UFW stands for Uncomplicated Firewall. It is a front end to the iptables packet filtering system which you can use as an alternative to using raw iptables. It does this by providing an abstraction of the lower-level details (policies, interfaces) from network security settings thereby simplifying a workflow around configuring and maintaining working solutions for system administrators as well developers.

● Application profiles: UFW ships a couple of pre-configured application profiles to cover popular applications and services like Apache or Bind.

● IPv6 support: UFW supports IPv4 and IPV protocol as well so you do not have to worry for compatibility with the latest network infrastructure.

● There is some specific traffic allowed, and also there is a default deny policy that will prevent all incoming traffic from the system.

● Debugging and auditing — UFW logs every packet that it denies in transparent mode, as well OpenDPI application layer filtering using the LOG target built into the kernel; logging of "deny" packets also includes source addresses via syslog.

It is important because UFW makes it very easy and quick for administrators to configure a firewall on their systems to protect against unwanted traffic as well as controlling user access. UFW can reduce the complexity and mitigate these risks by providing a simple command line syntax for managing firewall rules. UFW is one of the most used tools by system administrators and Linux users.

How can I use ufw to enable inbound SSH connections on Linux servers such as Ubuntu or Debian from a given IP address or subnet? On an Ubuntu or Debian server, how do I use ufw to open the SSH 22/TCP port?

The abbreviation for simple firewall is UFW. Goal ufw is to give the user an easy interface while administering a Linux firewall. This guide will teach you how to open an incoming SSH port or connection on an Ubuntu Linux 16.04/18.04/20.04/24.04 LTS or Debian Linux Server using UFW.

To use the ufw command to open an SSH port, the syntax is as follows:

OR

The following is how one can add a comment:

Enter the following if you are using SSH on TCP port 2323:

In this example, I'll set up my server to accept SSH connections only from IP addresses 172.16.3.100 and 172.16.4.0/24 subnets (CIDR):

sudo ufw allow from 172.16.3.100 to any port 22
sudo ufw allow from 172.16.4.0/24 to any port 22 proto tcp

Verify it:

Status: active
To					Action			From
--					------			----
22/tcp				ALLOW			172.16.4.0/24

Try using the grep or egerp commands for filtering if you have a lot of UFW rules. For example:

Although the syntax is the same as before, we will also be restricting the destination IP address:

Enter the following to accept incoming SSH connections from the IP address 121.14.2.1:

Allow, for example, 200.106.28.0/24 to 200.106.29.1 SSH server and TCP port 22:

This is the syntax:

Alternatively:

With the ufw, we can also specify the IP address of the target SSH server:

Now that we have permitted inbound SSH connections from the IP address 220.55.1.1/29, type:

In the last example, open and permit SSH port connections to 10.7.0.1 with a destination TCP port 22 from a certain IP subnet, 10.7.0.0/24.

Allow incoming SSH connections, but refuse connections from an IP address that has made at least six connection attempts in the previous 30 seconds. This is the syntax:

OR

This is the syntax:

Sample outputs:

Status: active

To								Action			From
--								------			----
22								ALLOW			Anywhere                  
72.14.190.12 443/tcp				ALLOW			Anywhere                  
72.14.190.12 80/tcp				ALLOW			Anywhere                  

if ufw was not enabled the output would be:

sudo ufw status

Status: inactive

Enter the following to activate UFW with the default rules, which include an open SSH port:

You discovered how to use ufw on an Ubuntu or Debian Linux server to open the SSH port. If you follow these rules you can effectively use UFW to safeguard your Linux system.