Is there a firewall in my Shell?

Yes!

Your Shell works exactly like a regular server when it comes to security. You may use the firewall within the operating system to apply protection. 

• The default firewall configuration tool for Ubuntu is ufw. 

To enable a firewall in Ubuntu Shell, type the following in a terminal:

sudo ufw enable

Open ssh port (22 by default):

sudo ufw allow 22

Allow access from specific hosts or networks to a port:

sudo ufw allow proto tcp from *source ip* to *destination ip* port *port number*

Checking UFW Status and Rules:

sudo ufw status verbose