Using Ubuntu UFW

UFW a firewall configuration tool available on Ubuntu.  UFW provides a user friendly way to create an IPv4 and IPv6 ip/port based firewall rules.

By default UFW is disabled, it can be enabled by running the following. Please ensure you have firewall rules in place to allow SSH before you enable it!

sudo ufw enable

Allow Port/Protocol 

sudo ufw allow <port>/<optional: protocol>

Example: To allow incoming tcp and udp packets on port 53

sudo ufw allow 53

Example: To allow incoming tcp packets on port 53

sudo ufw allow 53/tcp

Deny Port/Protocol

sudo ufw deny <port>/<optional: protocol>

Example: To deny incoming tcp and udp packets on port 53

sudo ufw deny 53

Example: To deny incoming tcp packets on port 53

sudo ufw deny 53/tcp

Show existing rules

To list the rules currently in place, run the following

sudo ufw status verbose

or if you prefer a numbered list

sudo ufw status numbered

Allow by specific port and IP Address

sudo ufw allow from <ip address> to <protocol> port <port number>

example: allow ip address 192.168.0.4 access to port 22 for all protocols

sudo ufw allow from 192.168.0.4 to any port 22

Deleting rules by line number

First you will need to list the rule by line number:

sudo ufw status numbered

Then you can delete the relevant rules

sudo ufw delete <rule number>

Example: to delete rule 5

sudo ufw delete 5

Reference

https://help.ubuntu.com/community/UFW