ufw commands for Firewall access

ufw commands: –

Ubuntu, like most Linux distributions, comes with a built-in firewall called iptables or ufw

The Linux kernel includes the Netfilter subsystem, which is used to manipulate or decide the fate of network traffic headed into or through your server. All modern Linux firewall solutions use this system for packet filtering.

The kernel’s packet filtering system would be of little use to administrators without a userspace interface to manage it. This is the purpose of iptables: When a packet reaches your server, it will be handed off to the Netfilter subsystem for acceptance, manipulation, or rejection based on the rules supplied to it from userspace via iptables. Thus, iptables is all you need to manage your firewall, if you’re familiar with it, but many frontends are available to simplify the task.

ufw commands:- ufw – Uncomplicated Firewall

The default firewall configuration tool for Ubuntu is ufw. Developed to ease iptables firewall configuration, ufw provides a user-friendly way to create an IPv4 or IPv6 host-based firewall.

ufw by default is initially disabled. From the ufw man page:

“ufw is not intended to provide complete firewall functionality via its command interface, but instead provides an easy way to add or remove simple rules. It is currently mainly used for host-based firewalls.”

Below is some examples for ubuntu commands and how to use ufw

First ufw needs to be enabled, From a terminal or SSH enter

sudo ufw enable

To open a port (SSH in this example):

sudo ufw allow 22

Rules can also be added using a numbered format:

sudo ufw insert 1 allow 80

Similarly, to close an opened port:

sudo ufw deny 22

To remove a rule, use delete followed by the rule:

sudo ufw delete deny 22

It is also possible to allow access from specific hosts or networks to a port. The following example allows SSH access from host 192.168.0.2 to any IP address on this host:

sudo ufw allow proto tcp from 192.146.0.1 to any port 22

Replace 192.146.0.1 with 192.146.0.0/24 to allow SSH access from the entire subnet.

Adding the –dry-run option to a ufw command will output the resulting rules, but not apply them. For example, the following is what would be applied if opening the HTTP port:

sudo ufw --dry-run allow http

*filter
:ufw-user-input - [0:0]
:ufw-user-output - [0:0]
:ufw-user-forward - [0:0]
:ufw-user-limit - [0:0]
:ufw-user-limit-accept - [0:0]
### RULES ###

### tuple ### allow tcp 80 0.0.0.0/0 any 0.0.0.0/0
-A ufw-user-input -p tcp --dport 80 -j ACCEPT

### END RULES ###
-A ufw-user-input -j RETURN
-A ufw-user-output -j RETURN
-A ufw-user-forward -j RETURN
-A ufw-user-limit -m limit --limit 3/minute -j LOG --log-prefix "[UFW LIMIT]: "
-A ufw-user-limit -j REJECT
-A ufw-user-limit-accept -j ACCEPT
COMMIT
Rules updated

ufw can be disabled by:

sudo ufw disable

To see the firewall status, enter:

sudo ufw status

And for more verbose status information use:

sudo ufw status verbose

To view the numbered format:

sudo ufw status numbered

Note

If the port you want to open or close is defined in /etc/services, you can use the port name instead of the number. In the above examples, replace 22 with ssh.

This is a quick introduction to using ufw. Please refer to the ufw man page for more information.

Testing Open Ports

After using any of the methods above to open a port in Linux, ensure that the process is successful. The following methods are simple ways to check the open ports on a system.

View the listening ports with the netstat command:

netstat -lntu

The above article will help you to know the basic commands to access firewall in ubuntu.

In order to Disabling direct SSH Root Login and Permitting through “su” user in Linux click here.