The firewall that Linux uses is called iptables. Different graphical shells are used so that configuration is easy. Think about one of them: Simple Firewall (UFW).
Short description
The name comes from English, and it literally means “simple firewall.” The product has a graphical shell that is based on the command line. This is one of its features. In short, UFW is used to set up simple firewalls. It has the bare minimum of functions needed to protect corporate resources in a standard way. More complex rules and fine tuning are available in iptables.
At first, the solution was made for the Debian and Ubuntu families of operating systems. Under Ubuntu, the following steps are taken.
Preliminary preparation
If UFW is not installed on the server platform, use the standard utility:
sudo apt-get install ufw
The second option – the utility is installed, but inactive, then we write:
sudo ufw enable
Important! Any actions related to product configuration are performed with superuser rights.
After installation, check the status of the program:
sudo ufw status verbose
The standard configuration of the program blocks incoming traffic, but allows outgoing traffic. To change the parameters, open the system file:
sudo nano /etc/default/ufw
sudo ufw default deny incoming
sudo ufw default allow outgoing
The first line is responsible for blocking, and the second for outgoing connections.
Setup
UFW distributes rules according to program profiles. They are stored in the following path:
/etc/ufw/applications.d
Creating a new or editing a current profile is carried out by the administrator in manual mode. First, let’s take a look at the current profiles:
sudo ufw app list
Viewing detailed information on any record is carried out using the following command:
sudo ufw app info 'name'
Where name is the profile name enclosed in single quotes.
For example, let’s look at the OpenSSH service:
The first line is the name of the new entry in UFW. The second describes the title by which the profile will be identified. The third contains a brief description of the service (it is recommended to use 1-2 sentences). The last line specifies the ports that need to be opened for the application to work.
Save the file and restart the firewall:
ufw reload
The next step is to write the policy for the new entry. Two modes are available: allow (Allow) and prohibit (Deny). The syntax looks like this:
ufw
Where action is one of the two values Allow or Deny and name_profile is the name of the profile.
Port operations
The Allow/Deny commands are also used to open/close ports, depending on the requirements of the administrator. The syntax looks like this:
sudo ufw
Decryption:
1. action – one of two actions: allow (Allow) or deny (Deny);
2. port – numeric name of the port for which the rule is applied;
3. name_protocol – the name of the protocol.
If you want to specify a list of ports, use a colon between the start and end points. An alternative is to use the name of the service for which the entry is being created. For example, let’s open a port for an HTTP service:
sudo ufw allow http
Important! UFW allows a standard port that is assigned to a service. If the value differs from the generally accepted ones, then you cannot create a rule by the name of the service – it is not activated.
Operations with IP addresses
Similarly to rule ports, rules are created for IP addresses. The syntax is identical to the previous paragraph:
sudo ufw
Action – takes the Allow or Deny value, IP address – the address of the equipment that is granted / denied access to the server.
For example, the command to allow a device with an IP address of 10.68.23.15 to access all server ports can be written as follows:
sudo ufw allow from 10.68.23.15
A port identification option is also available, for example:
sudo ufw allow from 10.68.23.15 to any port 22
Adding the phrase to any port (name) specifies the specific value of the port for which access will be granted. Instead of name, specify the port number.
If you want to create a rule for multiple IP addresses, use the modified syntax:
sudo ufw allow from 10.68.23.0/24
Network Interface Operations
When creating profiles, the names of network interfaces are also used. The syntax is given below:
sudo ufw in on to any port
sudo ufw
The action field, as in the previous sections, accepts the Allow and Deny states, and the name_interface option is responsible for the name of the network interface for which the rule is being created.
To view the list of active interfaces, enter the command in the terminal:
ifconfig -a
An additional option is also available to any port – to uniquely identify the port.
Deleting entries
To delete a previously created rule, use the delete key. In general, the command looks like this:
sudo ufw delete
Where number is the serial number of the entry in the UFW configuration table. To put down numerical values for each line, specify in the terminal:
sudo ufw status numbered
After that, simply indicate the record number in the table. Let’s say:
sudo ufw delete 7
No reboot required.
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