Dynamic Host Configuration Protocol

This guide shows how to use a Cisco router or layer 3 switch as a DHCP server, and serve IP addresses to client devices in a local area network.

Introduction

DHCP (Dynamic Host Configuration Protocol) is a network protocol used to automatically assign IP addresses and other network configuration settings to devices on a network. In a typical DHCP configuration, there are two main components: A DHCP server and DHCP clients. The DHCP server is responsible for assigning IP addresses and network configuration settings to clients, while the clients are responsible for requesting and receiving those settings from the DHCP server. DHCP allows network administrators to manage IP address allocation and network configuration centrally, which can simplify network administration and reduce the chance of conflicts between devices on the network. It also supports dynamic allocation of IP addresses, which means that IP addresses are only assigned to devices when they are needed, and can be released when they are no longer in use, which helps to conserve IP address space. The DHCP Process, also known as "DORA", is explained in the table below:

Description
The client sends a DHCPDISCOVER message to the network, requesting IP configuration settings.
Any available DHCP servers on the network will receive the DHCPDISCOVER message and respond with a DHCPOFFER message, which includes an IP address and other network configuration settings.
The client selects one of the DHCPOFFER messages and sends a DHCPREQUEST message to the server, requesting the offered configuration settings.
The DHCP server sends a DHCPACK message to the client, confirming the requested settings and providing a lease on the IP address.
Once the client has received the DHCPACK message, it can use the assigned IP address and other network configuration settings to communicate on the network.

Overview

A DHCP server is a network service that automatically assigns IP addresses and network configuration settings to devices on a network. A Cisco router or layer 3 switch can function as a DHCP server, allowing it to provide IP addresses and network configuration information to devices connected to the network. To configure a Cisco router as a DHCP server, the following steps are necessary:

Description
Gateway interfaces: The interfaces that will be used for DHCP must be configured with IP addresses and subnet masks.
DHCP pool: A DHCP pool is a range of IP addresses that the DHCP server will use to assign to clients. Define the DHCP pool using the "ip dhcp pool" command.
DHCP options: DHCP options are additional parameters that can be provided to clients, such as DNS server addresses and default gateway addresses.
Activate the DHCP server: To activate the DHCP server, it is necessary to enable the DHCP service on the device with the "service dhcp" command.

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