NetBSD DHCP HOWTO
DHCP Overview
DHCP Client Setup
DHCP Server Setup
DHCP Overview
Introduction and Purpose
This document attempts to explain how to setup DHCP clients and servers for the NetBSD operating system.
What is DHCP?
DHCP stands for Dynamic Host Configuration Protocol. It allows dynamic configuration of the network configuration of a host computer. The basic idea is this: When a DHCP client is turned on, it initially doesn't have an IP address assigned to it. It issues a broadcast message to any DHCP servers which are on the network. An exchange takes place during which the DHCP server assigns an IP address to the client and tells the client certain key network configuration parameters (such as name server addresses for example).
Who needs to use DHCP?
Many internet service providers (ISPs) require that their customers use a DHCP client so the ISP may dynamically assign IP addresses and control other network settings. Another use is for laptop computers which may be connected to more than one network. For example a laptop may be connected to a network in the office and also at home. This is an ideal use for DHCP as the laptop doesn't need to be manually reconfigured for use in the 2 different networks. In this case there needs to be a DHCP server both on the office network and the home network and the laptop needs a DHCP client.
Sources of More Detailed Information
For more information about DHCP in general, please refer to RFC 1541, Request for Comments document for the Dynamic Host Configuration Protocol (DHCP). In addition there is a comprehensive DHCP FAQ.
DHCP Client Setup
Configure DHCP
The DHCP client can be configured in the file
/etc/dhcpcd.conf
. If the file is not
present, DHCP will still work fine. See
dhcpcd.conf(5) and dhcpcd-run-hooks(8)
for more detailed information.
Enable DHCP
Edit /etc/rc.conf
and edit the
'dhcpcd
' line to read
'dhcpcd=YES
'. By default, DHCP requests
will be sent to all attached network interfaces. If you want
to only use DHCP on a single/less network cards, add a list
of network interfaces which should be configured with DHCP
to the 'dhcpcd_flags
' line. For example,
'dhcpcd_flags="wm0"
'.
The next time you reboot your machine it will configure
itself as a DHCP client. To enable DHCP without rebooting,
run the command 'service dhcpcd start
'.
How do I keep dhcpcd from nuking my /etc/resolv.conf?
Usually dhcpcd should rewrite your
/etc/resolv.conf
with information it
retrieved from the DHCP server. In the rare occasions that
this is not desired, you can add
dhcpcd_flags="-C resolv.conf"
to /etc/rc.conf
.
DHCP Server Setup
Introduction
This section shows how to setup a DHCP server. Note that you do not need to set up a DHCP server unless you want to dynamically assign addresses for computers on your LAN. For more detailed information see dhcpd(8), dhcpd.conf(5), and dhcp-options(5).
Configure DHCPD
The DHCP server configuration is contained in the file
/etc/dhcpd.conf
.
If this file does not exist on your system, you will have to
create it. Remember to customize this as needed, ie: change
the hostname stuff and the ethernet interface. A typical
/etc/dhcpd.conf
is shown below. In the
example, 7 addresses are made available for use by DHCP
clients. These addresses are 192.168.0.2 through
192.168.0.8. The DHCP server will tell the clients what IP
address, netmask, routers, name servers, and domain name to
use.
# Setting DHCPD global parameters allow unknown-clients; # Set parameters for the 192.168.0.0/24 subnet. subnet 192.168.0.0 netmask 255.255.255.0 { range 192.168.0.2 192.168.0.8; <=== Range of IP addresses available for assignment. default-lease-time 604800; <=== Default lease time in seconds. This is the time assigned if the client doesn't request one. max-lease-time 604800; <=== Maximum time a lease will be given. option subnet-mask 255.255.255.0; <=== subnetmask given to clients option domain-name-servers 1.2.3.4, 1.2.3.5; <=== put a list of name server IP addresses here. option domain-name "your.domain.name"; option routers 192.168.0.1; <=== list of routers the clients should use }
Enable DHCPD
Edit /etc/rc.conf
and edit the
'dhcpd
' line to read 'dhcpd=YES
'.
If you don't want to serve DHCP requests on all network
interfaces, add a list of network interfaces on which DHCPD
should run to the 'dhcpd_flags
' line. For
example, 'dhcpd_flags="-q ae1"
'.
Create a dhcpd.leases file
dhcpd wants a /var/db/dhcpd.leases
file to exist. Create it by running
'touch /var/db/dhcpd.leases
'.
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