Step 1
Installing isc-dhcp server

To install isc-dhcp server on Ubuntu 14.04, use the following commands Update Linux files

Update command will fetch the packages from its location and updates them to newer version.

# apt update

Installs isc-dhcp Server

# apt install isc-dhcp-server

Step 2

Configuring isc-dhcp sever – /etc/dhcp/dhcpd.conf

The isc-dhcp server configuration file is dhcpd.conf and can be accessed using the following command

# vi /etc/dhcp/dhcpd.conf

This command will allow to make changes in the dhcp configuration file “dhcpd.conf” which is at specified path.

We are required to do the following modifications in dhcpd.conf file:

subnet netmask {
    option routers;
    option broadcast-address;
    default-lease-time 3600;
    max-lease-time 7200;
option domain-name-servers;
option domain-name "";  // specified my domain

The following command is used to make the DHCP server an authoritative server for local network.


The following command is used to check the syntax of dhcpd.conf file for errors

# dhcpd -t

The following command will allow to edit the isc-dhcp-server file, where we can manually determine the interface of the server.

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

We have to set the interfaces to wlan0 in our file

     INTERFACES= "en0"

The following line will display the contents of the current routing tables.

# ip route list
Setting for diskless system
 # A slightly different configuration for an internal subnet.
subnet netmask {

  allow booting;
  allow bootp;

 group {
    option domain-name-servers;
    option domain-name "";
    filename "pxelinux.0";
    include "/etc/dhcp/fixed_ip.conf";

  option domain-name-servers,,;
  option domain-name "";
  option routers;
  option broadcast-address;
  default-lease-time 600;
  max-lease-time 7200;
# End of subnet

‘next-server’ IP is written for ‘diskless NFS server’ IP.
‘filename’  include pxelinux package. it’s put into tftpsever root.
Example fixed_ip.conf

# dhcp for fixed ip
# included by /etc/dhcp/dhcpd.conf
# following for pxe boot
host host-name {
  hardware ethernet 00:aa:aa:aa:aa:aa;
  option host-name "host-name";

Step 3
Securing DHCP server The following modifications are done to configuration file to secure the DHCP server

ddns-update-style none;
deny declines;
deny bootp;

The DoS attack on DHCP server can be avoided by denying the DHCP decline messages and can deny supporting old bootp clients.

Step 4
Restart isc-dhcp server

Now that the isc-dhcp-server configuration is complete, we need to reload the dhcp server, so that the new configurations can be implemented

# systemctl isc-dhcp-server restart
# systemctl isc-dhcp-server start
# systemctl isc-dhcp-server stop

Step 5
Verifying.. Inorder to check the leases of the IP addresses assigned by the DHCP

# less /var/lib/dhcp/dhcpd.leases