iptables is the classic Linux firewall utility that provides fine-grained packet filtering and NAT. While Ubuntu uses UFW as a front-end by default, understanding iptables rules is essential for advanced network control on Ubuntu 24.04 LTS.

Tested and valid on:

Ubuntu 24.04 LTS

Prerequisites

Ubuntu 24.04 LTS server
A user with sudo privileges
Basic understanding of networking and IP addresses

Step 1 – View Current Rules

List all current iptables rules:

sudo iptables -L -n -v
sudo iptables -t nat -L -n -v

Step 2 – Set Default Policies

Set the default drop policy (do this carefully — it will block all traffic):

sudo iptables -P INPUT DROP
sudo iptables -P FORWARD DROP
sudo iptables -P OUTPUT ACCEPT

Step 3 – Allow Established Connections and Loopback

Allow existing connections and localhost traffic:

sudo iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A INPUT -i lo -j ACCEPT

Step 4 – Allow SSH

Allow SSH connections (change port if needed):

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

Step 5 – Allow HTTP and HTTPS

Allow web traffic:

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

Step 6 – Block an IP Address

Drop all traffic from a specific IP:

sudo iptables -A INPUT -s 203.0.113.100 -j DROP

Step 7 – Save Rules Persistently

Install iptables-persistent to save rules across reboots:

sudo apt install iptables-persistent -y
sudo netfilter-persistent save
sudo netfilter-persistent reload

View saved rules:

sudo cat /etc/iptables/rules.v4

Conclusion

iptables rules are now configured on Ubuntu 24.04 LTS. For simpler management, UFW wraps iptables in an easy-to-use interface. Use raw iptables for complex routing, NAT, and port forwarding scenarios.

How to Configure iptables Firewall Rules on Ubuntu 24.04