Ubuntu 16.04 : Install & Monitor DHCP Server in Ubuntu 16.04

Install DHCP Server in Ubuntu 16.04

For the purpose of this tutorial, I will be using the following system as DHCP server.
My DHCP Server:

• OS – Ubuntu 16.04 LTS 64 bit
• IP Address – 192.168.1.105/24
• Hostname – ubuntuserver.ostechnix.lan

Open Terminal and run the following command to install DHCP server:

sudo apt-get install isc-dhcp-server

DHCP server has been installed. Now, let us go further and configure it to suit our needs.

Configure DHCP server

The default configuration file of DHCP server is /etc/default/isc-dhcp-server. We need to edit and modify it as per our requirements.

If you have more than one Network interface card in your DHCP server, you need to mention on which interface should the DHCP server serve DHCP requests.

As I have only one NIC in my server, I assigned ‘enp0s3’ as the listening interface. Here, enp0s3 is network card’s name.

To do so, edit /etc/default/isc-dhcp-server configuration file:

sudo vi /etc/default/isc-dhcp-server

Assign the network interface:

[...] INTERFACES="enp0s3"

If you have more than one interfaces, mention them with spaces, for example “eth0 eth1”.

Save and close the file.

Then, edit dhcpd.conf file,

sudo vi /etc/dhcp/dhcpd.conf

Modify it as shown below. Replace the domain name with your own values.

Enter the domain name and domain-name-servers:

[...] # option definitions common to all supported networks... option domain-name "ostechnix.lan"; option domain-name-servers ubuntuserver.ostechnix.lan; [...]

To make this server as official DHCP for your clients, find and uncomment the following line:

[...] authoritative; [...]

Scroll down little bit, and define the subnet, IP range, domain and domain name servers like below.

[...] # A slightly different configuration for an internal subnet. subnet 192.168.1.0 netmask 255.255.255.0 { range 192.168.1.20 192.168.1.30; option domain-name-servers ubuntuserver.ostechnix.lan; option domain-name "ostechnix.lan"; option routers 192.168.1.1; option broadcast-address 192.168.1.255; default-lease-time 600; max-lease-time 7200; } [...]

As you see in the above configuration, I have assigned IP range from 192.168.1.150 to 192.168.1.200. So, the DHCP clients will get the IP address from this range. But, what if you want assign a specific IP (fixed IP address) to a particular client? It’s easy too. You can easily assign a specific IP to a client of your network by adding the MAC id of that client with fixed IP address as shown below.

For example, let us say we want to assign IP 192.168.1.160 to client that has MAC id 00:22:64:4f:e9:3a. To find out the IP ann MAC addresses, use ‘ifconfig’ command.

ifconfig

Sample output:

See the underlined words. Those are the IP and MAC addresses.

Assign the fixed IP and MAC id of the client as shown below.

[...] host ubuntu-client { hardware ethernet 08:00:27:13:14:d5; fixed-address 192.168.1.160; } [...]

Once you modified all settings as per your requirements, save and close the file.

Now, restart dhcp service:

sudo systemctl restart isc-dhcp-server

Make sure you haven’t left any unused entries in the dhcpd.conf file. If there is any unused or unnecessary lines, just comment them out. Otherwise, DHCP service will not start.

Let us check if our DHCP service has been started or not using command:

sudo systemctl status isc-dhcp-server

Sample output:

As you see in the above screenshot, DHCP server is running!

To start or stop DHCP service, use the following commands:

sudo systemctl start isc-dhcp-serversudo systemctl stop isc-dhcp-server

At this stage, you will have a working DHCP server. The server side configuration part is over. Let’s go ahead and configure the DHCP clients.

Configure DHCP Clients

For the purpose of this tutorial, I will be using Ubuntu 16.04 LTS desktop as my DHCP client.

My DHCP client:

• OS – Ubuntu 16.04 LTS desktop
• IP Address – DHCP enabled

Open Network Connections either from Unity dash or Menu.

In the Network connections window, Select your Ethernet card and click Edit.

Click IPv4 Settings, and select “Automatic (DHCP)” option. Finally click Save.

Now, restart your client system, and check the IP address of your client system.

ifconfig

Sample output:

You will see a new IP address from IP range, which we defined in the DHCP server, is assigned to your client system.

As you see in the above screenshot, My Ubuntu 16.04 LTS desktop system, which has MAC id 08:00:27:13:14:d5, has been assigned with a fixed IP address (192.168.1.160) from the DHCP server. Remember we have mentioned these values in dhcpd.conf file of our DHCP server.

Congratulations! DHCP server is working!!

How to monitor DHCP server usage

Monitor DHCP server usage

I have tested this script in Ubuntu 16.04 LTS server. It worked just fine. Please note that the location of dhcpd.leases file might be different in some Linux distributions. You need to mention correct file name in the server. In Ubuntu 16.04 LTS server, you can find correct location of dhcpd.leases file under /var/lib/dhcp/ location. The author have mentioned /var/lib/dhcpd/dhcpd.leases in this script. It doesn’t work for me. I replaced the path with correct location i.e /var/lib/dhcp/dhcpd.leases in Ubuntu 16.04 systems.

Here I have included the complete script. Just coy and paste it to a text file and save it with .sh extension. For the purpose of this tutorial, I have it as monitor_dhcp.sh.

 Download the script from the following location.

• Monitoring DHCP usage script

Once downloaded, make it as executable using as shown below.

sudo chmod +x monitor_dhcp.sh

Now, run the following command to monitor DHCP server’s usage.

./monitor_dhcp.sh

Sample output:

--------- Total Count- Active & Non Active ----------- Total Active User : 2 Total Non Active User : 1 ------------------------------------------------------

As you see in the above output, there are two active users, and one non-active user.

Alternatively, you can check the DHCP client details using the log file.

cat /tmp/showdhcp.log

Sample output:

IP Addr Status MAC Host Name 192.168.1.150 free xx:xx:xx:xx:xx:xx 192.168.1.151 active xx:xx:xx:xx:xx:xx "sk" 192.168.1.152 free xx:xx:xx:xx:xx:xx