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/db/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 database is created and all known leases are dumped to it. Then, the old lease database is renamed /var/db/dhcpd.leases~. Finally, the newly written lease database is moved into place.

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 _r_u_b_o_u_t is written to the lease file. This is just the same declaration, with {{ ddeelleetteedd;; }} 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 ddhhccppdd..ccoonnff file; in this case, the rubout can never be eliminated from the ddhhccppdd..lleeaasseess file.

THE LEASE DECLARATION

lease _i_p_-_a_d_d_r_e_s_s {{ _s_t_a_t_e_m_e_n_t_s_._._. }}<> <> EEaacchh lleeaassee ddeeccllaarraattiioonn iinncclluuddeess tthhee ssiinnggllee IIPP aaddddrreessss tthhaatt hhaass bbeeeenn lleeaasseedd ttoo tthhee cclliieenntt.. TThhee ssttaatteemmeennttss wwiitthhiinn tthhee bbrraacceess ddeeffiinnee tthhee dduurraattiioonn ooff tthhee lleeaassee aanndd ttoo wwhhoomm iitt iiss aassssiiggnneedd.. <> <> <> <>ssttaarrttss _d_a_t_e;; ends _d_a_t_e;; tstp _d_a_t_e;; tsfp _d_a_t_e;;

The start and end time of a lease are recorded using the ssttaarrttss and eennddss statements. The ttssttpp statement is specified if the failover protocol is being used, and indicates what time the peer has been told the lease expires. The ttssffpp statement is also specified if the failover protocol is being used, and indicates the lease expiry time that the peer has acknowledged. The _d_a_t_e is specified as follows:

weekday year//_m_o_n_t_h//_d_a_y _h_o_u_r::_m_i_n_u_t_e::_s_e_c_o_n_d

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 Coordinated Universal 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 ddaattee --uu.

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

hardware _h_a_r_d_w_a_r_e_-_t_y_p_e _m_a_c_-_a_d_d_r_e_s_s;;

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 _c_l_i_e_n_t_-_i_d_e_n_t_i_f_i_e_r;;

The uuiidd 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 hhaarrddwwaarree _s_t_a_t_e_m_e_n_t_, _b_u_t _t_h_i_s _i_s _n_o_t _r_e_q_u_i_r_e_d_. _<_p_> _T_h_e _c_l_i_e_n_t _i_d_e_n_t_i_f_i_e_r _i_s _r_e_c_o_r_d_e_d _a_s _a _c_o_l_o_n_-_s_e_p_a_r_a_t_e_d _h_e_x_a_d_e_c_i_m_a_l _l_i_s_t _o_r _a_s _a _q_u_o_t_e_d _s_t_r_i_n_g_. _I_f _i_t _i_s _r_e_c_o_r_d_e_d _a_s _a _q_u_o_t_e_d _s_t_r_i_n_g _a_n_d _i_t _c_o_n_t_a_i_n_s _o_n_e _o_r _m_o_r_e _n_o_n_-_p_r_i_n_t_a_b_l_e _c_h_a_r_a_c_t_e_r_s_, _t_h_o_s_e _c_h_a_r_a_c_t_e_r_s _a_r_e _r_e_p_r_e_s_e_n_t_e_d _a_s _o_c_t_a_l _e_s_c_a_p_e_s _- _a _b_a_c_k_s_l_a_s_h _c_h_a_r_a_c_t_e_r _f_o_l_l_o_w_e_d _b_y _t_h_r_e_e _o_c_t_a_l _d_i_g_i_t_s_. _<_p_> _<_b_>_c_l_i_e_n_t_-_h_o_s_t_n_a_m_e _h_o_s_t_n_a_m_e ;;

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

abandoned;

The aabbaannddoonneedd statement indicates that the DHCP server has abandoned the lease. In that case, the aabbaannddoonneedd statement will be used to indicate that the lease should not be reassigned. Please see the ddhhccppdd..ccoonnff((55)) manual page for information about abandoned leases.

binding state _s_t_a_t_e;;<> <>nneexxtt bbiinnddiinngg ssttaattee _s_t_a_t_e;;<> <> TThhee bbiinnddiinngg ssttaattee statement declares the lease's binding state. When the DHCP server is not configured to use the failover protocol, a lease's binding state will be either aaccttiivvee or ffrreeee. The failover protocol adds some additional transitional states, as well as the bbaacckkuupp state, which indicates that the lease is available for allocation by the failover secondary.

The nneexxtt bbiinnddiinngg ssttaattee 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 _e_n_d_s statement.

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

The ooppttiioonn aaggeenntt..cciirrccuuiitt--iidd and ooppttiioonn aaggeenntt..rreemmoottee--iidd statements are used to record the circuit ID and remote ID options send by the relay agent, if the relay agent uses the _r_e_l_a_y _a_g_e_n_t _i_n_f_o_r_m_a_t_i_o_n _o_p_t_i_o_n. 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.

set _v_a_r_i_a_b_l_e == _v_a_l_u_e;;<> <> TThhee sseett statement sets the value of a variable on the lease. For general information on variables, see the ddhhccpp--eevvaall((55)) manual page.

The _d_d_n_s_-_t_e_x_t vvaarriiaabbllee<> <> TThhee _d_d_n_s_-_t_e_x_t variable is used to record the value of the client's TXT identification record when the interim ddns update style has been used to update the DNS for a particular lease.

The _d_d_n_s_-_f_w_d_-_n_a_m_e vvaarriiaabbllee<> <> TThhee _d_d_n_s_-_f_w_d_-_n_a_m_e vvaarriiaabbllee rreeccoorrddss tthhee vvaalluuee ooff tthhee nnaammee uusseedd iinn uuppddaattiinngg tthhee cclliieenntt''ss AA rreeccoorrdd iiff aa DDDDNNSS uuppddaattee hhaass bbeeeenn ssuucccceessssffuullllyy ddoonnee bbyy tthhee sseerrvveerr.. TThhee sseerrvveerr mmaayy aallssoo hhaavvee uusseedd tthhiiss nnaammee ttoo uuppddaattee tthhee cclliieenntt''ss PPTTRR rreeccoorrdd.. <> <>TThhee _d_d_n_s_-_c_l_i_e_n_t_-_f_q_d_n vvaarriiaabbllee<> <> IIff tthhee sseerrvveerr iiss ccoonnffiigguurreedd ttoo uussee tthhee iinntteerriimm ddddnnss uuppddaattee ssttyyllee,, aanndd iiss aallssoo ccoonnffiigguurreedd ttoo aallllooww cclliieennttss ttoo uuppddaattee tthheeiirr oowwnn ffqqddnnss,, aanndd tthhee cclliieenntt ddiidd iinn ffaacctt uuppddaattee iittss oowwnn ffqqddnn,, tthheenn tthhee _d_d_n_s_-_c_l_i_e_n_t_-_f_q_d_n 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 _d_d_n_s_-_r_e_v_-_n_a_m_e vvaarriiaabbllee<> <> IIff tthhee sseerrvveerr ssuucccceessssffuullllyy uuppddaatteess tthhee cclliieenntt''ss PPTTRR rreeccoorrdd,, tthhiiss vvaarriiaabbllee wwiillll rreeccoorrdd tthhee nnaammee tthhaatt tthhee DDHHCCPP sseerrvveerr uusseedd ffoorr tthhee PPTTRR rreeccoorrdd.. TThhee nnaammee ttoo wwhhiicchh tthhee PPTTRR rreeccoorrdd ppooiinnttss wwiillll bbee eeiitthheerr tthhee _d_d_n_s_-_f_w_d_-_n_a_m_e or the _d_d_n_s_-_c_l_i_e_n_t_-_f_q_d_n.

on _e_v_e_n_t_s {{ _s_t_a_t_e_m_e_n_t_s_._._. }}<> TThhee oonn _s_t_a_t_e_m_e_n_t _r_e_c_o_r_d_s _a _l_i_s_t _o_f _s_t_a_t_e_m_e_n_t_s _t_o _e_x_e_c_u_t_e _i_f _a _c_e_r_t_a_i_n _e_v_e_n_t _o_c_c_u_r_s_. _T_h_e _p_o_s_s_i_b_l_e _e_v_e_n_t_s _t_h_a_t _c_a_n _o_c_c_u_r _f_o_r _a_n _a_c_t_i_v_e _l_e_a_s_e _a_r_e rreelleeaassee and eexxppiirryy. More than one event can be specified - if so, the events are separated by '|' characters.

THE FAILOVER PEER STATE DECLARATION

The state of any failover peering arrangements is also recorded in the lease file, using the ffaaiilloovveerr ppeeeerr statement:


failover peer _n_a_m_e ssttaattee {{<>
<>mmyy ssttaattee _s_t_a_t_e aatt _d_a_t_e;;<>
<>ppeeeerr ssttaattee _s_t_a_t_e aatt _d_a_t_e;;<>
<>}}<>
<>
<>
TThhee ssttaatteess ooff tthhee ppeeeerr nnaammeedd _n_a_m_e is being recorded.   Both the
state of the running server (mmyy ssttaattee) and the other failover
partner (_p_e_e_r _s_t_a_t_e) are recorded.   The following states are
possible: uunnkknnoowwnn--ssttaattee, ppaarrttnneerr--ddoowwnn, nnoorrmmaall,
ccoommmmuunniiccaattiioonnss--iinntteerrrruupptteedd, rreessoolluuttiioonn--iinntteerrrruupptteedd,
ppootteennttiiaall--ccoonnfflliicctt, rreeccoovveerr, rreeccoovveerr--ddoonnee,
sshhuuttddoowwnn, ppaauusseedd, and ssttaarrttuupp.
DBDIR/dhcpd.leases

SEE ALSO

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

AUTHOR

dhcpd(8) was written by Ted Lemon under a contract with Vixie Labs. Funding for this project was provided by Internet Systems Consortium. Information about Internet Systems Consortium can be found at: http://www.isc.org/