Remove dhcp-3.0 from base and import dhclient from OpenBSD. Porting work
[dragonfly.git] / sbin / dhclient / dhclient.conf.5
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1.\" $OpenBSD: dhclient.conf.5,v 1.14 2007/10/16 05:03:23 jmc Exp $
2.\" $DragonFly: src/sbin/dhclient/dhclient.conf.5,v 1.1 2008/08/30 16:07:58 hasso Exp $
3.\"
4.\" Copyright (c) 1997 The Internet Software Consortium.
5.\" All rights reserved.
6.\"
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8.\" modification, are permitted provided that the following conditions
9.\" are met:
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13.\" 2. Redistributions in binary form must reproduce the above copyright
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15.\" documentation and/or other materials provided with the distribution.
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20.\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
21.\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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34.\" This software has been written for the Internet Software Consortium
35.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
36.\" Enterprises. To learn more about the Internet Software Consortium,
37.\" see ``http://www.isc.org/isc''. To learn more about Vixie
38.\" Enterprises, see ``http://www.vix.com''.
39.\"
40.Dd $Mdocdate$
41.Dt DHCLIENT.CONF 5
42.Os
43.Sh NAME
44.Nm dhclient.conf
45.Nd DHCP client configuration file
46.Sh DESCRIPTION
47The
48.Nm
49file contains configuration information for
50.Xr dhclient 8 ,
51the Internet Software Consortium DHCP Client.
52.Pp
53The
54.Nm
55file is a free-form ASCII text file.
56It is parsed by the recursive-descent parser built into
57.Xr dhclient 8 .
58The file may contain extra tabs and newlines for formatting purposes.
59Keywords in the file are case-insensitive.
60Comments may be placed anywhere within the file (except within quotes).
61Comments begin with the
62.Sq #
63character and end at the end of the line.
64.Pp
65The
66.Nm
67file can be used to configure the behaviour of the client in a wide variety
68of ways: protocol timing, information requested from the server, information
69required of the server, defaults to use if the server does not provide
70certain information, values with which to override information provided by
71the server, or values to prepend or append to information provided by the
72server.
73The configuration file can also be preinitialized with addresses to
74use on networks that don't have DHCP servers.
75.Sh PROTOCOL TIMING
76The timing behaviour of the client need not be configured by the user.
77If no timing configuration is provided by the user, a fairly
78reasonable timing behaviour will be used by default \- one which
79results in fairly timely updates without placing an inordinate load on
80the server.
81.Pp
82The following statements can be used to adjust the timing behaviour of
83the DHCP client if required, however:
84.Bl -tag -width Ds
85.It Ic timeout Ar time ;
86The
87.Ic timeout
88statement determines the amount of time that must pass between the
89time that the client begins to try to determine its address and the
90time that it decides that it's not going to be able to contact a server.
91By default, this timeout is sixty seconds.
92After the timeout has passed, if there are any static leases defined in the
93configuration file, or any leases remaining in the lease database that
94have not yet expired, the client will loop through these leases
95attempting to validate them, and if it finds one that appears to be
96valid, it will use that lease's address.
97If there are no valid static leases or unexpired leases in the lease database,
98the client will restart the protocol after the defined retry interval.
99.It Ic retry Ar time ;
100The
101.Ic retry
102statement determines the time that must pass after the client has
103determined that there is no DHCP server present before it tries again
104to contact a DHCP server.
105By default, this is five minutes.
106.It Ic select-timeout Ar time ;
107It is possible (some might say desirable) for there to be more than
108one DHCP server serving any given network.
109In this case, it is possible that a client may be sent more than one offer
110in response to its initial lease discovery message.
111It may be that one of these offers is preferable to the other
112(e.g., one offer may have the address the client previously used,
113and the other may not).
114.Pp
115The
116.Ic select-timeout
117is the time after the client sends its first lease discovery request
118at which it stops waiting for offers from servers, assuming that it
119has received at least one such offer.
120If no offers have been received by the time the
121.Ic select-timeout
122has expired, the client will accept the first offer that arrives.
123.Pp
124By default, the
125.Ic select-timeout
126is zero seconds \- that is, the client will take the first offer it sees.
127.It Ic reboot Ar time ;
128When the client is restarted, it first tries to reacquire the last
129address it had.
130This is called the INIT-REBOOT state.
131If it is still attached to the same network it was attached to when it last
132ran, this is the quickest way to get started.
133The
134.Ic reboot
135statement sets the time that must elapse after the client first tries
136to reacquire its old address before it gives up and tries to discover
137a new address.
138By default, the reboot timeout is ten seconds.
139.It Ic backoff-cutoff Ar time ;
140The client uses an exponential backoff algorithm with some randomness,
141so that if many clients try to configure themselves at the same time,
142they will not make their requests in lockstep.
143The
144.Ic backoff-cutoff
145statement determines the maximum amount of time that the client is
146allowed to back off.
147It defaults to 15 seconds.
148.It Ic initial-interval Ar time ;
149The
150.Ic initial-interval
151statement sets the amount of time between the first attempt to reach a
152server and the second attempt to reach a server.
153Each time a message is sent, the interval between messages is incremented by
154twice the current interval multiplied by a random number between zero and one.
155If it is greater than the backoff-cutoff amount, it is set to that
156amount.
157It defaults to ten seconds.
158.It Ic link-timeout Ar time ;
159The
160.Ic link-timeout
161statement sets the amount of time to wait for an interface link before timing
162out.
163The default value is 10 seconds, but the special value 0 requests that dhclient
164not wait for a link state change before timing out.
165.El
166.Sh LEASE REQUIREMENTS AND REQUESTS
167The DHCP protocol allows the client to request that the server send it
168specific information, and not send it other information that it is not
169prepared to accept.
170The protocol also allows the client to reject offers from servers if they
171don't contain information the client needs, or if the information provided
172is not satisfactory.
173.Pp
174There is a variety of data contained in offers that DHCP servers send
175to DHCP clients.
176The data that can be specifically requested is what are called
177.Em DHCP Options .
178DHCP Options are defined in
179.Xr dhcp-options 5 .
180.Bl -tag -width Ds
181.It Xo
182.Ic request Op Ar option
183.Oo , Ar ... option Oc ;
184.Xc
185The
186.Ic request
187statement causes the client to request that any server responding to the
188client send the client its values for the specified options.
189Only the option names should be specified in the request statement \- not
190option parameters.
191.It Xo
192.Ic require Op Ar option
193.Oo , Ar ... option Oc ;
194.Xc
195The
196.Ic require
197statement lists options that must be sent in order for an offer to be accepted.
198Offers that do not contain all the listed options will be ignored.
199.It Xo
200.Ic send No { Op Ar option declaration
201.Oo , Ar ... option declaration Oc }
202.Xc
203The
204.Ic send
205statement causes the client to send the specified options to the server with
206the specified values.
207These are full option declarations as described in
208.Xr dhcp-options 5 .
209Options that are always sent in the DHCP protocol should not be specified
210here.
211One use for this statement is to send information to the server
212that will allow it to differentiate between this client and other
213clients or kinds of clients.
214.El
215.Sh OPTION MODIFIERS
216In some cases, a client may receive option data from the server which
217is not really appropriate for that client, or may not receive
218information that it needs, and for which a useful default value exists.
219It may also receive information which is useful, but which needs to be
220supplemented with local information.
221To handle these needs, several option modifiers are available.
222.Bl -tag -width Ds
223.It Xo
224.Ic default No { Op Ar option declaration
225.Oo , Ar ... option declaration Oc }
226.Xc
227If for some set of options the client should use the value supplied by
228the server, but needs to use some default value if no value was supplied
229by the server, these values can be defined in the
230.Ic default
231statement.
232.It Xo
233.Ic supersede No { Op Ar option declaration
234.Oo , Ar ... option declaration Oc }
235.Xc
236If for some set of options the client should always use its own value
237rather than any value supplied by the server, these values can be defined
238in the
239.Ic supersede
240statement.
241.It Xo
242.Ic prepend No { Op Ar option declaration
243.Oo , Ar ... option declaration Oc }
244.Xc
245If for some set of options the client should use a value you supply,
246and then use the values supplied by the server, if any,
247these values can be defined in the
248.Ic prepend
249statement.
250The
251.Ic prepend
252statement can only be used for options which allow more than one value to
253be given.
254This restriction is not enforced \- if violated, the results are unpredictable.
255.It Xo
256.Ic append No { Op Ar option declaration
257.Oo , Ar ... option declaration Oc }
258.Xc
259If for some set of options the client should first use the values
260supplied by the server, if any, and then use values you supply, these
261values can be defined in the
262.Ic append
263statement.
264The
265.Ic append
266statement can only be used for options which allow more than one value to
267be given.
268This restriction is not enforced \- if you ignore it,
269the behaviour will be unpredictable.
270.El
271.Sh LEASE DECLARATIONS
272The lease declaration:
273.Pp
274.Xo
275.Ic \ \& lease No { Ar lease-declaration
276.Oo Ar ... lease-declaration Oc }
277.Xc
278.Pp
279The DHCP client may decide after some period of time (see
280.Sx PROTOCOL TIMING )
281that it is not going to succeed in contacting a server.
282At that time, it consults its own database of old leases and tests each one
283that has not yet timed out by pinging the listed router for that lease to
284see if that lease could work.
285It is possible to define one or more
286.Em fixed
287leases in the client configuration file for networks where there is no DHCP
288or BOOTP service, so that the client can still automatically configure its
289address.
290This is done with the
291.Ic lease
292statement.
293.Pp
294NOTE: the lease statement is also used in the
295.Pa dhclient.leases
296file in order to record leases that have been received from DHCP servers.
297Some of the syntax for leases as described below is only needed in the
298.Pa dhclient.leases
299file.
300Such syntax is documented here for completeness.
301.Pp
302A lease statement consists of the lease keyword, followed by a left
303curly brace, followed by one or more lease declaration statements,
304followed by a right curly brace.
305The following lease declarations are possible:
306.Bl -tag -width Ds
307.It Ic bootp ;
308The
309.Ic bootp
310statement is used to indicate that the lease was acquired using the
311BOOTP protocol rather than the DHCP protocol.
312It is never necessary to specify this in the client configuration file.
313The client uses this syntax in its lease database file.
314.It Ic interface Ar \&"string\&" ;
315The
316.Ic interface
317lease statement is used to indicate the interface on which the lease is valid.
318If set, this lease will only be tried on a particular interface.
319When the client receives a lease from a server, it always records the
320interface number on which it received that lease.
321If predefined leases are specified in the
322.Nm
323file, the interface should also be specified, although this is not required.
324.It Ic fixed-address Ar ip-address ;
325The
326.Ic fixed-address
327statement is used to set the IP address of a particular lease.
328This is required for all lease statements.
329The IP address must be specified as a dotted quad (e.g., 12.34.56.78).
330.It Ic filename Ar \&"string\&" ;
331The
332.Ic filename
333statement specifies the name of the boot filename to use.
334This is not used by the standard client configuration script, but is
335included for completeness.
336.It Ic server-name Ar \&"string\&" ;
337The
338.Ic server-name
339statement specifies the name of the boot server name to use.
340This is also not used by the standard client configuration script.
341.It Ic option Ar option-declaration ;
342The
343.Ic option
344statement is used to specify the value of an option supplied by the server,
345or, in the case of predefined leases declared in
346.Nm dhclient.conf ,
347the value that the user wishes the client configuration script to use if the
348predefined lease is used.
349.It Ic medium Ar \&"media setup\&" ;
350The
351.Ic medium
352statement can be used on systems where network interfaces cannot
353automatically determine the type of network to which they are connected.
354The media setup string is a system-dependent parameter which is passed
355to the DHCP client configuration script when initializing the interface.
356On
357.Ux
358and UNIX-like systems, the argument is passed on the ifconfig command line
359when configuring the interface.
360.Pp
361The DHCP client automatically declares this parameter if it used a
362media type (see the
363.Ic media
364statement) when configuring the interface in order to obtain a lease.
365This statement should be used in predefined leases only if the network
366interface requires media type configuration.
367.It Ic renew Ar date ;
368.It Ic rebind Ar date ;
369.It Ic expire Ar date ;
370The
371.Ic renew
372statement defines the time at which the DHCP client should begin trying to
373contact its server to renew a lease that it is using.
374The
375.Ic rebind
376statement defines the time at which the DHCP client should begin to try to
377contact
378.Em any
379DHCP server in order to renew its lease.
380The
381.Ic expire
382statement defines the time at which the DHCP client must stop using a lease
383if it has not been able to contact a server in order to renew it.
384.El
385.Pp
386These declarations are automatically set in leases acquired by the
387DHCP client, but must also be configured in predefined leases \- a
388predefined lease whose expiry time has passed will not be used by the
389DHCP client.
390.Pp
391Dates are specified as follows:
392.Pp
393.Ar \ \&<weekday>
394.Sm off
395.Ar <year> No / Ar <month> No / Ar <day>
396.Ar <hour> : <minute> : <second>
397.Sm on
398.Pp
399The weekday is present to make it easy for a human to tell when a
400lease expires \- it's specified as a number from zero to six, with zero
401being Sunday.
402When declaring a predefined lease, it can always be specified as zero.
403The year is specified with the century, so it should generally be four
404digits except for really long leases.
405The month is specified as a number starting with 1 for January.
406The day of the month is likewise specified starting with 1.
407The hour is a number between 0 and 23,
408the minute a number between 0 and 59,
409and the second also a number between 0 and 59.
410.Sh ALIAS DECLARATIONS
411.Ic alias No { Ar declarations ... No }
412.Pp
413Some DHCP clients running TCP/IP roaming protocols may require that in
414addition to the lease they may acquire via DHCP, their interface also
415be configured with a predefined IP alias so that they can have a
416permanent IP address even while roaming.
417The Internet Software Consortium DHCP client doesn't support roaming with
418fixed addresses directly, but in order to facilitate such experimentation,
419the DHCP client can be set up to configure an IP alias using the
420.Ic alias
421declaration.
422.Pp
423The
424.Ic alias
425declaration resembles a lease declaration, except that options other than
426the subnet-mask option are ignored by the standard client configuration
427script, and expiry times are ignored.
428A typical alias declaration includes an interface declaration, a fixed-address
429declaration for the IP alias address, and a subnet-mask option declaration.
430A medium statement should never be included in an alias declaration.
431.Sh OTHER DECLARATIONS
432.Bl -tag -width Ds
433.It Ic reject Ar ip-address ;
434The
435.Ic reject
436statement causes the DHCP client to reject offers from servers who use
437the specified address as a server identifier.
438This can be used to avoid being configured by rogue or misconfigured DHCP
439servers, although it should be a last resort \- better to track down
440the bad DHCP server and fix it.
441.It Xo
442.Ic interface Ar \&"name\&" No { Ar declarations
443.Ar ... No }
444.Xc
445A client with more than one network interface may require different
446behaviour depending on which interface is being configured.
447All timing parameters and declarations other than lease and alias
448declarations can be enclosed in an interface declaration, and those
449parameters will then be used only for the interface that matches the
450specified name.
451Interfaces for which there is no interface declaration will use the
452parameters declared outside of any interface declaration,
453or the default settings.
454.It Xo
455.Ic media Ar \&"media setup\&"
456.Oo , Ar \&"media setup\&" , ... Oc ;
457.Xc
458The
459.Ic media
460statement defines one or more media configuration parameters which may
461be tried while attempting to acquire an IP address.
462The DHCP client will cycle through each media setup string on the list,
463configuring the interface using that setup and attempting to boot,
464and then trying the next one.
465This can be used for network interfaces which aren't capable of sensing
466the media type unaided \- whichever media type succeeds in getting a request
467to the server and hearing the reply is probably right (no guarantees).
468.Pp
469The media setup is only used for the initial phase of address
470acquisition (the DHCPDISCOVER and DHCPOFFER packets).
471Once an address has been acquired, the DHCP client will record it in its
472lease database and will record the media type used to acquire the address.
473Whenever the client tries to renew the lease, it will use that same media type.
474The lease must expire before the client will go back to cycling through media
475types.
476.It Ic script Ar \&"script-name\&" ;
477The
478.Ic script
479statement is used to specify the pathname of the DHCP client configuration
480script.
481This script is used by the DHCP client to set each interface's initial
482configuration prior to requesting an address, to test the address once it
483has been offered, and to set the interface's final configuration once a
484lease has been acquired.
485If no lease is acquired, the script is used to test predefined leases, if
486any, and also called once if no valid lease can be identified.
487For more information, see
488.Xr dhclient.leases 5 .
489.El
490.Sh EXAMPLES
491The following configuration file is used on a laptop
492which has an IP alias of 192.5.5.213, and has one interface,
493ep0 (a 3Com 3C589C).
494Booting intervals have been shortened somewhat from the default, because
495the client is known to spend most of its time on networks with little DHCP
496activity.
497The laptop does roam to multiple networks.
498.Bd -literal -offset indent
499timeout 60;
500retry 60;
501reboot 10;
502select-timeout 5;
503initial-interval 2;
504reject 192.33.137.209;
505
506interface "ep0" {
507 send host-name "andare.fugue.com";
508 send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;
509 send dhcp-lease-time 3600;
510 supersede domain-name "fugue.com rc.vix.com home.vix.com";
511 prepend domain-name-servers 127.0.0.1;
512 request subnet-mask, broadcast-address, time-offset, routers,
513 domain-name, domain-name-servers, host-name;
514 require subnet-mask, domain-name-servers;
515 script "/etc/dhclient-script";
516 media "media 10baseT/UTP", "media 10base2/BNC";
517}
518
519alias {
520 interface "ep0";
521 fixed-address 192.5.5.213;
522 option subnet-mask 255.255.255.255;
523}
524.Ed
525.Pp
526This is a very complicated
527.Nm
528file \- in general, yours should be much simpler.
529In many cases, it's sufficient to just create an empty
530.Nm
531file \- the defaults are usually fine.
532.Sh SEE ALSO
533.Xr dhclient.leases 5 ,
534.Xr dhcp-options 5 ,
535.Xr dhcpd.conf 5 ,
536.Xr dhclient 8 ,
537.Xr dhcpd 8
538.Pp
539RFC 2132, RFC 2131.
540.Sh AUTHORS
541.An -nosplit
542.Xr dhclient 8
543was written by
544.An Ted Lemon Aq mellon@vix.com
545under a contract with Vixie Labs.
546.Pp
547The current implementation was reworked by
548.An Henning Brauer Aq henning@openbsd.org .