Provided by: dhcp_2.0pl5-19.4_i386 bug

NAME

       dhcpd - Dynamic Host Configuration Protocol Server

SYNOPSIS

       dhcpd [ -p port ] [ -f ] [ -d ] [ -q ] [ -cf config-file ] [ -lf lease-
       file ] [ if0 [ ...ifN ] ]

DESCRIPTION

       The Internet Software 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.

OPERATION

       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.

       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
       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
       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/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 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
       interfaces  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.   If  the  -p  flag  is  specified,  the server will transmit
       responses to clients at a port number that is one greater than the  one
       specified  - i.e., if you specify -p 67, then the server will listen on
       port 67 and transmit to port 68.  Datagrams that must go through  relay
       agents  are sent to the port number specified with the -p flag - if you
       wish to use alternate port numbers, you must configure any relay agents
       you are using to use the same alternate port numbers.

       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
       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 alternate 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 desirable to print  out  the  entire  copyright  message  on
       startup.    To  avoid  printing  this  message,  the  -q  flag  may  be
       specified.

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
       reference 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
       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 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
       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 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
       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;
              fixed-address 239.252.197.9;
              filename "/tftpboot/haagen.boot";
            }

Options

       DHCP  (and  also  BOOTP  with  Vendor  Extensions) provides 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.    An  reasonably  complete  DHCP  configuration might look
       something 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).

FILES

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

SEE ALSO

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

AUTHOR

       dhcpd(8)  was  written  by  Ted Lemon <mellon@vix.com> under a contract
       with Vixie Labs.    Funding  for  this  project  was  provided  by  the
       Internet Software Corporation.  Information about the Internet Software
       Consortium can be found at http://www.isc.org/isc.

                                                                      dhcpd(8)