Provided by: isc-dhcp-server_4.3.3-5ubuntu11_i386 bug


       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  ]  [
       --no-pid ] [ -user user ] [ -group group ] [ -chroot dir ] [ -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
       functionality, with certain restrictions.


       The  DHCP  protocol  allows  a  host  which  is  unknown to the network
       administrator 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
       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 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/, 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 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
       interfaces  which  are  up,  eliminating  non-broadcast  interfaces  if
       possible, and listen for DHCP broadcasts on each interface.


       -4     Run as a DHCP server. This is the default and cannot be combined
              with -6.

       -6     Run as a DHCPv6 server. This cannot be combined with -4.

       -p port
              The   udp   port  number  on  which  dhcpd  should  listen.   If
              unspecified 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
              daemon in the background.  This is  useful  when  running  dhcpd
              under  a debugger, or when running it out of inittab on System V

       -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
              configuration file automatically before installing it.

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

       -user user
              Setuid to user after completing privileged operations,  such  as
              creating  sockets  that  listen  on privileged ports.  This also
              causes the lease file to be owned by user.  This option is  only
              available  if  the  code  was  compiled  with the PARANOIA patch
              (./configure --enable-paranoia).

       -group group
              Setgid to group after completing privileged operations, such  as
              creating  sockets  that  listen  on privileged ports.  This also
              causes the lease  file  to  use  group.   This  option  is  only
              available  if  the  code  was  compiled  with the PARANOIA patch
              (./configure --enable-paranoia).

       -chroot dir
              Chroot to directory.  This may occur before or after reading the
              configuration  files  depending on whether the code was compiled
              with the  EARLY_CHROOT  option  enabled  (./configure  --enable-
              early-chroot).   This  option  is only available if the code was
              compiled  with  the  PARANOIA   patch   (./configure   --enable-

       -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
              existing  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  its  files.   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.

       -cf config-file
              Path to alternate configuration file.

       -lf lease-file
              Path to alternate lease file.

       -pf pid-file
              Path to alternate pid file.

              Option  to  disable  writing  pid files.  By default the program
              will write a pid file.  If the  program  is  invoked  with  this
              option it will not check for an existing server process.


       During  operations  the  server  may  use multiple UDP and TCP ports to
       provide different functions.  Which ports are opened  depends  on  both
       the  way  you compiled your code and the configuration you supply.  The
       following should provide you an idea of what ports may be in use.

       Normally a DHCPv4 server will open a raw UDP socket to receive and send
       most  DHCPv4  packets.   It also opens a fallback UDP socket for use in
       sending unicast packets.  Normally these will both use the  well  known
       port number for BOOTPS.

       For  each DHCPv4 failover peer you list in the configuartion file there
       will be a TCP socket listening for connections on the ports  specififed
       in  the  configuration  file.   When  the  peer  connects there will be
       another socket for the established  connection.   For  the  established
       connection  the side (primary or secondary) opening the connection will
       use a random port.

       For  DHCPv6  the  server  opens  a  UDP  socket  on  the   well   known
       dhcpv6-server port.

       The  server  opens  an  icmp socket for doing ping requests to check if
       addresses are in use.

       If you have included an omapi-port statement in your configuration file
       then the server will open a TCP socket on that port to listen for OMPAI
       connections.  When something connects another port will be used for the
       established connection.

       When  DDNS  is enabled at compile time (see includes/site.h) the server
       will open both a v4 and a v6 UDP socket on random ports.   These  ports
       are opened even if DDNS is disabled in the configuration 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
       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 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
       infrequently, 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 packaging 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  leaseā€”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
       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 declaration take
       precedence.   A  reasonably  complete  DHCP  configuration  might  look
       something 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
       configuration 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
            understood 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
            retransmission 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

       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 declaration 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 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
            declaration 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
       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 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
            unacknowledged at any given time, in this failover relationship.

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

       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
            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 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/dhcp/dhcpd.leases,  /var/run/,


       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