UFW, or Uncomplicated Firewall, is an interface to iptables that is geared towards simplifying the process of configuring a firewall. While iptables is a solid and flexible tool, it can be difficult for beginners to learn how to use it to properly configure a firewall. If you're looking to get started securing your network, and you're not sure which tool to use, UFW may be the right choice for you.
This tutorial will show you how to set up a firewall with UFW on Ubuntu 14.04.
Before you start using this tutorial, you should have a separate, non-root superuser account—a user with sudo privileges—set up on your Ubuntu server. You can learn how to do this by completing at least steps 1-3 in the Initial Server Setup with Ubuntu 14.04 tutorial.
UFW is installed by default on Ubuntu. If it has been uninstalled for some reason, you can install it with apt-get:
sudo apt-get install ufw
If your Ubuntu server has IPv6 enabled, ensure that UFW is configured to support IPv6 so that it will manage firewall rules for IPv6 in addition to IPv4. To do this, open the UFW configuration with your favorite editor. We'll use nano:
sudo nano /etc/default/ufw
Then make sure the value of "IPV6" is to equal "yes". It should look like this:
/etc/default/ufw excerpt
...
IPV6=yes
...
Save and quit. Hit Ctrl-X to exit the file, then Y to save the changes that you made, then ENTER to confirm the file name.
When UFW is enabled, it will be configured to write both IPv4 and IPv6 firewall rules.
This tutorial is written with IPv4 in mind, but will work fine for IPv6 as long as you enable it.
Check UFW Status and Rules
At any time, you can check the status of UFW with this command:
sudo ufw status verbose
By default, UFW is disabled so you should see something like this:
Output:
Status: inactive
If UFW is active, the output will say that it's active, and it will list any rules that are set. For example, if the firewall is set to allow SSH (port 22) connections from anywhere, the output might look something like this:
Output:
Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing), disabled (routed)
New profiles: skipTo Action From
-- ------ ----
22/tcp ALLOW IN Anywhere
Before enabling UFW, we will want to ensure that your firewall is configured to allow you to connect via SSH. Let's start with setting the default policies.
Set Up Default Policies
If you're just getting started with your firewall, the first rules to define are your default policies. These rules control how to handle traffic that does not explicitly match any other rules. By default, UFW is set to deny all incoming connections and allow all outgoing connections. This means anyone trying to reach your cloud server would not be able to connect, while any application within the server would be able to reach the outside world.
Let's set your UFW rules back to the defaults so we can be sure that you'll be able to follow along with this tutorial. To set the defaults used by UFW, use these commands:
sudo ufw default deny incoming
sudo ufw default allow outgoing
As you might have guessed, these commands set the defaults to deny incoming and allow outgoing connections. These firewall defaults, by themselves, might suffice for a personal computer but servers typically need to respond to incoming requests from outside users. We'll look into that next.
Allow SSH Connections
If we enabled our UFW firewall now, it would deny all incoming connections. This means that we will need to create rules that explicitly allow legitimate incoming connections—SSH or HTTP connections, for example—if we want our server to respond to those types of requests. If you're using a cloud server, you will probably want to allow incoming SSH connections so you can connect to and manage your server.
To configure your server to allow incoming SSH connections, you can use this UFW command:
sudo ufw allow ssh
We can actually write the equivalent rule by specifying the port instead of the service name. For example, this command works the same as the one above:
sudo ufw allow 22
If you configured your SSH daemon to use a different port, you will have to specify the appropriate port. For example, if your SSH server is listening on port 2222, you can use this command to allow connections on that port:
sudo ufw allow 2222
Now that your firewall is configured to allow incoming SSH connections, we can enable it.
Enable UFW
To enable UFW, use this command:
sudo ufw enable
You will receive a warning that says the "command may disrupt existing ssh connections." We already set up a firewall rule that allows SSH connections so it should be fine to continue. Respond to the prompt with y.
The firewall is now active. Feel free to run the sudo ufw status verbose command to see the rules that are set.
Allow Other Connections
Now you should allow all of the other connections that your server needs to respond to. The connections that you should allow depends your specific needs. Luckily, you already know how to write rules that allow connections based on a service name or port—we already did this for SSH on port 22.
We will show a few examples of very common services that you may need to allow. If you have any other services for which you want to allow all incoming connections, follow this format.
HTTP port 80
HTTP connections, which is what unencrypted web servers use, can be allowed with this command:
sudo ufw allow http
If you'd rather use the port number, 80, use this command:
sudo ufw allow 80
HTTPS connections, which is what encrypted web servers use, can be allowed with this command:
sudo ufw allow https
If you'd rather use the port number, 443, use this command:
sudo ufw allow 443
FTP connections, which is used for unencrypted file transfers (which you probably shouldn't use anyway), can be allowed with this command:
sudo ufw allow ftp
If you'd rather use the port number, 21, use this command:
sudo ufw allow 21/tcp
You can specify port ranges with UFW. Some applications use multiple ports, instead of a single port.
For example, to allow X11 connections, which use ports 6000-6007, use these commands:
sudo ufw allow 6000:6007/tcp
sudo ufw allow 6000:6007/udp
When specifying port ranges with UFW, you must specify the protocol (tcp or udp) that the rules should apply to. We haven't mentioned this before because not specifying the protocol simply allows both protocols, which is OK in most cases.
When working with UFW, you can also specify IP addresses. For example, if you want to allow connections from a specific IP address, such as a work or home IP address of 15.15.15.51, you need to specify "from" then the IP address:
sudo ufw allow from 15.15.15.51
Knowing how to delete firewall rules is just as important as knowing how to create them. There are two different ways specify which rules to delete: by rule number or by the actual rule (similar to how the rules were specified when they were created). We'll start with the delete by rule number method because it is easier, compared to writing the actual rules to delete, if you're new to UFW.
By Rule Number
If you're using the rule number to delete firewall rules, the first thing you'll want to do is get a list of your firewall rules. The UFW status command has an option to display numbers next to each rule, as demonstrated here
sudo ufw status numbered
Numbered Output:
Status: active
To Action From-- ------ ----
[ 1] 22 ALLOW IN 15.15.15.0/24
[ 2] 80 ALLOW IN Anywhere
If we decide that we want to delete rule 2, the one that allows port 80 (HTTP) connections, we can specify it in a UFW delete command like this:
sudo ufw delete 2
This would show a confirmation prompt then delete rule 2, which allows HTTP connections. Note that if you have IPv6 enabled, you would want to delete the corresponding IPv6 rule as well.
By Actual Rule
The alternative to rule numbers is to specify the actual rule to delete. For example, if you want to remove the "allow http" rule, you could write it like this:
sudo ufw delete allow http
You could also specify the rule by "allow 80", instead of by service name:
sudo ufw delete allow 80
This method will delete both IPv4 and IPv6 rules, if they exist.
How To Disable UFW (optional)
If you decide you don't want to use UFW for whatever reason, you can disable it with this command:
sudo ufw disable
Any rules that you created with UFW will no longer be active. You can always run sudo ufw enable if you need to activate it later.
If you already have UFW rules configured but you decide that you want to start over, you can use the reset command:
sudo ufw reset
This will disable UFW and delete any rules that were previously defined. Keep in mind that the default policies won't change to their original settings, if you modified them at any point. This should give you a fresh start with UFW.
Conclusion
Your firewall should now be configured to allow (at least) SSH connections. Be sure to allow any other incoming connections that your server, while limiting any unnecessary connections, so your server will be functional and secure.
To learn about more common UFW configurations, check out this tutorial: UFW Essentials: Common Firewall Rules and Commands
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