server/dhcpd.leases.5

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  24 .\" $Id: dhcpd.leases.5,v 1.17 2011/09/19 00:24:50 sar Exp $
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  26 .TH dhcpd.leases 5
  27 .SH NAME
  28 dhcpd.leases - DHCP client lease database
  29 .SH DESCRIPTION
  30 The Internet Systems Consortium DHCP Server keeps a persistent
  31 database of leases that it has assigned.  This database is a free-form
  32 ASCII file containing a series of lease declarations.  Every time a
  33 lease is acquired, renewed or released, its new value is recorded at
  34 the end of the lease file.  So if more than one declaration appears
  35 for a given lease, the last one in the file is the current one.
  36 .PP
  37 When dhcpd is first installed, there is no lease database.   However,
  38 dhcpd requires that a lease database be present before it will start.
  39 To make the initial lease database, just create an empty file called
  40 DBDIR/dhcpd.leases.   You can do this with:
  41 .PP
  42 .nf
  43         touch DBDIR/dhcpd.leases
  44 .fi
  45 .PP
  46 In order to prevent the lease database from growing without bound, the
  47 file is rewritten from time to time.   First, a temporary lease
  48 database is created and all known leases are dumped to it.   Then, the
  49 old lease database is renamed DBDIR/dhcpd.leases~.   Finally, the
  50 newly written lease database is moved into place.
  51 .PP
  52 In order to process both DHCPv4 and DHCPv6 messages you will need to
  53 run two separate instances of the dhcpd process.  Each of these
  54 instances will need it's own lease file.  You can use the \fI-lf\fR
  55 option on the server's command line to specify a different lease file
  56 name for one or both servers.
  57 .SH FORMAT
  58 Lease descriptions are stored in a format that is parsed by the same
  59 recursive descent parser used to read the
  60 .B dhcpd.conf(5)
  61 and
  62 .B dhclient.conf(5)
  63 files.  Lease files can contain lease declarations, and also group and
  64 subgroup declarations, host declarations and failover state
  65 declarations.  Group, subgroup and host declarations are used to
  66 record objects created using the OMAPI protocol.
  67 .PP
  68 The lease file is a log-structured file - whenever a lease changes,
  69 the contents of that lease are written to the end of the file.   This
  70 means that it is entirely possible and quite reasonable for there to
  71 be two or more declarations of the same lease in the lease file at the
  72 same time.   In that case, the instance of that particular lease that
  73 appears last in the file is the one that is in effect.
  74 .PP
  75 Group, subgroup and host declarations in the lease file are handled in
  76 the same manner, except that if any of these objects are deleted, a
  77 \fIrubout\fR is written to the lease file.   This is just the same
  78 declaration, with \fB{ deleted; }\fR in the scope of the
  79 declaration.   When the lease file is rewritten, any such rubouts that
  80 can be eliminated are eliminated.   It is possible to delete a
  81 declaration in the \fBdhcpd.conf\fR file; in this case, the rubout
  82 can never be eliminated from the \fBdhcpd.leases\fR file.
  83 .SH COMMON STATEMENTS FOR LEASE DECLARATIONS
  84 While the lease file formats for DHCPv4 and DHCPv6 are different
  85 they share many common statements and structures.  This section
  86 describes the common statements while the succeeding sections
  87 describe the protocol specific statements.
  88 .PP
  89 .B Dates
  90 .PP
  91 A \fIdate\fR is specified in two ways, depending on the configuration
  92 value for the \fBdb-time-format\fR parameter.  If it was set to \fIdefault\fR,
  93 then the \fIdate\fR fields appear as follows:
  94 .PP
  95 .I weekday year\fB/\fImonth\fB/\fIday hour\fB:\fIminute\fB:\fIsecond\fR
  96 .PP
  97 The weekday is present to make it easy for a human to tell when a
  98 lease expires - it's specified as a number from zero to six, with zero
  99 being Sunday.  The day of week is ignored on input.  The year is
 100 specified with the century, so it should generally be four digits
 101 except for really long leases.  The month is specified as a number
 102 starting with 1 for January.  The day of the month is likewise
 103 specified starting with 1.  The hour is a number between 0 and 23, the
 104 minute a number between 0 and 59, and the second also a number between
 105 0 and 59.
 106 .PP
 107 Lease times are specified in Universal Coordinated Time (UTC), not in
 108 the local time zone.  There is probably nowhere in the world where the
 109 times recorded on a lease are always the same as wall clock times.  On
 110 most unix machines, you can display the current time in UTC by typing
 111 \fBdate -u\fR.
 112 .PP
 113 If the \fBdb-time-format\fR was configured to \fIlocal\fR, then
 114 the \fIdate\fR fields appear as follows:
 115 .PP
 116  \fBepoch\fR \fI<seconds-since-epoch>\fR\fB; #\fR \fI<day-name> <month-name>
 117 <day-number> <hours>\fR\fB:\fR\fI<minutes>\fR\fB:\fR\fI<seconds> <year>\fR
 118 .PP
 119 The \fIseconds-since-epoch\fR is as according to the system's local clock (often
 120 referred to as "unix time").  The \fB#\fR symbol supplies a comment that
 121 describes what actual time this is as according to the system's configured
 122 timezone, at the time the value was written.  It is provided only for human
 123 inspection.
 124 .PP
 125 If a lease will never expire, \fIdate\fR is \fBnever\fR instead of an
 126 actual date.
 127 .PP
 128 .B General Variables
 129 .PP
 130 As part of the processing of a lease information may be attached to the
 131 lease structure, for example the DDNS information or if you specify a
 132 variable in your configuration file.  Some of these, like the DDNS
 133 information, have specific descriptions below.  For others, such as
 134 any you might define, a generic line of the following will be included.
 135 .PP
 136 .B set \fIvariable\fB = \fIvalue\fB;
 137 .PP
 138 The \fBset\fR statement sets the value of a variable on the lease.
 139 For general information on variables, see the \fBdhcp-eval(5)\fR
 140 manual page.
 141 .PP
 142 .B DDNS Variables
 143 .PP
 144 .nf
 145 .B The \fIddns-text\fB and \fIddns-dhcid\fB variables
 146 .PP
 147 These variables are used to record the value of the client's identification
 148 record when the server has updated DNS for a particular lease.  The text
 149 record is used with the interim DDNS update style while the dhcid record
 150 is used for the standard DDNS update style.
 151 .PP
 152 .B The \fIddns-fwd-name\fB variable
 153 .PP
 154 This variable records the value of the name used in
 155 updating the client's A record if a DDNS update has been successfully
 156 done by the server.   The server may also have used this name to
 157 update the client's PTR record.
 158 .PP
 159 .B The \fIddns-client-fqdn\fB variable
 160 .PP
 161 If the server is configured both to use the interim or standard DDNS update
 162 style, and to allow clients to update their own FQDNs, then if the
 163 client did in fact update its own FQDN, the
 164 \fIddns-client-fqdn\fR variable records the name that the client has
 165 indicated it is using.   This is the name that the server will have
 166 used to update the client's PTR record in this case.
 167 .PP
 168 .B The \fIddns-rev-name\fB variable
 169 .PP
 170 If the server successfully updates the client's PTR record, this
 171 variable will record the name that the DHCP server used for the PTR
 172 record.   The name to which the PTR record points will be either the
 173 \fIddns-fwd-name\fR or the \fIddns-client-fqdn\fR.
 174 .PP
 175 .B Executable Statements
 176 .PP
 177 .B on \fIevents\fB { \fIstatements...\fB }
 178 The \fBon\fR statement records a list of statements to execute if a
 179 certain event occurs.   The possible events that can occur for an
 180 active lease are \fBrelease\fR and \fBexpiry\fR.   More than one event
 181 can be specified - if so, the events are separated by '|' characters.
 182 .PP
 183 The \fIauthoring-byte-order\fR statement
 184 .RS 0.25i
 185 .PP
 186 .B authoring-byte-order \fR[ \fIbig-endian\fR | \fIlittle-endian\fR ] \fB;\fR
 187 .PP
 188 This statement is automatically added to the top of new lease files by
 189 the server. It indicates the internal byte order of the server.  This
 190 permits lease files generated on a server with one form of byte order
 191 to be read by a server with a different form.  Lease files which do not
 192 contain this entry are simply treated as having the same byte order as
 193 the server reading them.  If you are migrating lease files generated
 194 by a server that predates this statement and is of a different byte
 195 order than the your destination server, you can manually add this
 196 statement.  It must proceed any lease entries.  Valid values for this
 197 parameter are \fIlittle-endian\fR and \fIbig-endian\fR.
 198 .RE
 199 .PP
 200 .SH THE DHCPv4 LEASE DECLARATION
 201 .PP
 202 .B lease \fIip-address\fB { \fIstatements...\fB }
 203 .PP
 204 Each lease declaration includes the single IP address that has been
 205 leased to the client.   The statements within the braces define the
 206 duration of the lease and to whom it is assigned.
 207 .PP
 208 .nf
 209 .B starts \fIdate\fB;\fR
 210 .B ends \fIdate\fB;\fR
 211 .B tstp \fIdate\fB;\fR
 212 .B tsfp \fIdate\fB;\fR
 213 .B atsfp \fIdate\fB;\fR
 214 .B cltt \fIdate\fB;\fR
 215 .fi
 216 .PP
 217 The start and end time of a lease are recorded using the \fBstarts\fR
 218 and \fBends\fR statements.   The \fBtstp\fR statement is present if
 219 the failover protocol is being used, and indicates what time the peer
 220 has been told the lease expires.   The \fBtsfp\fR statement is
 221 also present if the failover protocol is being used, and indicates
 222 the lease expiry time that the peer has acknowledged.
 223 The \fBatsfp\fR statement is the actual time sent from the failover
 224 partner.
 225 The \fBcltt\fR statement is the client's last transaction time.
 226 .PP
 227 See the description of dates in the section on common structures.
 228 .PP
 229 .B hardware \fIhardware-type mac-address\fB;\fR
 230 .PP
 231 The hardware statement records the MAC address of the network
 232 interface on which the lease will be used.   It is specified as a
 233 series of hexadecimal octets, separated by colons.
 234 .PP
 235 .B uid \fIclient-identifier\fB;\fR
 236 .PP
 237 The \fBuid\fR statement records the client identifier used by the
 238 client to acquire the lease.   Clients are not required to send client
 239 identifiers, and this statement only appears if the client did in fact
 240 send one.   Client identifiers are normally an ARP type (1 for
 241 ethernet) followed by the MAC address, just like in the \fBhardware\fI
 242 statement, but this is not required.
 243 .PP
 244 The client identifier is recorded as a colon-separated hexadecimal
 245 list or as a quoted string.   If it is recorded as a quoted string and
 246 it contains one or more non-printable characters, those characters are
 247 represented as octal escapes - a backslash character followed by three
 248 octal digits.  The format used is determined by the lease-id-format
 249 parameter, which defaults to octal.
 250 .PP
 251 .B client-hostname "\fIhostname\fB";\fR
 252 .PP
 253 Most DHCP clients will send their hostname in the \fIhost-name\fR
 254 option.  If a client sends its hostname in this way, the hostname is
 255 recorded on the lease with a \fBclient-hostname\fR statement.   This
 256 is not required by the protocol, however, so many specialized DHCP
 257 clients do not send a host-name option.
 258 .PP
 259 .nf
 260 .B binding state \fIstate\fB;
 261 .B next binding state \fIstate\fB;
 262 .fi
 263 .PP
 264 The \fBbinding state\fR statement declares the lease's binding state.
 265 When the DHCP server is not configured to use the failover protocol, a
 266 lease's binding state may be \fBactive\fR, \fBfree\fR or \fBabandoned\fR.
 267 The failover protocol adds some additional transitional states, as well as
 268 the \fBbackup\fR state, which indicates that the lease is available
 269 for allocation by the failover secondary. Please see the \fBdhcpd.conf(5)\fR
 270 manual page for more information about abandoned leases.
 271 .PP
 272 The \fBnext binding state\fR statement indicates what state the lease
 273 will move to when the current state expires.   The time when the
 274 current state expires is specified in the \fIends\fR statement.
 275 .PP
 276 .B rewind binding state \fIstate\fB;
 277 .PP
 278 This statement is part of an optimization for
 279 use with failover.  This helps a server rewind a lease to the state most
 280 recently transmitted to its peer.
 281 .PP
 282 .nf
 283 .B option agent.circuit-id \fIstring\fR;
 284 .B option agent.remote-id \fIstring\fR;
 285 .fi
 286 .PP
 287 These statements are used to record the circuit ID and remote ID options
 288 sent by the relay agent, if the relay agent uses the \fIrelay agent
 289 information option\fR.   This allows these options to be used
 290 consistently in conditional evaluations even when the client is
 291 contacting the server directly rather than through its relay agent.
 292 .PP
 293 .B The \fIvendor-class-identifier\fB variable
 294 .PP
 295 The server retains the client-supplied Vendor Class Identifier option
 296 for informational purposes, and to render them in DHCPLEASEQUERY responses.
 297 .PP
 298 .nf
 299 .B bootp;
 300 .B reserved;
 301 .fi
 302 .PP
 303 If present, they indicate that the BOOTP and RESERVED failover flags
 304 (respectively) should be set.  BOOTP
 305 and RESERVED dynamic leases are treated differently than normal dynamic leases,
 306 as they may only be used by the client to which they are currently allocated.
 307 .PP
 308 .B Other
 309 Additional options or executable statements may be included, see the description
 310 of them in the section on common structures.
 311 .RE
 312 .PP
 313 .SH THE DHCPv6 LEASE (IA) DECLARATION
 314 .PP
 315 .nf
 316 .B ia_ta \fI IAID_DUID\fB { \fIstatements...\fB }
 317 .B ia_na \fI IAID_DUID\fB { \fIstatements...\fB }
 318 .B ia_pd \fI IAID_DUID\fB { \fIstatements...\fB }
 319 .fi
 320 .PP
 321 Each lease declaration starts with a tag indicating the type of the lease.
 322 ia_ta is for temporary addresses, ia_na is for non-temporary addresses and
 323 ia_pd is for prefix delegation.  Following this tag is the combined IAID
 324 and DUID from the client for this lease.
 325 .PP
 326 The IAID_DUID value is recorded as a colon-separated hexadecimal
 327 list or as a quoted string.   If it is recorded as a quoted string and
 328 it contains one or more non-printable characters, those characters are
 329 represented as octal escapes - a backslash character followed by three
 330 octal digits.  The format used is governed by the lease-id-format parameter,
 331 which defaults to octal.
 332 .PP
 333 .B cltt \fIdate\fB;\fR
 334 .PP
 335 The \fBcltt\fR statement is the client's last transaction time.
 336 .PP
 337 See the description of dates in the section on common structures.
 338 .PP
 339 .nf
 340 .B iaaddr \fIipv6-address\fB { \fIstatements...\fB }
 341 .B iaprefix \fIipv6-address/prefix-length\fB { \fIstatements...\fB }
 342 .PP
 343 Within a given lease there can be multiple iaaddr and iaprefix statements.
 344 Each will have either an IPv6 address or an IPv6 prefix (an address and
 345 a prefix length indicating a CIDR style block of addresses).  The following
 346 statements may occur Within each iaaddr or iaprefix.
 347 .PP
 348 .B binding state \fIstate\fB;
 349 .PP
 350 The \fBbinding state\fR statement declares the lease's binding state.
 351 In DHCPv6 you will normally see this as \fIactive\fR or \fIexpired\fR.
 352 .PP
 353 .B  preferred-life \fIlifetime\fB;
 354 .PP
 355 The IPv6 preferred lifetime associated with this address, in seconds.
 356 .PP
 357 .B max-life \fIlifetime\fB;
 358 .PP
 359 The valid lifetime associated with this address, in seconds.
 360 .PP
 361 .B ends \fIdate\fB;\fR
 362 .PP
 363 The end time of the lease.  See the description of dates in the section on
 364 common structures.
 365 .PP
 366 Additional options or executable statements may be included.  See the description
 367 of them in the section on common structures.
 368 .PP
 369 .RE
 370 .SH THE FAILOVER PEER STATE DECLARATION
 371 The state of any failover peering arrangements is also recorded in the
 372 lease file, using the \fBfailover peer\fR statement:
 373 .PP
 374 .nf
 375 .B failover peer "\fIname\fB" state {
 376 .B   my   state \fIstate\fB at \fIdate\fB;
 377 .B   peer state \fIstate\fB at \fIdate\fB;
 378 .B }
 379 .fi
 380 .PP
 381 The states of the peer named \fIname\fR is being recorded.   Both the
 382 state of the running server (\fBmy state\fR) and the other failover
 383 partner (\fIpeer state\fR) are recorded.   The following states are
 384 possible: \fBunknown-state\fR, \fBpartner-down\fR, \fBnormal\fR,
 385 \fBcommunications-interrupted\fR, \fBresolution-interrupted\fR,
 386 \fBpotential-conflict\fR, \fBrecover\fR, \fBrecover-done\fR,
 387 \fBshutdown\fR, \fBpaused\fR, and \fBstartup\fR.
 388 .RE
 389 .SH FILES
 390 .B DBDIR/dhcpd.leases DBDIR/dhcpd.leases~
 391 .SH SEE ALSO
 392 dhcpd(8), dhcp-options(5), dhcp-eval(5), dhcpd.conf(5), RFC2132, RFC2131.
 393 .SH AUTHOR
 394 .B dhcpd(8)
 395 is maintained by ISC.
 396 Information about Internet Systems Consortium can be found at:
 397 .B https://www.isc.org/