to print out the entire copyright message on startup.   To avoid printing  this  mes-
       sage, the -q flag may be specified.

       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  cor-
       rect 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 processes 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

       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 reference 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 dynamically 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  depend-
       ing 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 infrequently, 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 packaging it up for deliv-

       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 min-
       utes),  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 manu-
       facturing  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 interface'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 declara-
       tion take precedence.   A reasonably complete DHCP configuration might look something like

	    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 configuration  while  it  is
       running, without stopping it, modifying its database files, and restarting it.  This capa-
       bility 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 house-
       keeping 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

       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 sup-

       pool handle examine
	    the pool object associated with this lease (the pool object  is  not  currently  sup-

       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

       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  time when the lease's current state ends, as understood by the failover peer (if
	    there is no failover peer, this value is undefined).

       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

       Hosts have the following attributes:

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

       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  decla-
	    ration.    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 when-
	    ever a message from the client is being processed.

       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 modified.  If a group dec-
       laration  is  created  or  deleted  using  OMAPI, that information will be recorded in the
       dhcpd.leases file.  It is permissible 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 state-
       ments 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 when-
	    ever a message from a client whose host declaration references  this  group  is  pro-

       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  resynchronize
       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  pre-emp-
       tively.	 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

       partner-port data examine
	    Indicates the TCP port on which the failover partner is listening for failover proto-
	    col 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  unacknowledged  at  any
	    given time, in this failover relationship.

       mclt integer examine
	    Indicates the maximum client lead time in this failover relationship.

       load-balance-max-secs integer examine
	    Indicates  the  maximum value for the secs field in a client request before load bal-
	    ancing 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.    Pos-
	    sible values for state are:

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

	    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 service 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 communication is possible between the two

       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

       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/dhcpd.conf, /var/db/dhcpd.leases, /var/run/dhcpd.pid, /var/db/dhcpd.leases~.

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


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