Difference between revisions of "Operating Systems/Linux/Ubuntu/Ubuntu 16.04 LTS/Firewalls"

Latest revision as of 21:31, 10 April 2025

Why?[edit | edit source]

Firewalls are critical for secure computer usage as prevent unwanted (and potentially malicious) connections from being made.

UFW standing for Uncomplicated FireWall, is the integrated firewall in all versions of Ubuntu 8.04 LTS and later; it has a graphical element (GUFW) that is also available for use. It is a firewall configuration tool running on top of iptables. UFW is a powerful tool that can greatly improve the security of your servers when properly configured.

How to configure[edit | edit source]

Status[edit | edit source]

To check if ufw is enabled, run:

sudo ufw status Output: Status: inactive The output will indicate if your firewall is active or not.

Enabling[edit | edit source]

If you got Status: inactive message when running ufw status, it means the firewall is not yet enabled on the system. You’ll need to run this command to enable it:

sudo ufw enable

Disabling[edit | edit source]

If you need to disable UFW, you can do so with the following command:

sudo ufw disable

Be aware that this command will fully disable the firewall service on the system.

Blocking an IP[edit | edit source]

To block all network connections that originate from a specific IP address, run the following command, replacing the IP address with the IP address that you want to block:

sudo ufw deny from 203.0.113.100

Output Rule added

In this example, from 203.0.113.100 specifies a source IP address of (enter IP address here).

If you run sudo ufw status now, you’ll see the specified IP address listed as denied:

Output Status: active

To Action From -- ------ ---- Anywhere DENY 203.0.113.100 All connections, coming in or going out, are blocked for the specified IP address.

Blocking a subnet[edit | edit source]

If you need to block a full subnet, you may use the subnet address as from parameter on the ufw deny command. This would block all IP addresses in the example subnet 203.0.113.0/24:

sudo ufw deny from 203.0.113.0/24

Output: Rule added

Allowing an IP adress[edit | edit source]

To allow all network connections that originate from a specific IP address, run the following command, replacing the highlighted IP address with the IP address that you want to allow access:

sudo ufw allow from (enter IP address here)

Output

Rule added

If you run sudo ufw status now, you’ll see output similar to this, showing the word ALLOW next to the IP address you just added.

Output Status: active

To Action From -- ------ ---- ... Anywhere ALLOW 203.0.113.101 You can also allow connections from a whole subnet by providing the corresponding subnet mask for a host, such as 203.0.113.0/24.

GUI[edit | edit source]

Press Alt+F2 and run GUFW, pass the authentication check
Turn the status slider to "on"

CLI[edit | edit source]

open the terminal
sudo ufw enable
you can use ufw -help to find other commands for further customization

@@ Line 37: / Line 37: @@
 <code>Rule added</code>
-In this example, from 203.0.113.100 specifies a source IP address of “203.0.113.100”.
+In this example, from 203.0.113.100 specifies a source IP address of (enter IP address here).
 If you run <code>sudo ufw</code> status now, you’ll see the specified IP address listed as denied:
@@ Line 60: / Line 60: @@
 To allow all network connections that originate from a specific IP address, run the following command, replacing the highlighted IP address with the IP address that you want to allow access:
-<code>sudo ufw allow from 203.0.113.101
+<code>sudo ufw allow from (enter IP address here)</code>
-Output
-Rule added</code>
+<code>Output</code>
+<code>Rule added</code>
 If you run <code>sudo ufw status</code> now, you’ll see output similar to this, showing the word ALLOW next to the IP address you just added.
@@ Line 74: / Line 76: @@
 Anywhere                   ALLOW       203.0.113.101
 You can also allow connections from a whole subnet by providing the corresponding subnet mask for a host, such as 203.0.113.0/24.
-==== Delete Rules ====
-Delete UFW Rule
-To delete a rule that you previously set up within UFW, use ufw delete followed by the rule (allow or deny) and the target specification. The following example would delete a rule previously set to allow all connections from an IP address of 203.0.113.101:
-sudo ufw delete allow from 203.0.113.101
-Output
-Rule deleted
-Another way to specify which rule you want to delete is by providing the rule ID. This information can be obtained with the following command:
-sudo ufw status numbered
-Output
-Status: active
-     To                         Action      From
-     --                         ------      ----
-[ 1] Anywhere                   DENY IN     203.0.113.100
-[ 2] Anywhere on eth0           ALLOW IN    203.0.113.102
-From the output, you can see that there are two active rules. The first rule, with highlighted values, denies all connections coming from the IP address 203.0.113.100. The second rule allows connections on the eth0 interface coming in from the IP address 203.0.113.102.
-Because by default UFW already blocks all external access unless explicitly allowed, the first rule is redundant, so you can remove it. To delete a rule by its ID, run:
-sudo ufw delete 1
-You will be prompted to confirm the operation and to make sure the ID you’re providing refers to the correct rule you want to delete.
-Output
-Deleting:
- deny from 203.0.113.100
-Proceed with operation (y|n)? y
-Rule deleted
-If you list your rules again with sudo ufw status, you’ll see that the rule was removed.
 ==== GUI ====