ufw

Verify Status

sudo ufw status
#output
Status: inactive
--OR--
Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing), deny (routed)
New profiles: skip

Enable the FW

sudo ufw enable
#output
Firewall is active and enabled on system startup

Disable the FW

sudo ufw disable

See FW Rules

sudo ufw status
#output
Status: active

To                         Action      From
--                         ------      ----
Anywhere                   DENY        10.10.10.10  

Change the Default Policy

sudo ufw default deny outgoing
sudo ufw default deny incoming

View ufw App List

sudo ufw app list | grep Nginx
#output
Nginx Full
Nginx HTTP
Nginx HTTPS

Block an IP Address/Subnet

sudo ufw deny from 10.10.10.10
sudo ufw deny from 10.10.10.10/24

Block Incoming Connections to a Network Interface

sudo ufw deny in on eth0 from 10.10.10.10

Allow Incoming Connections to a Network Interface

sudo ufw allow in on eth0 from 10.10.10.10

Allow an IP in

sudo ufw allow from 10.10.10.10

Deleting Rules

sudo ufw status numbered
#output
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] Anywhere                   DENY IN     10.10.10.10             
[ 2] Anywhere on eth0           ALLOW IN    10.10.10.11 

#now delete the rule
sudo ufw delete 1    

Allow by Application

sudo ufw allow “OpenSSH”
#output
Rule added
Rule added (v6)

Disable by Application

#get status 
sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
OpenSSH                    ALLOW       Anywhere                               
Nginx Full                 ALLOW       Anywhere                  
OpenSSH (v6)               ALLOW       Anywhere (v6)                   
Nginx Full (v6)            ALLOW       Anywhere (v6) 
#remove the service you want to deny 
sudo ufw allow "Nginx HTTPS"
--OR--
sudo ufw delete allow "Nginx Full"

Credit and Further Reading

https://www.digitalocean.com/community/tutorials/ufw-essentials-common-firewall-rules-and-commands