Install DHCP on Ubuntu 22.04
From: https://ubuntu.com/server/docs/network-dhcp
Dynamic Host Configuration Protocol (DHCP)
The Dynamic Host Configuration Protocol (DHCP) is a network service that
enables host computers to be automatically assigned settings from a server
as opposed to manually configuring each network host. Computers configured
to be DHCP clients have no control over the settings they receive from the
DHCP server, and the configuration is transparent to the computer’s user.
The most common settings provided by a DHCP server to DHCP clients include:
- IP address and netmask
- IP address of the default-gateway to use
- IP addresses of the DNS servers to use
However, a DHCP server can also supply configuration properties such as:
- Hostname
- Domain name
- Time server
- Print server
The advantage of using DHCP is that any changes to the network, such as a
change in the DNS server address, only need to be changed at the DHCP
server, and all network hosts will be reconfigured the next time their DHCP
clients poll the DHCP server. As an added advantage, it is also easier to
integrate new computers into the network, as there is no need to check for
the availability of an IP address. Conflicts in IP address allocation are
also reduced.
A DHCP server can provide configuration settings using the following methods:
- Manual allocation (MAC address)
This method uses DHCP to identify the unique hardware address of each
network card connected to the network, and then supplies a constant
configuration each time the DHCP client makes a request to the DHCP server
using that network device. This ensures that a particular address is
assigned automatically to that network card, based on its MAC address.
- Dynamic allocation (address pool)
In this method, the DHCP server assigns an IP address from a pool of
addresses (sometimes also called a range or scope) for a period of time (or
lease) configured on the server, or until the client informs the server that
it doesn’t need the address anymore. This way, the clients receive their
configuration properties dynamically and on a “first come, first served”
basis. When a DHCP client is no longer on the network for a specified
period, the configuration is expired and released back to the address pool
for use by other DHCP clients. This way, an address can be leased or used
for a period of time. After this period, the client must renegotiate the
lease with the server to maintain use of the address.
- Automatic allocation
Using this method, the DHCP automatically assigns an IP address
permanently to a device, selecting it from a pool of available addresses.
Usually, DHCP is used to assign a temporary address to a client, but a DHCP
server can allow an infinite lease time.
The last two methods can be considered “automatic” because in each case
the DHCP server assigns an address with no extra intervention needed. The
only difference between them is in how long the IP address is leased; in
other words, whether a client’s address varies over time. The DHCP server
that Ubuntu makes available is dhcpd (dynamic host configuration protocol
daemon), which is easy to install and configure and will be automatically
started at system boot.
Install dhcpd
At a terminal prompt, enter the following command to install dhcpd:
apt install isc-dhcp-server
Note:
dhcpd’s messages are being sent to syslog. Look there for diagnostics messages.
Configure dhcpd
You will probably need to change the default configuration by editing
/etc/dhcp/dhcpd.conf to suit your needs and particular configuration.
Most commonly, what you want to do is assign an IP address randomly. This
can be done with settings as follows:
# minimal sample /etc/dhcp/dhcpd.conf
default-lease-time 600;
max-lease-time 7200;
subnet 192.168.1.0 netmask 255.255.255.0
{
range 192.168.1.150 192.168.1.200;
option routers 192.168.1.254;
option domain-name-servers 192.168.1.1, 192.168.1.2;
option domain-name "mydomain.example";
}
This will result in the DHCP server giving clients an IP address from the
range 192.168.1.150–192.168.1.200. It will lease an IP address for 600
seconds if the client doesn’t ask for a specific time frame. Otherwise the
maximum (allowed) lease will be 7200 seconds. The server will also
“advise” the client to use 192.168.1.254 as the default-gateway and
192.168.1.1 and 192.168.1.2 as its DNS servers.
You also may need to edit /etc/default/isc-dhcp-server to specify the
interfaces dhcpd should listen to.
INTERFACESv4="eth4"
After changing the config files you need to restart the dhcpd service:
systemctl restart isc-dhcp-server.service
References