Welcome to Day 43 of my Networking & Security journey! 🚀 Today, I explored four core networking concepts that power the internet and practiced firewall configuration hands-on.

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🌍 1. DNS (Domain Name System)

• Definition: DNS translates human-readable domain names (e.g., google.com) into IP addresses (e.g., 142.250.182.78) so computers can communicate.

• How it works:

  1. You type example.com in a browser.

  2. A DNS resolver queries a DNS server.

  3. The server responds with the correct IP address.

  4. Your browser connects to that IP.

🔑 Types of DNS Records:

• A Record: Maps a domain → IPv4 address.

• AAAA Record: Maps a domain → IPv6 address.

• CNAME: Alias for another domain.

• MX Record: Mail exchange (used for email).

💡 Analogy: Think of DNS as the phonebook of the internet.

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📡 2. DHCP (Dynamic Host Configuration Protocol)

• Definition: A network protocol that automatically assigns IP addresses and other network settings to devices.

• Why it’s needed: Without DHCP, every device would need to be manually configured.

• How it works (DORA Process):

  1. Discover → Client broadcasts to find DHCP server.

  2. Offer → DHCP server replies with an available IP.

  3. Request → Client requests the offered IP.

  4. Acknowledge → DHCP server confirms the assignment.

💡 Analogy: Imagine entering a parking lot where the guard (DHCP server) assigns you an empty parking spot (IP address).

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🌐 3. NAT (Network Address Translation)

• Definition: NAT allows multiple devices in a private network (e.g., 192.168.x.x) to share a single public IP when accessing the internet.

• Types of NAT:

  • Static NAT: One private ↔ One public IP.

  • Dynamic NAT: Many private ↔ Many public IPs (from a pool).

  • PAT (Port Address Translation): Many private ↔ One public IP (most common, e.g., your home Wi-Fi).

💡 Real-life Example: Your home Wi-Fi has multiple devices, but the ISP sees only one public IP.

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🔥 4. Firewalls

A firewall is a security system that monitors and controls incoming and outgoing traffic based on defined rules.

• Types of Firewalls:

  • Hardware Firewall: Dedicated device (e.g., routers with firewall).

  • Software Firewall: Installed on operating systems (Linux ufw, iptables).

💡 Analogy: Think of a firewall as a security guard who checks ID cards before letting people (packets) enter a building (network).

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🛠 Hands-on Practice

Using ufw (Uncomplicated Firewall)

# Enable UFW
sudo ufw enable

# Check status
sudo ufw status verbose

# Allow SSH (port 22)
sudo ufw allow 22

# Allow HTTP (port 80)
sudo ufw allow 80/tcp

# Deny a specific port (e.g., 23 - Telnet)
sudo ufw deny 23

# Delete a rule
sudo ufw delete allow 80/tcp

Using iptables (Advanced Firewall Rules)

View existing rules

sudo iptables -L -v

Allow incoming HTTP traffic (port 80)

sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT

Block incoming traffic from a specific IP

sudo iptables -A INPUT -s 192.168.1.100 -j DROP

Allow SSH from a specific subnet

sudo iptables -A INPUT -p tcp -s 192.168.1.0/24 --dport 22 -j ACCEPT

Drop all incoming connections by default

sudo iptables -P INPUT DROP

Save iptables rules (Debian/Ubuntu)

sudo sh -c "iptables-save > /etc/iptables/rules.v4"

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👨‍💻 Author

Ritesh Singh
🌐 LinkedIn | 📝 Hashnode | GitHub

#100DaysOfDevOps #CICD #GitHubActions #DevOps #Beginner #100DaysOfDevOps #Networking #Security #Linux #CloudComputing #Firewalls #DNS #DHCP #NAT