dhcpd
dhcpd is the older Internet Systems Consortium (ISC) DHCP server. Be aware that dhcpd is no longer maintained as of January 2023; ISC promotes Kea as its official replacement.
Installation
Usage
dhcpd includes two unit files, dhcpd4.service
and dhcpd6.service
, which can be used to control the daemon. They start the daemon on all network interfaces for IPv4 and IPv6 respectively. See #Listening on only one interface for an alternative.
Configuration
Assign a static IPv4 address to the interface you want dhcpd to listen on (here eth0
). The specified subnet should not overlap with that of other interfaces.
# ip link set up dev eth0 # ip addr add 139.96.30.100/24 dev eth0 # arbitrary address
192.168/16
(subnet192.168.0.0
, netmask255.255.0.0
)172.16/12
(subnet172.16.0.0
, netmask255.240.0.0
)10/8
(for large networks; subnet10.0.0.0
, netmask255.0.0.0
)
The default configuration file dhcpd.conf
contains many uncommented examples, so relocate it:
# cp /etc/dhcpd.conf /etc/dhcpd.conf.example
To only listen on the subnet 139.96.30.0/24
, you may create the following minimal configuration file:
/etc/dhcpd.conf
option domain-name-servers 8.8.8.8, 8.8.4.4; option subnet-mask 255.255.255.0; option routers 139.96.30.100; subnet 139.96.30.0 netmask 255.255.255.0 { range 139.96.30.150 139.96.30.250; }
The options used in this configuration file are:
domain-name-servers
which contains addresses of DNS servers supplied to the clients. Here we use Google's public DNS servers. If you have configured your own DNS server on a local machine, specify its address in your subnet (here 139.96.30.0/24
).
subnet-mask
and routers
which define a subnet mask and a list of available routers on the subnet; routers
also defines the default gateway served to the client. For small networks, you can usually use 255.255.255.0
as a mask and specify an IP address of the machine on which you are running dhcpd (here 139.96.30.100
).
subnet
which defines options for separate subnets that are applied to the network interfaces on which dhcpd is listening. Here we have defined the range of available IP addresses for a single subnet 139.96.30.0/24
(on a single interface eth0
).
For a complete list of options, consult dhcpd.conf(5).
Listening on only one interface
If your computer is already part of one or several networks, it could be a problem if your computer starts giving ip addresses to machines from the other networks. It can be done by either configuring dhcpd or starting it as a daemon with systemctl.
Configuring dhcpd
In order to exclude an interface, you must create an empty declaration for the subnet that will be configured on that interface.
This is done by editing the configuration file (for example):
/etc/dhcpd.conf
# No DHCP service in DMZ network (192.168.2.0/24) subnet 192.168.2.0 netmask 255.255.255.0 { }
Service file
The default service file provided by dhcpd does not specify an interface. Use a drop-in unit file for the dhcpd4.service
as follows:
/etc/systemd/system/dhcpd4.service.d/override.conf
[Service] ExecStart= ExecStart=/usr/bin/dhcpd -4 -q -cf /etc/dhcpd.conf -pf /run/dhcpd4/dhcpd.pid %I
This allows using dhcpd4.service
as a template unit, binding dhcpd to a particular interface; for example dhcpd4@eth0.service
, where eth0 is the first enumerated Ethernet device.
Use for PXE
PXE Configuration is done with the following two options:
/etc/dhcpd.conf
next-server 192.168.0.2; filename "/pxelinux.0";
This section can either be in an entire subnet
or just in a host
definition. next-server
is the IP of the TFTP Server, and filename
is the filename of the image to boot. For more information see PXE.