How to open TCP port in Debian 12

Before starting, make sure you have root or sudo privileges on your Debian 12 system. We’ll walk through the basic steps to open a TCP port using ufw and iptables, depending on which firewall you use.

Step 1: Check if UFW is Installed

UFW (Uncomplicated Firewall) is not enabled by default in Debian. First, check if it’s installed:

sudo ufw status

If you get a “command not found” error, install it with:

sudo apt update
sudo apt install ufw

Step 2: Enable UFW (If Not Already Enabled)

To make sure UFW is active:

sudo ufw enable

This will activate the firewall. Existing connections are not interrupted.

Step 3: Open the Desired TCP Port

For example, to open TCP port 8080, run:

sudo ufw allow 8080/tcp

You can replace 8080 with any port number you need.

To verify:

sudo ufw status numbered

You should see a rule allowing traffic to that port.

Step 4: Using iptables (If Not Using UFW)

If your system doesn’t use UFW and you’re managing firewall rules manually, use iptables.

To open TCP port 8080:

sudo iptables -A INPUT -p tcp --dport 8080 -j ACCEPT

To make it persistent after reboot, install the iptables-persistent package:

sudo apt install iptables-persistent
sudo netfilter-persistent save

Step 5: Check if Port is Open and Listening

After adding the rule, make sure the port is actually open and the service is running on it:

sudo ss -tuln | grep 8080

If nothing shows up, your firewall rule may be fine but no service is using the port yet. And that’s it — your TCP port should now be open on Debian 12.