Dynamic Host Configuration Protocol (DHCP) CCNA Exam Questions

Welcome to the Network Engineer Training tutorials by CoreNetworkZ Tech Solutions. Today, I will discuss about DHCP.

So, what is DHCP?

Dynamic Host Configuration Protocol (DHCP) is an application layer protocol that automatically assigns IP addresses to devices on a network.

Anagha Sivakumar, a Network Engineer trainee at CoreNetworkZ Tech Solutions, asked, "What is the role of DHCP in networking?"

I know many of my students might have the same question. Let me explain it. DHCP simplifies the process of assigning IP addresses to connected devices.

Imagine managing a network with thousands of devices. Do you think it is practical to assign static IP addresses to each one manually, without errors? That is where DHCP comes in.

It allows devices to obtain IP addresses automatically, reducing human error and administrative burden.

Nimin Marcos, a regular reader of CoreNetworkZ Tech Solutions, mentioned a question in our support forum. He asked, "Hello Alex, can you explain the complete working of Dynamic Host Configuration Protocol?"

DHCP operates on a client-server model, where the server assigns IP addresses and other network configuration details to client devices. Let us explore how DHCP functions within a network.

We can use the term DORA to explain the working of DHCP. It is a four-stage process.

Let us check each stage.

1. D-- Discovery

   When a client connects to a network, it sends a broadcast to discover the DHCP server. This broadcast is termed DHCPDISCOVER.

   
   

2. O--- Offer

   At this stage, the server responds to the client DISCOVERY message and sends a DHCPOFFER unicast message. DHCPOFFER includes IP address, subnet mask, default gateway address, DNS address, etc.

   
   

3. R---- Request

   Here the client sends a DHCPREQUEST message to the server.

   
   

4. A--- Acknowledgment

   Here server sends an acknowledgment (DHCPACK) to the client indicating it received the DHCPREQUEST from the client, and the client accepted the IP address information.

Ashi Vohra, a client of CoreNetworkZ Tech Solutions, asked, "What are the advantages of using the dynamic host configuration protocol (dhcp)?"

I developed three network apps for his company. One of them used the DHCP feature. So, he asked this question.

The advantages of using Dynamic Host Configuration Protocol are:

1. There is no chance of getting IP addressing errors if you use DHCP to assign IP addresses to devices in a network.

2. The second advantage of using Dynamic Host Configuration Protocol in a network is the efficient control of IP addressing. The reason is simple. It is centralized.

3. The third advantage is scalability and cost-effectiveness.

Allen Donald asked in a comment why I said cost-effectiveness as an advantage. It is simple. We can avoid the heavy work of manual IP addressing once DHCP assigns IP addresses automatically.

If you prepare for Cisco certification exams( like CCNA), you must learn more about DHCP. If you follow the CCNA DUMP for your next exam, let me help you in this section.

A few students asked for my support in learning CCNA questions from the DHCP section. Some important points about Dynamic Host Configuration Protocol for your Cisco Certification exams are listed below.

• Command to Enable or Disable DHCP on Cisco IOS Router --service dhcp
  
  
• Cisco Command to create address pool -- ip dhcp pool
  
  
• Command to assign a domain name to client --domain-name
  
  
• Command to specify DHCP IP range -- network
  
  
• The command to check if the server can use an IP address in the pool -ip dhcp ping timeout
  
  
• The command to exclude an IP address from the DHCP address pool --ip dhcp excluded-address
  
  
• Show addresses assigned to clients --show ip dhcp binding
  
  
• DHCPNACK - This acknowledgment from the server tells the client the offer is no longer valid.
  
  
• DHCPDECLINE - The client tells the server, it cannot use the offer from the server.

Let me share a few more expected CCNA questions from DHCP.

Sanal Mohan, a student preparing for CCNA, asked, "Does DHCP use ports to communicate? If yes, which ports it uses?"

DHCP servers use UDP port 67 to receive requests, while clients use UDP port 68 to send them.

Ashams asked in our support forum, "What is the default lease time of an IP address assigned by DHCP?" DHCP assigns IP addresses by default with a lease time of 24 hours. However, network administrators can change it.

Ashish Mudgal, a senior Network Engineer at CoreNetworkZ Tech Solutions, mentioned, "One critical point many students do not know is DHCP communicates using the UDP protocol. "

1. https://www.juniper.net/documentation/us/en/software/junos/dhcp/index.html
2. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-sy/dhcp-15-sy-book/config-dhcp-server.html
3. https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/networking_guide/sec-dhcp-configuring-server
4. https://learn.microsoft.com/en-us/windows-server/networking/technologies/dhcp/dhcp-top