🧠 DNS (Domain Name System)

 

🧠 DNS (Domain Name System)

Top 5 Key Points

  1. Converts Domain Names to IP Addresses:
    DNS translates human-readable domain names (like www.google.com) into machine-readable IP addresses (like 142.250.190.4).

  2. Simplifies Networking:
    Users remember domain names instead of IPs — making internet navigation easier.

  3. Uses UDP Port 53:
    DNS queries and responses use UDP port 53 (sometimes TCP for large zone transfers).

  4. Hierarchical Structure:
    DNS is a distributed system with Root, Top-Level Domains (TLD) (like .com, .org), and Authoritative Servers.

  5. Can Be Local or Public:
    In enterprise networks, DNS servers are often local to resolve internal names; otherwise, public DNS (like Google’s 8.8.8.8) is used.

⚙️ Technical Summary

FeatureDescription
OSI LayerApplication Layer
Transport ProtocolUDP/TCP Port 53
Main FunctionName-to-IP Resolution
Server RoleResponds to DNS queries
Client RoleSends name resolution requests

🧰 Packet Tracer Lab – DNS Server Configuration

🎯 Goal:

Set up a DNS Server that resolves a website name (www.company.com) to its IP address and allows PCs to browse it.

🖥️ Network Topology

[PC1] ---- [Switch] ---- [Server0 (DNS + Web Server)]

IP Plan

DeviceInterfaceIP AddressRole
Server0NIC192.168.10.2DNS + Web Server
PC1NICDHCP or Static 192.168.10.10DNS Client
Gateway (optional)Router (192.168.10.1)Default Gateway

🪜 Step-by-Step Configuration

🔹 1. Configure Server IP

On Server0:

  • Go to Desktop → IP Configuration

  • Set:

    IP Address: 192.168.10.2
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.10.1

🔹 2. Enable DNS Service

On Server0:

  1. Click Services → DNS

  2. Turn DNS Service: ON

  3. Under Resource Records, add:

    Name: www.company.com
Type: A
Address: 192.168.10.2

    ✅ This maps the domain name to the web server’s IP address.

🔹 3. Enable HTTP Service

  1. Go to Services → HTTP

  2. Turn HTTP Service: ON

  3. (Optional) Edit the HTML page to display a message like:

    Welcome to Company Website

🔹 4. Configure PC1 (Client)

On PC1:

  • Go to Desktop → IP Configuration

  • Set:

    IP Address: 192.168.10.10
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.10.1
DNS Server: 192.168.10.2

🔹 5. Test DNS Resolution

On PC1 → Desktop → Web Browser

  • Type: www.company.com

✅ If configured correctly, the browser loads the web page from Server0.
💡 Packet Tracer will show the HTTP connection to 192.168.10.2 — proving DNS resolution works.

🧠 Learning Summary

ConceptDescription
DNS RoleResolves domain names to IPs
ProtocolUDP/TCP Port 53
Record TypeA Record (name-to-IP mapping)
Server SetupEnable DNS service and add entries
Client SetupSet correct DNS server IP

💬 Teaching Tip

“DNS is like your phone’s contact list — you don’t remember everyone’s number (IP), just their names. The list (DNS) does the translation for you.”

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