.\"     $OpenBSD: dhcp.8,v 1.23 2007/05/31 19:19:59 jmc Exp $
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.\" Copyright (c) 1999 Aaron Campbell
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.Dd $Mdocdate: May 31 2007 $
.Dt DHCP 8
.Os
.Sh NAME
.Nm dhcp
.Nd configuring
.Ox
for DHCP
.Sh DESCRIPTION
The Dynamic Host Configuration Protocol (DHCP) allows hosts on a TCP/IP network
to configure one or more network interfaces based on information collected from
a DHCP server in response to a DHCP request.
This mechanism is often used, for example, by cable modem and DSL network
providers to simplify network configurations for their clients/customers.
.Pp
Information typically contained within a DHCP response includes an IP
address for the interface, subnet mask, broadcast address, router (gateway)
listing, domain name server listing, and the interface's MTU.
.Pp
To set up
.Ox
as a DHCP client:
.Bl -enum -offset indent
.It
For each interface that is to be configured via DHCP, create a
.Pa /etc/hostname.XXX
file (where XXX is the interface's identifier, e.g., ep1) that starts with
the word
.Dq dhcp ,
optionally followed by additional interface options.
See
.Xr hostname.if 5
for more information on the format of these files.
.Pp
The
.Pa /etc/netstart
script reads each of these hostname files at boot-time and runs the
.Xr dhclient 8
program for each interface that is to be configured via DHCP.
.It
[Optional] To tweak settings, edit
.Pa /etc/dhclient.conf .
This file is shipped with the system.
See
.Xr dhclient.conf 5
and
.Xr dhclient 8
for details.
.El
.Pp
To set up
.Ox
as a DHCP server:
.Bl -enum -offset indent
.It
Edit
.Pa /etc/dhcpd.conf .
This file is shipped with the system.
See
.Xr dhcpd.conf 5
and
.Xr dhcpd 8
for details.
.It
Edit
.Pa /etc/dhcpd.interfaces .
This file should contain a list of interfaces you wish to serve by
.Xr dhcpd 8 .
If you have only one broadcast network interface or you wish to serve all
interfaces, this step is not required.
Be sure to leave this file empty (or even delete it) if this is the case.
.It
Edit
.Pa /etc/rc.conf.local
and set
.Cm dhcpd_flags="" .
This will cause
.Ox
to start the
.Xr dhcpd 8
daemon at boot-time and listen for DHCP requests on the local network.
To start it manually, execute the following command:
.Pp
.Dl # /usr/sbin/dhcpd [netif1 netif2 ...]
.El
.Pp
The DHCP client and server use the Berkeley Packet Filter (BPF).
Ensure the kernel has been compiled with BPF support
and at least one
.Pa /dev/bpf*
file exists per broadcast network interface that is attached to the system.
This is almost always the case and should only be considered if all other
troubleshooting options have failed.
.Pp
See
.Xr dhcpd 8
for information on other available options.
Note, however, that most of the flags are useful only for debugging purposes.
.Sh FILES
.Bl -tag -width /etc/dhcpd.interfaces -compact
.It Pa /etc/dhcpd.conf
DHCP server configuration file
.It Pa /etc/dhcpd.interfaces
list of network interfaces served by
.Xr dhcpd 8
.It Pa /etc/rc.conf.local
configuration file where
.Cm dhcpd_flags
must be set
.It Pa /etc/dhclient.conf
DHCP client configuration file
.It Pa /etc/hostname.XXX
interface-specific configuration files
.El
.Sh SEE ALSO
.Xr dhclient.conf 5 ,
.Xr dhcpd.conf 5 ,
.Xr hostname.if 5 ,
.Xr dhclient 8 ,
.Xr dhcpd 8 ,
.Xr dhcrelay 8