DNS Basics

Understanding the Domain Name System and how it powers internet navigation.

Table of contents

1. What is DNS?
2. How DNS Works
   1. 1. The DNS Query Process
3. DNS Record Types
4. Hands-On DNS Tools
   1. Using nslookup
5. Common DNS Issues
   1. 1. DNS Resolution Failures
   2. 2. Troubleshooting Steps
   3. 3. Solutions
6. DNS Security
   1. DNSSEC (DNS Security Extensions)
7. Best Practices
8. Next Steps
9. Additional Resources

What is DNS?

DNS (Domain Name System) acts like the internet’s phone book, translating human-readable domain names (like www.google.com) into IP addresses (like 142.250.190.78) that computers use to identify each other.

The step-by-step process of DNS resolution

📝 Why DNS Matters

Without DNS, you'd need to remember IP addresses for every website you want to visit, making the internet much harder to use.

How DNS Works

1. The DNS Query Process

When you type a website address in your browser:

1. Local DNS Cache Check
   • Your computer first checks its local DNS cache
   • Recently visited sites are stored here for quick access
2. Recursive DNS Server
   • If not in cache, query goes to your ISP’s DNS server
   • This server starts the recursive lookup process
3. Root DNS Servers
   • Query first goes to root servers (.)
   • They direct to the correct top-level domain servers
4. Top-Level Domain (TLD) Servers
   • Handles domains like .com, .org, .net
   • Points to authoritative name servers
5. Authoritative Name Servers
   • Contains the actual DNS records
   • Returns the IP address for the domain

❗ DNS Caching

DNS servers cache results to speed up future requests and reduce network traffic.

DNS Record Types

Common DNS record types include:

Record Type	Purpose	Example
A	Maps domain to IPv4	example.com → 93.184.216.34
AAAA	Maps domain to IPv6	example.com → 2606:2800:220:1:248:1893:25c8:1946
CNAME	Creates domain alias	www.example.com → example.com
MX	Specifies mail servers	Mail handled by mail.example.com
TXT	Text information	SPF, DKIM records

Hands-On DNS Tools

Using nslookup

# Basic DNS lookup
nslookup google.com

# Check mail servers
nslookup -type=mx gmail.com

# Query specific DNS server
nslookup google.com 8.8.8.8

💡 Practice Exercise

Try looking up different types of DNS records for your favorite websites using nslookup.

Common DNS Issues

1. DNS Resolution Failures

• “DNS Server Not Responding”
• “This site can’t be reached”
• Slow website loading

2. Troubleshooting Steps

# Clear DNS cache (Windows)
ipconfig /flushdns

# Check DNS servers
ipconfig /all

# Test DNS resolution
nslookup google.com

3. Solutions

• Clear DNS cache
• Check network connection
• Try alternative DNS servers (e.g., 8.8.8.8)
• Contact ISP if persistent

DNS Security

⚠️ Security Note

DNS poisoning and spoofing attacks can redirect users to malicious websites. Always ensure your DNS settings are from trusted sources.

DNSSEC (DNS Security Extensions)

• Adds security to DNS lookups
• Verifies DNS data integrity
• Prevents DNS spoofing

Best Practices

1. Use Reliable DNS Servers
   • Your ISP’s servers
   • Public DNS (Google: 8.8.8.8, Cloudflare: 1.1.1.1)
2. Regular Maintenance
   • Clear DNS cache periodically
   • Update DNS settings when needed
   • Monitor DNS response times
3. Security Considerations
   • Use DNSSEC when available
   • Monitor for unusual DNS behavior
   • Keep DNS software updated

Next Steps

Continue to DHCP Basics to learn how devices obtain their network configurations automatically.

Additional Resources

• DNS troubleshooting guide
• Common DNS commands
• Command Cheatsheet