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DHCP (Dynamic Host Configuration Protocol)

Category: DHCP
Author: gokhankosem, on 09 Oct 17 - 0 Comments
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DHCP (Dynamic Host Configuration

Protocol)



DHCP (Dynamic Host Configuration Protocol) Overview

In a network all the Layer 3 devices need to have an IP address. These IP addresses can be given manually one by one or dynamically and automaticallywith IP address allocation mechanim, DHCP (Dynamic Host Configuration Protocol). Here, beside IP addresses, other IP related allocation is also done with DHCP.

DHCP has three IP Allocation Mechanisms. These are:

• Dynamic
• Automatic
• Manual

In Dynamic IP Allocation, IP address is assigned from a predefined Pool and can be cancelled.

In Automatic IP Allocation, again, IP address is assigned from a predefined Pool, but this time can not be cancelled.

In Manuel IP Allocation, the allocation is done according to request of host and this is a range out of the pool.

If, DHCP assigns IP addresses from its predefined IP Pools dynamically, it leases these IP addresses for a short time to the DHCP Client. And DHCP Client uses this IP address until it expires. Before the expiration, DHCP Client request renewal or another IP address.

In DHCP terminology, there are different devices and roles. These devices and roles are:

• DHCP Server
• DHCP Client
• DHCP Relay Agent

DHCP Server is the device on which the DHCP configurations are done. All the configurations like IP Address Pools, Gateway Address etc. are done on DHCP Server. It is the mechanims that has the IP pools and provides IP addresses to the other nodes.


dhcp-server-client

DHCP Client is the other hosts here. The devices that need IP in a network is the DHCP Client for DHCP Server. To be so, it is also need to be configured to use this DHCP Server.

DHCP Relay Agent is the device stays between the DHCP Client and DHCP Server if these two main DHCP elements are in different networks. Some of the messages of the DHCP are broadcast. So, normally, Broadcast do not pass from one network to an another network. Here, Relay agents converts these broadcast messages to unicast messages.

dhcp-relay-agent-messages

DHCP Messages

DHCP Address Allocation is done via DHCP messages. With these messages, DHCP Server that will assign IP address, is determined, IP address assignments is done and other IP allocation actions achieved.

What are these DHCP Messages? These DHCP messages are:

• DHCP Discover
• DHCP Offer
• DHCP Request
• DHCP Ack
• DHCP Nak
• DHCP Release
• DHCP Decline
• DHCP Inform

The first four of these messages are used a successfull DHCP IP Allocation Operation.

dhcp-ip-allocation-messages

We will talk about DHCP Messages deeply, in the DHCP IP Allocation Operation article.

Below, you can see the picture of this details ;)

dhcp-messages-and-functions

Are There Any Other IP Allocation Protocol?

IP allocation is an important process for networks. And this is done via DHCP very efficiently.

There is also another protocol for IP allocation that is very old. This Protocol is BOOTP. The long name of it is BOOTstrap Protocol. Previously, it was used to assign IP addresses to the devices during boot process. But, nowadays, it is rarely used.

Other DHCP Articles:

DHCP Overview
DHCP IP Allocation Operation
Cisco DHCP Configuration With Packet Tracer
Huawei DHCP Configuration

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About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

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