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HETVI UNDHAD
HETVI UNDHAD

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DNS

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🌐 Understanding DNS (Domain Name System): The Internet’s Phonebook
The Domain Name System (DNS) is one of the most crucial components of the internet. Without it, browsing the web would be much harder. Instead of typing www.example.com, we’d be stuck memorizing long strings of numbers like 192.168.1.2.
In this blog, we’ll dive into what DNS is, how it works, its message structure, record types, and even simulate DNS queries using Cisco Packet Tracer.

🔎 1. What is DNS?
DNS stands for Domain Name System. Its primary purpose is to translate human-readable domain names into machine-readable IP addresses.
Think of it as the phonebook of the internet — instead of remembering phone numbers, you just look up a name. Similarly, DNS allows you to type a website’s name instead of its IP address.

✨ Key Features of DNS
• Human-friendly domain names
• Fast and efficient IP resolution
• Distributed database system (not centralized)
• Scalable and fault-tolerant

🖥 2. DNS Services and Records
DNS is made up of different types of servers and uses various record types to function properly.
DNS Server Types

  1. Authoritative DNS Server – Stores and serves the actual records of a domain.

  2. Recursive Resolver – Accepts client queries and finds the answer by asking other DNS servers.

  3. Caching DNS Server – Saves recently resolved queries in memory to make future lookups faster.
    Common DNS Record Types
    • A Record → Maps a domain name to an IPv4 address
    • AAAA Record → Maps a domain name to an IPv6 address
    • CNAME Record → Alias of one domain to another (e.g., blog.example.com → www.example.com)
    • MX Record → Identifies mail servers for a domain
    • NS Record → Specifies the authoritative name servers for a domain
    • PTR Record → Used for reverse DNS lookup (IP → domain)

📡 3. DNS Protocol Basics
DNS runs on the Application Layer of the OSI model and uses both UDP and TCP depending on the situation.
• Port: 53
• Transport Protocol:
o UDP (default, faster, used for most queries)
o TCP (used for zone transfers or responses larger than 512 bytes)
Query Types
• Recursive Query → Client asks DNS to fully resolve the name
• Iterative Query → DNS server responds with the best answer it has or refers to another server
TTL (Time To Live)
Defines how long a record stays in cache before it needs to be refreshed.

📑 4. DNS Message Format (Header Fields)
A DNS message contains both queries and responses, structured into specific fields:
• Transaction ID – Unique identifier for matching queries & responses
• Flags – Includes query/response type, authoritative answer flag, recursion, etc.
• Questions – Number of queries sent
• Answers – Number of answers returned
• Authority – Reference to authoritative servers
• Additional Info – Extra helpful records
📖 Learn more from IETF RFC 1035

🛠️ 5. Practical Demonstration in Cisco Packet Tracer
One of the best ways to understand DNS in action is to simulate it in Cisco Packet Tracer:

  1. Create a network topology with a DNS server, client PC, and a router.

  2. Configure the DNS server with an A record for a domain (e.g., www.mywebsite.com → 192.168.1.10).

  3. On the client PC, configure the DNS server IP in the network settings.

  4. Ping or open the domain name in the browser → it will resolve to the correct IP address.
    👉 Cisco Packet Tracer Download (Official)

📚 References & Further Reading
• How DNS Works – Cloudflare
• IETF RFC 1035 – DNS Specifications
• DNS in Depth – ICANN

🛠5. DNS Configuration in Cisco Packet Tracer
You can easily simulate DNS in Cisco Packet Tracer by following these steps:

Step 1: Place Devices
• PC1 → Client
• PC2 → DNS Server
• Switch → Connect both PCs

Step 2: Configure IP Addresses
Assign static IPs to all devices within the same subnet.
Example configuration:
• PC1 (Client): 192.168.1.10
• PC2 (DNS Server): 192.168.1.2

Step 3: Configure DNS Server

  1. Select PC2 (DNS Server) → Services Tab → DNS
  2. Add DNS entries: o www.example.com → 192.168.1.2 o www.test.com → 192.168.1.3 ________________________________________ Step 4: Configure Client
  3. Go to PC1 → Desktop Tab → IP Configuration
  4. Set the DNS Server IP to 192.168.1.2 ________________________________________ Step 5: Test DNS Resolution
  5. Open Command Prompt on PC1
  6. Run the command: ping www.example.com ✅ Result: The domain www.example.com resolves to 192.168.1.2 ________________________________________ This simple simulation demonstrates how DNS translates domain names into IP addresses within a local network environment.

** FOR BETTER UNDERSTANDING REFER THIS**

Final Thoughts
The Domain Name System (DNS) is truly the backbone of the internet. From simple browsing to sending emails, DNS makes everything possible by seamlessly translating domain names into IP addresses.
Next time you type a URL in your browser, remember — there’s a whole system working behind the scenes to get you where you want to go!

Prepared by hetvi undhad (24CE131),siya thakkar (24CE125).

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