Blocking Access to Private Networks on Ubuntu Using UFW

8 min readUpdated December 2, 2025

You may suddenly start receiving complaints from the data center about private network scanning even though you did not intend to do this. To prevent such outbound connections, you can block private networks with the ufw firewall.

#Installing ufw

First, check whether ufw is installed on your server and install it if needed.

bash

sudo apt install ufw

Before enabling the firewall, open the required ports so you do not lose access to your services. In most cases, you should allow SSH, HTTP, and HTTPS.

bash

sudo ufw allow 22
sudo ufw allow 80
sudo ufw allow 443

After that, enable the firewall.

bash

sudo ufw enable

You can check the current firewall status with the following command.

bash

sudo ufw status

#Blocking private networks

Now you can block private networks to prevent any outbound connections to them from your server.

The following ranges are treated as private or special-use networks:

10.0.0.0/8

172.16.0.0/12

192.168.0.0/16

100.64.0.0/10

198.18.0.0/15

169.254.0.0/16

To block these ranges, add the following rules.

bash

sudo ufw deny out from any to 10.0.0.0/8
sudo ufw deny out from any to 172.16.0.0/12
sudo ufw deny out from any to 192.168.0.0/16
sudo ufw deny out from any to 100.64.0.0/10
sudo ufw deny out from any to 198.18.0.0/15
sudo ufw deny out from any to 169.254.0.0/16

After adding the rules, verify that they are present.

bash

sudo ufw status

# Or use iptables
iptables-save

If you try to access an address from a blocked range, the connection will fail. For example, you can test this with .

bash

ping 198.18.22.62

This completes the private network blocking setup.

#Unblocking networks if required

If you later need to restore access to one of the blocked networks, first display the numbered list of current ufw rules.

bash

sudo ufw status numbered

Then delete the required rule by its number. Replace with the actual number from the previous command output.

bash

sudo ufw delete N

For example, you can remove rule 7.

bash

sudo ufw delete 7

After removing the rule, access to the corresponding address will no longer be restricted.

You now know how to block and unblock your server access to private networks with ufw.

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