1 .\" $OpenBSD: dhclient.8,v 1.6 2007/05/31 19:19:43 jmc Exp $
2 .\" $DragonFly: src/sbin/dhclient/dhclient.8,v 1.3 2008/09/03 08:02:34 matthias Exp $
4 .\" Copyright (c) 1997 The Internet Software Consortium.
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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
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44 .Nd Dynamic Host Configuration Protocol (DHCP) Client
54 utility provides a means for configuring network interfaces using DHCP, BOOTP,
55 or if these protocols fail, by statically assigning an address.
57 The name of the network interface that
60 configure must be specified on the command line.
62 The options are as follows:
63 .Bl -tag -width "-p port"
65 Specify an alternate location,
67 for the configuration file.
71 to always run as a foreground process.
74 runs in the foreground until it has configured the interface, and then
75 will revert to running in the background.
77 Specify an alternate location,
83 to be less verbose on startup.
87 to reject leases with unknown options in them.
88 The default behaviour is to accept such lease offers.
91 The DHCP protocol allows a host to contact a central server which
92 maintains a list of IP addresses which may be assigned on one or more
94 A DHCP client may request an address from this pool, and
95 then use it on a temporary basis for communication on the network.
96 The DHCP protocol also provides a mechanism whereby a client can learn
97 important details about the network to which it is attached, such as
98 the location of a default router, the location of a name server, and
104 .Pa /etc/dhclient.conf
105 for configuration instructions.
106 It then gets a list of all the
107 network interfaces that are configured in the current system.
108 It then attempts to configure each interface with DHCP.
110 In order to keep track of leases across system reboots and server
113 keeps a list of leases it has been assigned in the
114 .Pa /var/db/dhclient.leases.IFNAME
117 represents the network interface of the DHCP client
119 one for each interface.
120 On startup, after reading the
124 reads the leases file to refresh its memory about what leases it has been
127 Old leases are kept around in case the DHCP server is unavailable when
129 is first invoked (generally during the initial system boot
131 In that event, old leases from the
132 .Pa dhclient.leases.IFNAME
133 file which have not yet expired are tested, and if they are determined to
134 be valid, they are used until either they expire or the DHCP server
137 A mobile host which may sometimes need to access a network on which no
138 DHCP server exists may be preloaded with a lease for a fixed
139 address on that network.
140 When all attempts to contact a DHCP server have failed,
142 will try to validate the static lease, and if it
143 succeeds, it will use that lease until it is restarted.
145 A mobile host may also travel to some networks on which DHCP is not
146 available but BOOTP is.
147 In that case, it may be advantageous to
148 arrange with the network administrator for an entry on the BOOTP
149 database, so that the host can boot quickly on that network rather
150 than cycling through the list of old leases.
152 You must have the Berkeley Packet Filter (BPF) configured in your kernel.
154 requires at least one
156 file for each broadcast network interface that is attached to your system.
159 for more information.
161 .Bl -tag -width /var/db/dhclient.leases.IFNAME~ -compact
162 .It Pa /etc/dhclient.conf
163 DHCP client configuration file
164 .It Pa /var/db/dhclient.leases.IFNAME
165 database of acquired leases
169 .Xr dhclient.conf 5 ,
170 .Xr dhclient.leases 5 ,
171 .Xr dhclient-script 8 ,
173 .Xr dhcpd 8 Pq Pa pkgsrc/net/isc-dhcpd4 ,
174 .Xr dhcrelay 8 Pq Pa pkgsrc/net/isc-dhcrelay4
179 .An Ted Lemon Aq mellon@fugue.com
181 .An Elliot Poger Aq elliot@poger.com .
183 The current implementation was reworked by
184 .An Henning Brauer Aq henning@openbsd.org
185 and was imported into