Uncomplicated Firewall (UFW) is a simplified firewall management interface that hides the complexity of lower-level packet filtering technologies such
uftables. Let’s learn how to set up a firewall with UFW on Ubuntu server.
Using IPv6 with 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
nano or your favourite editor:
sudo nano /etc/default/ufw
Then make sure the value of
yes. It should look like this:
Save and close the file. Now, when UFW is enabled, it will be configured to write both IPv4 & IPv6 firewall rules. However, 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.
Setting up default policies
By default, UFW is set to deny all incoming connections and allow all outgoing connections. This means anyone trying to reach your server would not be able to connect, while any application within the server would be able to reach the outside world.
If you have already edited UFW, you can set the defaults used by UFW, use these commands:
sudo ufw default deny incoming
sudo ufw default allow outgoing
These firewall defaults alone might suffice for a personal computer, but servers typically need to respond to incoming requests from outside users.
Allowing SSH connections
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 command:
This will create firewall rules that will allow all connections on port
22, which is the port that the SSH daemon listens on by default. UFW knows what port
allow ssh means because it’s listed as a service in the
However, 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:
If you configured you 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:
Now that your firewall is configured to allow incoming SSH connections, we can enable it.
To enable UFW, use this command:
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 and hit ENTER.
The firewall is now active. Run the
sudo ufw status verbose command to see the rules that are set.
Allowing other connections
At this point, you should allow all of the other connections that your server needs to respond to. The connections that you should allow depends on 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. You can also do this for:
- HTTP on port
sudo ufw allow http or
sudo ufw allow 80
- HTTPS on port
sudo ufw allow https or
sudo ufw allow 443
There are several others ways to allow other connections, aside from specifying a port or known service.
Specific port ranges
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
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 (
udp) that the rules should apply to. We haven’t mentioned this before because not specifying the protocol automatically allows both protocols, which is OK in most cases.
Specific IP addresses
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
184.108.40.206, you need to specify
from, then the IP address:
sudo ufw allow from 220.127.116.11
You can also specify a specific port that the IP address is allowed to connect to by adding
to any port followed by the port number. For example, if you want to allow
18.104.22.168 to connect to port
22, use this command:
sudo ufw allow from 22.214.171.124 to any port 22
If you want to allow a subnet of IP addresses, you can do so using CIDR notation to specify a net mask. For example, if you want to allow all ot the IP addresses ranging from
126.96.36.199 you could use this command:
sudo ufw allow 188.8.131.52/24
Likewise, you may also specify the destination port that the subnet
184.108.40.206/24 is allowed to connect to. Again, we’ll use port
22 as an example:
sudo ufw allow from 220.127.116.11/24 to any port 22
Connection to a specific network interface
If you want to create a firewall rule that only applies to a specific network interface, you can do so by specifying “allow in on” followed by the name of the network interface.
You may want to look up your network interfaces before continuing. To do so, use this command:
The output indicates the network interface names. They are typically named something like
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state
. . .
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
. . .
So, if your server has a public network interface called
eth0, you could allow HTTP traffic (port
80) to it with this command:
sudo ufw allow in on eth0 to any port 80
Doing so would allow your server to receive HTTP requests from the public internet.
Or, if you want your MySQL database server (port
3306) to listen for connections on the private network interface
eth1, for example, you could use this command:
sudo ufw allow in on eth1 to any port 3306
This would allow other servers on you private network to connect your MySQL database.
If you haven’t changed the default policy for incoming connections, UFW is configured to deny all incoming connections. Generally, this simplifies the process of creating a secure firewall policy by requiring you to create rules that explicitly allow specific ports and IP addresses through.
However, sometimes you will want to deny specific connections based on the source IP address or subnet, perhaps because you know that your server is being attacked from there. Also, if you want to change your default incoming policy to allow (which is not recommended), you would need to create deny rules for any services or IP addresses that you don’t want to allow connections for.
For example, to deny HTTP connections, you could use this command:
Or, if you want to deny all connections from
18.104.22.168 you could use this command:
sudo ufw deny from 22.214.171.124
Knowing how to delete firewall rules is just as important as knowing how to create them. There are two different ways to specify which rules de delete: by rule number or by the actual rule.
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:
To Action From
-- ------ ----
[ 1] 22 ALLOW IN 126.96.36.199/24
[ 2] 80 ALLOW IN Anywhere
If we decide that we want to delete rule 2, the one that allows port 80 connections, we can specify it in a UFW delete command like this:
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.
Checking UFW status and rules
At any time, you can check the status of UFW with this command:
If UFW is disabled, which it is by default, you’ll see something like this:
If UFW is active, the output might look something like this:
Logging: on (low)
Default: deny (incoming), allow (outgoing), disabled (routed)
New profiles: skip
To Action From
-- ------ ----
22/tcp ALLOW IN Anywhere
status command if you want to check how UFW has configured the firewall.
Disabling or resetting UFW
If you decide to disable UFW, doing so with this command:
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:
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.
Your firewall is now configured to allow specific connections. Be sure to allow any other incoming connections that your server needs, while limiting any unnecessary connections, so your server will be functional and secure.