Provided by: isc-dhcp-server_4.4.1-2.1ubuntu9_amd64 bug

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 /var/lib/dhcp/dhcpd.leases.   You can do this with:

            touch /var/lib/dhcp/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 database is created and all known leases are
       dumped  to  it.    Then,  the  old  lease database is renamed /var/lib/dhcp/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  declaration, 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 protocol 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 general 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 protocol 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 hexadecimal 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 identifiers, 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  allocation  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  consistently  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

       /var/lib/dhcp/dhcpd.leases /var/lib/dhcp/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 Consortium can be found
       at: https://www.isc.org/

                                                                                  dhcpd.leases(5)