Ubuntu comes packaged with a very easy to use firewall tool called UFW. This is literally meaning uncomplicated firewall for Ubuntu.

The UFW syntax is a short and sweet option compared to iptables.

Turn on and enable UFW with (UFW is disabled by default):

sudo ufw enable

Turn off UFW with:

sudo ufw disable

Check UFW status and current rules with:

sudo ufw status

Allowing and denying

The format for setting a firewall rule is

sudo ufw allow|deny port/protocol

With protocol being optional.

Allowing incoming UDP on port 81:

sudo ufw allow 81/udp

Allow incoming TCP and UDP on port 81:

sudo ufw allow 81

Denying TCP on port 400:

sudo ufw deny 400/tcp

Allowing from an ip:

sudo ufw allow from 111.222.3.44

Blocking connections from an ip:

sudo ufw deny from 111.22.333.4

Allow HTTP or HTTPS:

sudo ufw allow http
sudo ufw allow https

Allow SSH:

sudo ufw allow ssh

Deny or allow by service name:

sudo ufw deny servicename