bionic (5) dhcpd.leases.5.gz

Provided by: isc-dhcp-server_4.3.5-3ubuntu7.4_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)