ufw to configure Linux firewall

So this website is running on an Ubuntu virtual machine. It's obviously important to configure firewall policy to limit malignant traffics. Linux comes built-in with iptables but it looks rather difficult to configure. So that's why I use ufw. Note, ufw is not the firewall itself. It's a configuration tool. iptables is still the firewall.

First all, let's install ufw by:

sudo apt install ufw

You are probably connecting to your ubuntu server by SSH. So please make sure that you turn on port 22 by:

sudo ufw allow 22

Please note that by default, ufw blocks ALL traffics. So please definitely turn on the port you need to connect to your server before you enable it. Ask me how I learned that.

Your iptables rules may still work behind the scenes. It's not a bad idea to purge all of them by running the following comments one at a time:

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

Now you can enable ufw. Again, double check and make sure that you did allow SSH before the comment below:

sudo ufw enable

Anytime you want to check the status of ufw, you can 

sudo ufw status

If you want to turn off ufw, you certainly can. But why?

sudo ufw disable

Let's say you want to enable port 80 and port 443 for HTTP and HTTPS, sure, as below:

sudo ufw allow 80
sudo ufw allow 443

You obviously can just allow traffics from a single IP. Let's say I want to allow HTTP from just IP 8.8.8.8 because that's my home IP (yeah, right, ). I'm still testing my server, after all. No problem. Do as this (you may want to disable 80 traffics from all IPs first, if it's on):

sudo ufw delete allow 80
sudo ufw allow from 8.8.8.8 to any port 80

Or you want to allow traffics from multiple IPs but not the entire internet. Let's do this:

sudo ufw allow from 192.168.0.0/16 to any port 80

This should allow HTTP traffics to IPs 192.168.0.1 to 192.168.255.254. This is typically your entire home intranet.

Anytime you want to remove a rule, just put the word "delete" between "ufw" and "allow". For 2 examples below:

sudo ufw delete allow 80
sudo ufw delete allow from 192.168.0.0/16 to any port 80

This is about it. Very simple and elegant. Please let me know if you have questions.

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