1 .\" $OpenBSD: dhclient.8,v 1.3 2004/04/09 18:30:15 jmc Exp $
3 .\" Copyright (c) 1997 The Internet Software Consortium.
4 .\" All rights reserved.
6 .\" Redistribution and use in source and binary forms, with or without
7 .\" modification, are permitted provided that the following conditions
10 .\" 1. Redistributions of source code must retain the above copyright
11 .\" notice, this list of conditions and the following disclaimer.
12 .\" 2. Redistributions in binary form must reproduce the above copyright
13 .\" notice, this list of conditions and the following disclaimer in the
14 .\" documentation and/or other materials provided with the distribution.
15 .\" 3. Neither the name of The Internet Software Consortium nor the names
16 .\" of its contributors may be used to endorse or promote products derived
17 .\" from this software without specific prior written permission.
19 .\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
20 .\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
21 .\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
22 .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
23 .\" DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
24 .\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
25 .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
26 .\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
27 .\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
28 .\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30 .\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 .\" This software has been written for the Internet Software Consortium
34 .\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
35 .\" Enterprises. To learn more about the Internet Software Consortium,
36 .\" see ``http://www.isc.org/isc''. To learn more about Vixie
37 .\" Enterprises, see ``http://www.vix.com''.
43 .Nd Dynamic Host Configuration Protocol (DHCP) Client
53 utility provides a means for configuring network interfaces using DHCP, BOOTP,
54 or if these protocols fail, by statically assigning an address.
56 The name of the network interface that
59 configure must be specified on the command line.
61 The options are as follows:
62 .Bl -tag -width "-p port"
64 Specify an alternate location,
66 for the configuration file.
70 to always run as a foreground process.
73 runs in the foreground until it has configured the interface, and then
74 will revert to running in the background.
76 Specify an alternate location,
82 to be less verbose on startup.
86 to reject leases with unknown options in them.
87 The default behaviour is to accept such lease offers.
90 The DHCP protocol allows a host to contact a central server which
91 maintains a list of IP addresses which may be assigned on one or more
93 A DHCP client may request an address from this pool, and
94 then use it on a temporary basis for communication on the network.
95 The DHCP protocol also provides a mechanism whereby a client can learn
96 important details about the network to which it is attached, such as
97 the location of a default router, the location of a name server, and
103 .Pa /etc/dhclient.conf
104 for configuration instructions.
105 It then gets a list of all the
106 network interfaces that are configured in the current system.
107 It then attempts to configure each interface with DHCP.
109 In order to keep track of leases across system reboots and server
112 keeps a list of leases it has been assigned in the
113 .Pa /var/db/dhclient.leases.IFNAME
116 represents the network interface of the DHCP client
118 one for each interface.
119 On startup, after reading the
123 reads the leases file to refresh its memory about what leases it has been
126 Old leases are kept around in case the DHCP server is unavailable when
128 is first invoked (generally during the initial system boot
130 In that event, old leases from the
131 .Pa dhclient.leases.IFNAME
132 file which have not yet expired are tested, and if they are determined to
133 be valid, they are used until either they expire or the DHCP server
136 A mobile host which may sometimes need to access a network on which no
137 DHCP server exists may be preloaded with a lease for a fixed
138 address on that network.
139 When all attempts to contact a DHCP server have failed,
141 will try to validate the static lease, and if it
142 succeeds, it will use that lease until it is restarted.
144 A mobile host may also travel to some networks on which DHCP is not
145 available but BOOTP is.
146 In that case, it may be advantageous to
147 arrange with the network administrator for an entry on the BOOTP
148 database, so that the host can boot quickly on that network rather
149 than cycling through the list of old leases.
151 You must have the Berkeley Packet Filter (BPF) configured in your kernel.
153 requires at least one
155 file for each broadcast network interface that is attached to your system.
158 for more information.
160 .Bl -tag -width /var/db/dhclient.leases.IFNAME~ -compact
161 .It Pa /etc/dhclient.conf
162 DHCP client configuration file
163 .It Pa /var/db/dhclient.leases.IFNAME
164 database of acquired leases
167 .Xr dhclient.conf 5 ,
168 .Xr dhclient.leases 5 ,
169 .Xr dhclient-script 8 ,
176 .An Ted Lemon Aq mellon@fugue.com
178 .An Elliot Poger Aq elliot@poger.com .
180 The current implementation was reworked by
181 .An Henning Brauer Aq henning@openbsd.org .