Data Networking/Fall 2014/Priya/DHCP/configure

In this article, we will describe the steps and procedures required to install and configure ISC-DHCP server on a Linux machine, (specifically Ubuntu 14.04).

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.

    sudo apt-get update     

Installs ISC-DHCP Server

    sudo apt-get install isc-dhcp-server

Step 2
Configuring ISC-DHCP sever - dhcpd.conf

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

    sudo nano /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 192.168.3.0 netmask 255.255.255.0 {
        range 192.168.3.10 192.168.3.45;
        range 192.168.3.55 192.168.3.120;
        option routers 192.168.3.1;
        option broadcast-address 192.168.3.255;
        default-lease-time 3600;
        max-lease-time 7200;
    }
        option domain-name-servers 192.168.3.51 192.168.3.54;
        option domain-name "neunetworks.com";

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

     authoritative;

Reservation Fixed IP addresses can be assigned to particular clients. Here I have assigned fixed IP addresses to DNS Server, Web server and a host in the network.

     host webserver1 {
        hardware ethernet bc:77:37:b1:19:0d;
        fixed-address 192.168.3.50;
     }
     host dnsserver1 {
        hardware ethernet 30:10:b3:14:6e:57;
        fixed-address 192.168.3.51;
     }
     host client1 {
        hardware ethernet 80:86:f2:d5:0e:ad; 
        fixed-address 192.168.3.100;
     }

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.

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

We have to set the interfaces to wlan0 in our file

     INTERFACES= "wlan0"

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

     ip route

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

    sudo service isc-dhcp-server restart
    sudo service isc-dhcp-server start
    sudo service isc-dhcp-server stop

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

     cd /var/lib/dhcp/
     ls -l
     cat dhcpd.leases