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Diffstat (limited to 'sbin/dhclient/dhclient.8')
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diff --git a/sbin/dhclient/dhclient.8 b/sbin/dhclient/dhclient.8 new file mode 100644 index 0000000..a12952f --- /dev/null +++ b/sbin/dhclient/dhclient.8 @@ -0,0 +1,181 @@ +.\" $OpenBSD: dhclient.8,v 1.3 2004/04/09 18:30:15 jmc Exp $ +.\" +.\" Copyright (c) 1997 The Internet Software Consortium. +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. Neither the name of The Internet Software Consortium nor the names +.\" of its contributors may be used to endorse or promote products derived +.\" from this software without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND +.\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, +.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE +.\" DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR +.\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" This software has been written for the Internet Software Consortium +.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie +.\" Enterprises. To learn more about the Internet Software Consortium, +.\" see ``http://www.isc.org/isc''. To learn more about Vixie +.\" Enterprises, see ``http://www.vix.com''. +.Dd April 7, 2004 +.Dt DHCLIENT 8 +.Os +.Sh NAME +.Nm dhclient +.Nd Dynamic Host Configuration Protocol (DHCP) Client +.Sh SYNOPSIS +.Nm +.Op Fl dqu +.Op Fl c Ar file +.Op Fl l Ar file +.Ar interface +.Sh DESCRIPTION +The +.Nm +utility provides a means for configuring network interfaces using DHCP, BOOTP, +or if these protocols fail, by statically assigning an address. +.Pp +The name of the network interface that +.Nm +should attempt to +configure must be specified on the command line. +.Pp +The options are as follows: +.Bl -tag -width "-p port" +.It Fl c Ar file +Specify an alternate location, +.Ar file , +for the configuration file. +.It Fl d +Forces +.Nm +to always run as a foreground process. +By default, +.Nm +runs in the foreground until it has configured the interface, and then +will revert to running in the background. +.It Fl l Ar file +Specify an alternate location, +.Ar file , +for the leases file. +.It Fl q +Forces +.Nm +to be less verbose on startup. +.It Fl u +Forces +.Nm +to reject leases with unknown options in them. +The default behaviour is to accept such lease offers. +.El +.Pp +The DHCP protocol allows a host to contact a central server which +maintains a list of IP addresses which may be assigned on one or more +subnets. +A DHCP client may request an address from this pool, and +then use it on a temporary basis for communication on the network. +The DHCP protocol also provides a mechanism whereby a client can learn +important details about the network to which it is attached, such as +the location of a default router, the location of a name server, and +so on. +.Pp +On startup, +.Nm +reads +.Pa /etc/dhclient.conf +for configuration instructions. +It then gets a list of all the +network interfaces that are configured in the current system. +It then attempts to configure each interface with DHCP. +.Pp +In order to keep track of leases across system reboots and server +restarts, +.Nm +keeps a list of leases it has been assigned in the +.Pa /var/db/dhclient.leases.IFNAME +file. +.Qq IFNAME +represents the network interface of the DHCP client +.Pq e.g. em0 , +one for each interface. +On startup, after reading the +.Xr dhclient.conf 5 +file, +.Nm +reads the leases file to refresh its memory about what leases it has been +assigned. +.Pp +Old leases are kept around in case the DHCP server is unavailable when +.Nm +is first invoked (generally during the initial system boot +process). +In that event, old leases from the +.Pa dhclient.leases.IFNAME +file which have not yet expired are tested, and if they are determined to +be valid, they are used until either they expire or the DHCP server +becomes available. +.Pp +A mobile host which may sometimes need to access a network on which no +DHCP server exists may be preloaded with a lease for a fixed +address on that network. +When all attempts to contact a DHCP server have failed, +.Nm +will try to validate the static lease, and if it +succeeds, it will use that lease until it is restarted. +.Pp +A mobile host may also travel to some networks on which DHCP is not +available but BOOTP is. +In that case, it may be advantageous to +arrange with the network administrator for an entry on the BOOTP +database, so that the host can boot quickly on that network rather +than cycling through the list of old leases. +.Sh NOTES +You must have the Berkeley Packet Filter (BPF) configured in your kernel. +.Nm +requires at least one +.Pa /dev/bpf* +file for each broadcast network interface that is attached to your system. +See +.Xr bpf 4 +for more information. +.Sh FILES +.Bl -tag -width /var/db/dhclient.leases.IFNAME~ -compact +.It Pa /etc/dhclient.conf +DHCP client configuration file +.It Pa /var/db/dhclient.leases.IFNAME +database of acquired leases +.El +.Sh SEE ALSO +.Xr dhclient.conf 5 , +.Xr dhclient.leases 5 , +.Xr dhclient-script 8 , +.Xr dhcp 8 , +.Xr dhcpd 8 , +.Xr dhcrelay 8 +.Sh AUTHORS +.Nm +was written by +.An Ted Lemon Aq mellon@fugue.com +and +.An Elliot Poger Aq elliot@poger.com . +.Pp +The current implementation was reworked by +.An Henning Brauer Aq henning@openbsd.org . |