DHCP Configuration

Dynamic Host Configuration Protocol is a network protocol used to dynamically distribute network configuration parameters, such as IP addresses, gateway, and DNS for network interfaces. DHCP Server assigns IP addresses automatically to all systems, so system admin need not assign IP addresses manually to client machines in the network.

In this tutorial, we will cover how to install and configure a DHCP server in CentOS 7/RHEL 7

Testing Environment Setup

DHCP Server – Centos7.4

DCHP Client – Centos7.4, Red Hat 7.4 , Ubuntu 16.04, Windows- 8 & 10

DHCP Port                                                                       

dhcp server port – UDP port no -67

dhcp client port – UDP-port no- 68

Note: The server listens on port 67 for requests and

responses to the client on port 68.

DHCP works on DORA Concept

D : DISCOVER  

O : OFFER

R : REQUEST

A : ACKNOWLEDGMENT

Let's briefly explain How to DHCP Work ?

1. When a client computer (configured to use DHCP) and connected to a network is powered on, it forwards a DHCPDISCOVER broadcast (IP 255.255.255.255) message to the DHCP server.  If there is one or more DHCP servers on the network , they will hear the request on port 67.

2. After the DHCP server receives the DHCPDISCOVER request message, it replies with a IP lease  DHCPOFFER message. The reply use the broadcast address 255.255.255.255 but the frame contains the MAC address of the sending Client , so only the requesting device receives the offer.

3. Now the client receives the DHCPOFFER message, and it sends a DHCPREQUEST message to the server indicating, it is prepared to get the network configuration offered in the DHCPOFFER message.

4. After that DHCP server receives the DHCPREQUEST message from the client, and sends the DHCPACK message showing that the client is now permitted to use the IP address assigned to it.

Installing DHCP Server

Using below given command, we install DHCP Server on Centos7.4

Important: Assume that there are more than one network interface connected to the system, but you want the DHCP server to be started only on one of the interfaces, set the DHCP server to start only on that interface.

Open the file / etc / sysconfig / dhcpd, add the name of the specific interface to the list of DHCPDARGS, for example if the interface is em1, add:

Now Save the file and exit.

Configuring DHCP Server

The sample of DHCP configuration file is given in path :  /usr/share/doc/dhcp*/dhcpd.conf.sample

Now see the sample DHCP configuration file and set your configuration according to your requirement.

 Add the option given below:

# Common configurations to all supported networks...

   authoritative;

   ddns-update-style interim;

   ignore client-updates;

   option tftp-server-name "ck.cdot.in";

   subnet 10.5.5.0  netmask 255.255.255.0{

   range 10.5.5.2  10.5.5.150;

   range 10.5.5.160  10.5.5.254;

   option routers 10.5.5.1;

   option ip-forwarding off;

   option broadcast-address 10.5.5.255;

   default-lease-time 4600;

   max-lease-time 7200;

   option domain-name-servers 196.1.109.47;

   option domain-name "cdotd.in;

# Assign static IP to DHCP client….

  host Centos {

  hardware  ethernet 0:0:c0:5d:bd:98;

  fixed-address 10.5.5.151;

  host Red Hat {

  hardware  ethernet 0:0:c0:5d:bd:95;

  fixed-address 10.5.5.152;

  }

  host Ubuntu {

  hardware  ethernet 08:00:07:26:c0:a5;

  fixed-address 10.5.5.153;

  }

  host Windows {

  hardware  ethernet 00:4j:8k:13:8g:3a;

  fixed-address 10.5.5.154;

  }

Now save the file and close it

Note: you can find out the Linux MAC address using command.

Now start the DHCP service for the mean time and enable it to start automatically from the next system boot using the following commands:

Client – Centos7.4

Add the option given below:

   TYPE=Ethernet

   PROXY_METHOD=none

   BROWSER_ONLY=no

   BOOTPROTO=dhcp

   DEFROUTE=yes

   IPV4_FAILURE_FATAL=no

   NAME="Profile 1"

   UUID=e48ef4ab-e915-4061-a251-b796ce4fe8d1

   ONBOOT=yes

Now save the file and close it

Restart the network service