IP tables Installation And Configuration

🎯 Objective

Learn how to install, configure, and manage Linux firewall rules using iptables to control incoming and outgoing network traffic.

# 📘 What is iptables?

iptables is a command-line firewall utility used to manage network traffic rules in the Linux kernel.

It allows administrators to:

iptables works with the Linux Netfilter framework.

# 🔍 How iptables Works

iptables filters packets using rules organized into tables and chains.

Tables

Chains

# 📦 Install iptables

Most Linux systems already include iptables.

Install on RHEL / CentOS / Rocky Linux

sudo yum install iptables-services-y

Install on Ubuntu / Debian

sudo apt install iptables-y

# 🔎 Check iptables Status

List current rules:

sudo iptables-L

Detailed view:

sudo iptables-L-v-n

Explanation:

# 📊 View Rules with Line Numbers

sudo iptables-L--line-numbers

Useful when deleting specific rules.

# 🚀 Start iptables Service

sudo systemctl start iptables

Enable at boot:

sudo systemctl enable iptables

Check status:

sudo systemctl status iptables

# 🛡 Basic iptables Rules

Allow SSH traffic

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

Meaning:

Allow HTTP traffic

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

Allow HTTPS traffic

sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT

Block a specific IP

sudo iptables -A INPUT -s 192.168.1.100 -j DROP

Meaning:

Drop all traffic from that IP.

Allow localhost traffic

sudo iptables -A INPUT -i lo -j ACCEPT

Allow established connections

sudo iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

# ❌ Drop All Other Traffic

Set default policy:

sudo iptables -P INPUT DROP

Meaning:

All incoming traffic is blocked unless explicitly allowed.

# 🧹 Delete iptables Rules

Delete specific rule:

sudo iptables -D INPUT2

Delete by rule specification:

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

# 🔄 Flush All Rules

Remove all rules:

sudo iptables -F

Delete all chains:

sudo iptables -X

# 💾 Save iptables Rules

Rules disappear after reboot unless saved.

Save rules:

sudo service iptables save

or

sudo iptables-save > /etc/sysconfig/iptables

# 🔁 Restore Rules

sudo iptables-restore < /etc/sysconfig/iptables

# 🌐 Check Listening Ports

Useful when configuring firewall:

sudo ss-tulnp

# 🧪 Example Firewall Configuration

Allow only:

Block everything else.

sudo iptables -F

sudo iptables -A INPUT -i lo -j ACCEPT

sudo iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT

sudo iptables -P INPUT DROP

# ⚠ Common iptables Issues

Locked out from SSH

If SSH rule missing:

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

Always allow SSH before setting DROP policy.

Firewall rules lost after reboot

Fix:

Save rules:

sudo iptables-save

Service not running

Check:

sudo systemctl status iptables

# 📁 Important iptables Files

# 🧰 Useful iptables Commands

# 🔎 Example Troubleshooting

Web server not reachable

Check firewall:

sudo iptables -L

If port 80 blocked:

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

Restart service if needed.

# ✅ Key Learning Points