The knowledge about the working and need of DHCP Servers is essential for a person to pass CCNA 100-101 ICND1 Exam as it is one of the major sections in the course outline.

What is DHCP Server?

DHCP stands for Dynamic Host Configuration Protocol. It is a Cisco device that can be used as a regular server for the purpose of issuing IP addresses using dynamic host configuration protocols.

Need for a DHCP Server:

DHCP Server is deployed to minimize the overall amount of configuration administrative burden on ourselves.servers1

Assigning IP addresses in medium sized Local Area Networks manually is a so much time consuming task. Assigning IP addresses manually can create a number of errors in configuration which can create problem in overall network and again require a time to
fix those errors. The manual work is also unfavorable for the employees because they need a lot of movement i.e. taking their laptops and other related devices from one place to another which can disturb the working environment.

The above discussed issues are the basic cause due to which DHCP servers are used to eliminate the above issue to a maximum level.

Deploying DHCP Server:
The IP address assignment through DHCP server in Local Area Network is centralized that enables consistency across the whole organization.

Understanding DHCP:


The communication between the End Host and a Server is four step process that can be memorized as DORA. Here D stands for Discover, O stands for Offer, R stands for Request and A stands for Acknowledgment.

  1. Discover:

In the discover step, the End Host send information via Broadcast to the DHCP server. In this phase the client requests for a DHCP address.

  1. Offer:

When the DHCP server receives the broadcast from a client, in return it sends an IP address to the client as an offer.

  1. Request:

In the third step the client accepts the offer by the server and say yes to the offered IP address.

  1. Acknowledgement:

It is the final step of whole scenario in which the server sends an acknowledgment to the client for the assignment of IP address.

So the above four step communication process allows the DHCP to see the request from a client and assign the dynamic IP address in return.

Configuring a DHCP Server:


We can configure DHCP server to run on different devices in a network like router and switches. DHCP server is configured to support LAN guest users.

Configuration Scenario:

  1. First of all the DHCP server is configured on a router in a network.
  2. The IP address assigned to a router is selected from the range of An IP address is assigned for almost 12 hours after which a new IP address is assigned so that it can be made dynamic. The IP address is rotated to strengthen the network or infrastructure.
  3. A range of IP addresses from to are not assigned to the devices during DHCP configuration. It should be kept in mind that the IP addresses should not be duplicated in a network because that will disturb the whole network.

Cisco IOS DHCP Configuration:
In this process, first of we have to exclude the range of IP address from to so that they should not be assigned to the devices.

  1. Branch (config) # ip dhcp pool Guests
  2. Branch (dhcp-config) # network
  3. Branch (dhcp-config) # default – router
  4. Branch (dhcp-config) # dns – server
  5. Branch (dhcp-config) # domain – name
  6. Branch (dhcp-config) # lease 0 12
  7. Branch (dhcp-config) # exit
  8. Branch (config) # ip dhcp excluded – address

In the first step we find a pool and give it a name as we named it as a ‘Guest’. In the second step we assign the networks to which we want to issue the address. In third step we issue the default router, it is the identity of the default gateway. In the next step we issue any DNS server that we have applied. In the fifth step we issue over domain name.  After that the time is allotted to the specific IP address for a device and it ranges from 0-12 hours. After the lease time is expired the IP address is refreshed.

DHCP Relay Agent:images
The DHCP Relay Agent is configured to centralize the DHCP servers operating at different location. The purpose of centralization is to manage different DHCP servers at different locations in less time and to prevent the replication of IP addresses assigned todifferent devices.

Working of DHCP Relay Agent:
The DHCP relay agent act as a middle agent between the client and DHCP server. All the communication between the server and client is done via that relay agent as shown in the figure below:


So from the above discussion we can conclude that the task of assigning dynamic IP addresses to the devices in a network can be automated through DHCP servers which lead to greater efficiency in terms of both time and cost. Moreover the DHCP servers deployed at different geographical location can be centralized by configuring DHCP Relay Agents which is helpful to minimize the rate of errors and all the servers can be operated from a single location.

Passing Cisco 100-101 Exam:
After getting all the technical knowledge about 100-101 exam, the candidate have to practice for better preparation of the real exam. The practice tests are a best tool / way to prepare for the real exam as it is a simulator of a real exam.

Finding these practice exams is not an issue now as Selftest Training, a leading name in the certifications industry, provides these practice tests to ensure that the candidate should pass the 100-101 exam in first attempt. Moreover, for the satisfaction of customer, a free demo of the product can be downloaded easily for the purpose of product quality evaluation. The practice test is available in two formats i.e. PDF practice tests and Practice test software. These products are delivered with 100% money back guarantee in case of failure.