dhcpd.leases(5)                                                dhcpd.leases(5)



NAME
       dhcpd.leases - DHCP client lease database

DESCRIPTION
       The Internet Systems Consortium DHCP Server keeps a persistent database
       of leases that it has assigned.  This database  is  a  free-form  ASCII
       file  containing a series of lease declarations.  Every time a lease is
       acquired, renewed or released, its new value is recorded at the end  of
       the  lease  file.   So if more than one declaration appears for a given
       lease, the last one in the file is the current one.

       When dhcpd is first installed, there is no lease  database.    However,
       dhcpd  requires  that a lease database be present before it will start.
       To make the initial lease database, just create an  empty  file  called
       DBDIR/dhcpd.leases.   You can do this with:

            touch DBDIR/dhcpd.leases

       In  order to prevent the lease database from growing without bound, the
       file is rewritten from time to time.   First, a temporary  lease  data-
       base  is created and all known leases are dumped to it.   Then, the old
       lease database is renamed  DBDIR/dhcpd.leases~.    Finally,  the  newly
       written lease database is moved into place.

       In  order  to  process both DHCPv4 and DHCPv6 messages you will need to
       run two separate  instances  of  the  dhcpd  process.   Each  of  these
       instances will need it's own lease file.  You can use the -lf option on
       the server's command line to specify a different lease  file  name  for
       one or both servers.

FORMAT
       Lease  descriptions  are  stored in a format that is parsed by the same
       recursive  descent  parser  used  to   read   the   dhcpd.conf(5)   and
       dhclient.conf(5)  files.   Lease  files can contain lease declarations,
       and  also  group  and  subgroup  declarations,  host  declarations  and
       failover state declarations.  Group, subgroup and host declarations are
       used to record objects created using the OMAPI protocol.

       The lease file is a log-structured file - whenever a lease changes, the
       contents of that lease are written to the end of the file.   This means
       that it is entirely possible and quite reasonable for there to  be  two
       or  more  declarations  of the same lease in the lease file at the same
       time.   In that case,  the  instance  of  that  particular  lease  that
       appears last in the file is the one that is in effect.

       Group,  subgroup and host declarations in the lease file are handled in
       the same manner, except that if any of these  objects  are  deleted,  a
       rubout  is  written to the lease file.   This is just the same declara-
       tion, with { deleted; } in the scope of  the  declaration.    When  the
       lease  file  is  rewritten, any such rubouts that can be eliminated are
       eliminated.   It is possible to delete a declaration in the  dhcpd.conf
       file;  in  this  case,  the  rubout  can  never  be eliminated from the
       dhcpd.leases file.

COMMON STATEMENTS FOR LEASE DECLARATIONS
       While the lease file formats for DHCPv4 and DHCPv6 are  different  they
       share  many  common  statements and structures.  This section describes
       the common statements while the succeeding sections describe the proto-
       col specific statements.

       Dates

       A  date  is specified in two ways, depending on the configuration value
       for the db-time-format parameter.  If it was set to default,  then  the
       date fields appear as follows:

       weekday year/month/day hour:minute:second

       The weekday is present to make it easy for a human to tell when a lease
       expires - it's specified as a number from zero to six, with zero  being
       Sunday.   The  day  of week is ignored on input.  The year is specified
       with the century, so it should generally  be  four  digits  except  for
       really long leases.  The month is specified as a number starting with 1
       for January.  The day of the month is likewise specified starting  with
       1.   The hour is a number between 0 and 23, the minute a number between
       0 and 59, and the second also a number between 0 and 59.

       Lease times are specified in Universal Coordinated Time (UTC),  not  in
       the  local time zone.  There is probably nowhere in the world where the
       times recorded on a lease are always the same as wall clock times.   On
       most  unix  machines, you can display the current time in UTC by typing
       date -u.

       If the db-time-format was configured to local,  then  the  date  fields
       appear as follows:

        epoch  <seconds-since-epoch>;  #  <day-name> <month-name> <day-number>
       <hours>:<minutes>:<seconds> <year>

       The seconds-since-epoch is as according to  the  system's  local  clock
       (often  referred  to  as "unix time").  The # symbol supplies a comment
       that describes what actual time this is as according  to  the  system's
       configured timezone, at the time the value was written.  It is provided
       only for human inspection.

       If a lease will never expire, date is never instead of an actual  date.

       General Variables

       As part of the processing of a lease information may be attached to the
       lease structure, for example the DDNS information or if you  specify  a
       variable  in  your  configuration  file.   Some of these, like the DDNS
       information, have specific descriptions below.  For others, such as any
       you might define, a generic line of the following will be included.

       set variable = value;

       The  set statement sets the value of a variable on the lease.  For gen-
       eral information on variables, see the dhcp-eval(5) manual page.

       DDNS Variables

       The ddns-text and ddns-dhcid variables

       These variables are used to record the value of the client's identification
       record when the server has updated DNS for a particular lease.  The text
       record is used with the interim DDNS update style while the dhcid record
       is used for the standard DDNS update style.

       The ddns-fwd-name variable

       This variable records the value of the name used in
       updating the client's A record if a DDNS update has been successfully
       done by the server.   The server may also have used this name to
       update the client's PTR record.

       The ddns-client-fqdn variable

       If the server is configured both to use the interim or standard DDNS update
       style, and to allow clients to update their own FQDNs, then if the
       client did in fact update its own FQDN, the
       ddns-client-fqdn variable records the name that the client has
       indicated it is using.   This is the name that the server will have
       used to update the client's PTR record in this case.

       The ddns-rev-name variable

       If the server successfully updates the client's PTR record, this
       variable will record the name that the DHCP server used for the PTR
       record.   The name to which the PTR record points will be either the
       ddns-fwd-name or the ddns-client-fqdn.

       Executable Statements

       on events { statements... }
       The on statement records a list of statements to execute if a
       certain event occurs.   The possible events that can occur for an
       active lease are release and expiry.   More than one event
       can be specified - if so, the events are separated by '|' characters.

       The authoring-byte-order statement

         authoring-byte-order [ big-endian | little-endian ] ;

         This statement is automatically added to the top of new lease files by
         the server. It indicates the internal byte order of the server.  This
         permits lease files generated on a server with one form of byte order
         to be read by a server with a different form.  Lease files which do not
         contain this entry are simply treated as having the same byte order as
         the server reading them.  If you are migrating lease files generated
         by a server that predates this statement and is of a different byte
         order than the your destination server, you can manually add this
         statement.  It must proceed any lease entries.  Valid values for this
         parameter are little-endian and big-endian.


THE DHCPv4 LEASE DECLARATION
       lease ip-address { statements... }

       Each lease declaration includes the single IP  address  that  has  been
       leased  to  the  client.    The statements within the braces define the
       duration of the lease and to whom it is assigned.

       starts date;
       ends date;
       tstp date;
       tsfp date;
       atsfp date;
       cltt date;

       The start and end time of a lease are recorded  using  the  starts  and
       ends statements.   The tstp statement is present if the failover proto-
       col is being used, and indicates what time the peer has been  told  the
       lease  expires.    The  tsfp  statement is also present if the failover
       protocol is being used, and indicates the lease expiry  time  that  the
       peer  has  acknowledged.   The  atsfp statement is the actual time sent
       from the failover partner.  The cltt statement  is  the  client's  last
       transaction time.

       See the description of dates in the section on common structures.

       hardware hardware-type mac-address;

       The hardware statement records the MAC address of the network interface
       on which the lease will be used.   It is specified as a series of hexa-
       decimal octets, separated by colons.

       uid client-identifier;

       The  uid  statement records the client identifier used by the client to
       acquire the lease.   Clients are not required to  send  client  identi-
       fiers,  and  this statement only appears if the client did in fact send
       one.   Client identifiers are normally an ARP  type  (1  for  ethernet)
       followed  by  the MAC address, just like in the hardware statement, but
       this is not required.

       The client identifier is recorded as a colon-separated hexadecimal list
       or  as  a  quoted string.   If it is recorded as a quoted string and it
       contains one or more non-printable  characters,  those  characters  are
       represented  as octal escapes - a backslash character followed by three
       octal digits.  The format used is  determined  by  the  lease-id-format
       parameter, which defaults to octal.

       client-hostname hostname ;

       Most DHCP clients will send their hostname in the host-name option.  If
       a client sends its hostname in this way, the hostname  is  recorded  on
       the  lease  with a client-hostname statement.   This is not required by
       the protocol, however, so many specialized DHCP clients do not  send  a
       host-name option.

       binding state state;
       next binding state state;

       The  binding  state statement declares the lease's binding state.  When
       the DHCP server is not configured  to  use  the  failover  protocol,  a
       lease's  binding  state may be active, free or abandoned.  The failover
       protocol adds some additional  transitional  states,  as  well  as  the
       backup  state,  which indicates that the lease is available for alloca-
       tion by the failover secondary. Please  see  the  dhcpd.conf(5)  manual
       page for more information about abandoned leases.

       The  next  binding  state statement indicates what state the lease will
       move to when the current state expires.   The  time  when  the  current
       state expires is specified in the ends statement.

       rewind binding state state;

       This  statement is part of an optimization for use with failover.  This
       helps a server rewind a lease to the state most recently transmitted to
       its peer.

       option agent.circuit-id string;
       option agent.remote-id string;

       These  statements  are  used  to  record  the  circuit ID and remote ID
       options sent by the relay agent, if the  relay  agent  uses  the  relay
       agent  information  option.   This allows these options to be used con-
       sistently in conditional evaluations even when the client is contacting
       the server directly rather than through its relay agent.

       The vendor-class-identifier variable

       The  server  retains the client-supplied Vendor Class Identifier option
       for informational  purposes,  and  to  render  them  in  DHCPLEASEQUERY
       responses.

       bootp;
       reserved;

       If  present,  they  indicate that the BOOTP and RESERVED failover flags
       (respectively) should be set.  BOOTP and RESERVED  dynamic  leases  are
       treated  differently  than  normal  dynamic leases, as they may only be
       used by the client to which they are currently allocated.

       Other Additional options or executable statements may be included,  see
       the description of them in the section on common structures.


THE DHCPv6 LEASE (IA) DECLARATION
       ia_ta  IAID_DUID { statements... }
       ia_na  IAID_DUID { statements... }
       ia_pd  IAID_DUID { statements... }

       Each  lease  declaration  starts  with a tag indicating the type of the
       lease.  ia_ta is for temporary addresses, ia_na  is  for  non-temporary
       addresses  and  ia_pd  is for prefix delegation.  Following this tag is
       the combined IAID and DUID from the client for this lease.

       The IAID_DUID value is recorded as a colon-separated  hexadecimal  list
       or  as  a  quoted string.   If it is recorded as a quoted string and it
       contains one or more non-printable  characters,  those  characters  are
       represented  as octal escapes - a backslash character followed by three
       octal digits.  The format  used  is  governed  by  the  lease-id-format
       parameter, which defaults to octal.

       cltt date;

       The cltt statement is the client's last transaction time.

       See the description of dates in the section on common structures.

       iaaddr ipv6-address { statements... }
       iaprefix ipv6-address/prefix-length { statements... }

       Within a given lease there can be multiple iaaddr and iaprefix statements.
       Each will have either an IPv6 address or an IPv6 prefix (an address and
       a prefix length indicating a CIDR style block of addresses).  The following
       statements may occur Within each iaaddr or iaprefix.

       binding state state;

       The binding state statement declares the lease's binding state.
       In DHCPv6 you will normally see this as active or expired.

       preferred-life lifetime;

       The IPv6 preferred lifetime associated with this address, in seconds.

       max-life lifetime;

       The valid lifetime associated with this address, in seconds.

       ends date;

       The end time of the lease.  See the description of dates in the section on
       common structures.

       Additional options or executable statements may be included.  See the description
       of them in the section on common structures.


THE FAILOVER PEER STATE DECLARATION
       The  state of any failover peering arrangements is also recorded in the
       lease file, using the failover peer statement:

       failover peer name state {
       my state state at date;
       peer state state at date;
       }

       The states of the peer named name is being recorded.   Both  the  state
       of  the  running server (my state) and the other failover partner (peer
       state) are recorded.   The  following  states  are  possible:  unknown-
       state,  partner-down,  normal,  communications-interrupted, resolution-
       interrupted,  potential-conflict,  recover,   recover-done,   shutdown,
       paused, and startup.

FILES
       DBDIR/dhcpd.leases DBDIR/dhcpd.leases~

SEE ALSO
       dhcpd(8),   dhcp-options(5),   dhcp-eval(5),   dhcpd.conf(5),  RFC2132,
       RFC2131.

AUTHOR
       dhcpd(8) is maintained by ISC.  Information about Internet Systems Con-
       sortium can be found at: https://www.isc.org/



                                                               dhcpd.leases(5)

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