Secure Your Network with the Uncomplicated Firewall

Uncomplicated Firewall

Uncomplicated Firewall, also known as ufw, is a convenient and beginner-friendly way to enforce OS-level firewall rules. For those who are hosting servers or any device that is accessible to the world (i.e., by public IP or domain name), it's critical that a firewall is properly implemented and active.

Ufw is available by default in all Ubuntu installations after 8.04 LTS. For other distributions, you can look to install ufw or check if there are alternative firewalls installed already. There are usually alternatives available, such as Fedora's firewall and the package available on most distributions: iptables. Ufw is considered a beginner-friendly front-end to iptables.

Gufw is available as a graphical user interface (GUI) application for users who are uncomfortable setting up a firewall through a terminal.

Getting Help

If you need help figuring out commands, remember that you can run the --help flag to get a list of options.

sudo ufw --help

Set Default State

The proper way to run a firewall is to set a strict default state and slowly open up ports that you want to allow. This helps prevent anything malicious from slipping through the cracks. The following command prevents all incoming traffic (other than the rules we specify later), but you can also set this for outgoing connections, if necessary.

sudo ufw default deny incoming

You should also allow outgoing traffic if you want to allow the device to communicate back to you or other parties. For example, media servers like Plex need to be able to send out data related to streaming the media.

sudo ufw default allow outgoing

Adding Port Rules

Now that we've disabled all incoming traffic by default, we need to open up some ports (or else no traffic would be able to come in). If you need to be able to ssh into the machine, you'll need to open up port 22.

sudo ufw allow 22

You can also issue more restrictive rules. The following rule will allow ssh connections only from machines on the local subnet.

sudo ufw allow proto tcp from 192.168.0.0/24 to any port 22

If you need to set a rule that isn't tcp, just append your connection type to the end of the rule.

sudo ufw allow 1900/udp

Enable ufw

Now that the firewall is configured and ready to go, you can enable the firewall.

sudo ufw enable

A restart may be required for the firewall to begin operating.

sudo reboot now

Checking Status

Now that the firewall is enabled, let's check and see what the rules look like.

sudo ufw status numbered

Status: active

     To                    Action      From
     --                    ------      ----
[ 1] 22                    ALLOW IN    Anywhere
[ 2] 22 (v6)               ALLOW IN    Anywhere (v6)

Deleting Rules

If you need to delete a rule, you need to know the number associated with that rule. Let's delete the first rule in the table above. You'll be asked to confirm the deletion as part of this process.

sudo ufw delete 1

Managing App Rules

Luckily, there's a convenient way for installed applications to create files that ufw can easily implement so that you don't have to search and find which ports your application requires. To see if your device has any applications with pre-installed ufw rules, execute the following command:

sudo ufw app list

The results should look something like this:

Available applications:
    OpenSSH
    Samba
    plexmediaserver
    plexmediaserver-all
    plexmediaserver-dlna

If you want to get more information on a specific app rule, use the info command.

sudo ufw app info plexmediaserver-dlna

You'll get a blurb of info back like this:

Profile: plexmediaserver-dlna
Title: Plex Media Server (DLNA)
Description: The Plex Media Server (additional DLNA capability only)

Ports:
    1900/udp
    32469/tcp

You can add or delete app rules the same way that you'd add or delete specific port rules.

sudo ufw allow plexmediaserver-dlna

sudo ufw delete RULE|NUM

Creating App Rules

If you'd like to create you own app rule, you'll need to create a file in the /etc/ufw/applications.d directory. Within the file you create, you need to make sure the content is properly formatted.

For example, here are the contents my plexmediaserver file, which creates three distinct app rules for ufw:

[plexmediaserver]
title=Plex Media Server (Standard)
description=The Plex Media Server
ports=32400/tcp|3005/tcp|5353/udp|8324/tcp|32410:32414/udp

[plexmediaserver-dlna]
title=Plex Media Server (DLNA)
description=The Plex Media Server (additional DLNA capability only)
ports=1900/udp|32469/tcp

[plexmediaserver-all]
title=Plex Media Server (Standard + DLNA)
description=The Plex Media Server (with additional DLNA capability)
ports=32400/tcp|3005/tcp|5353/udp|8324/tcp|32410:32414/udp|1900/udp|32469/tcp

So, if I wanted to create a custom app rule called "mycustomrule," I'd create a file and add my content like this:

sudo nano /etc/ufw/applications.d/mycustomrule

[mycustomrule]
title=My Custom Rule
description=This is a temporary ufw app rule.
ports=88/tcp|9100/udp

Then, I would just enable this rule in ufw.

sudo ufw allow mycustomrule