Free CCNA | DNS | Day 38 | CCNA 200-301 Complete Course

Introduction

In this tutorial, you will learn about the Domain Name System (DNS) as covered in Day 38 of Jeremy's IT Lab's CCNA 200-301 course. DNS is crucial for translating human-readable domain names into IP addresses, enabling easier navigation of the internet. This guide will walk you through the essential concepts and practical applications of DNS, including commands, configuration, and demonstrations.

Step 1: Understand the Purpose of DNS

• DNS serves as the phonebook of the internet, converting domain names (like www.example.com) into IP addresses that computers can understand.
• This system allows users to access websites using easy-to-remember names instead of complex numerical addresses.

Step 2: Use 'ipconfig /all' Command in Windows

• Open the Command Prompt.
• Type ipconfig /all and press Enter.
• This command displays all current TCP/IP network configurations, including DNS servers assigned to your device.

Step 3: Employ 'nslookup' Command

• Open the Command Prompt.
• Execute the command nslookup <domain_name>, replacing <domain_name> with the desired site (e.g., nslookup www.example.com).
• This command queries the DNS to find the corresponding IP address, helping you verify DNS resolution.

Step 4: Capture DNS Queries with Wireshark

• Open Wireshark and start a new capture session.
• Filter the traffic using dns to monitor DNS queries.
• Initiate a nslookup command to see how the DNS request appears in the Wireshark capture.
• Analyze the details of the DNS transaction, including query and response packets.

Step 5: Explore DNS Cache

• DNS caching improves performance by storing resolved domain names locally.
• To view the DNS cache on Windows, run the command:

  ipconfig /displaydns
  

• This command shows cached entries and their expiration times.

Step 6: Modify the Hosts File

• The Hosts file allows you to manually map domain names to IP addresses.
• Locate the Hosts file at C:\Windows\System32\drivers\etc\hosts.
• Open the file in a text editor with administrative privileges.
• Add entries in the format:

  <IP_Address> <domain_name>
  

• Save the file to apply changes. This helps in overriding DNS for specific domains.

Step 7: Configure DNS in Cisco IOS

• Access your Cisco device's command line interface.
• Enter configuration mode by typing:

  configure terminal
  

• Set the DNS server with the command:

  ip name-server <IP_Address>
  

• Replace <IP_Address> with the DNS server's IP you want to use.

Step 8: Conduct DNS Demonstrations

• Run multiple nslookup commands to test different domain resolutions.
• Observe the output and DNS server responses.
• Use Wireshark to capture and analyze the DNS queries made during these demonstrations.

Step 9: Review Key DNS Commands

• Familiarize yourself with essential commands:
  • ipconfig /all: View network configuration
  • nslookup: Query DNS
  • ipconfig /displaydns: Show DNS cache
  • ping <domain_name>: Check connectivity and DNS resolution

Conclusion

In this tutorial, you learned about the fundamental concepts of DNS, essential commands for querying and configuring DNS, and how to capture and analyze DNS traffic. Familiarizing yourself with these tools and techniques is vital for anyone studying for the CCNA exam or working with network configurations. Next, consider practicing with hands-on labs or quizzes to reinforce your understanding of DNS concepts.