Linux Firewalls
UFW, IPTables, Firewalld

UFW
UFW (Uncomplicated Firewall) 
 UFW is just a front for IPTables. 
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 Check UFW status 
 ufw status 
 Enable UFW 
 ufw enable 
 Disable UFW 
 ufw disable 
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 UFW preset rule options 
 UFW may have preset rulesets that can be used for applications you have installed. 
 View available rule presets for installed apps: 
 ufw app list 
 View available preset protocol rules 
 less /etc/services 
 You'll see an output something like: 
 Available applications:

 Apache

 Apache Full

 Apache Secure

 Nginx Full

 Nginx HTTP

 Nginx HTTPS

 OpenSSH 
 You can then use the preset options to set rules 
 UFW allow option 
 ie 
 ufw allow nginx 
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 Port Rules 
 When adding port/IP rules, its best practice to add a comment to ensure the rule can be clearly identified. This is done using the comment function, as an example: ufw allow 80/tcp comment "web ports" 
 Basic port allow rule 
 ufw allow 80/tcp 
 Basic port deny rule 
 ufw deny 80/tcp 
 Multiple port allow rule 
 ufw allow 20,21/tcp 
 Multiple port block rule 
 ufw deny 20,21/tcp 
 Port range allow rule 
 ufw allow 40000:40100/tcp 
 Port range block rule 
 ufw deny 40000:40100/tcp 
 IP Rules 
   
 ufw all proto TCP from IP_IP_IP_IP to any port 
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 UFW Rule Ordering 
 UFW reads rules in order from top to bottom, with the earlier rules taking priority over subsequent rules. 
 View existing rules with rule numbers 
 ufw status numbered 
 Specify position in ruleset when adding rule 
 ufw insert 3 allow 80/tcp 
 The above command would add an allow rule for port 80 after rule before the existing number 3 rule. 
 Add rule to top of list 
 ufw prepend allow 80/tcp 
 add rule to bottom of list 
 ufw append allow 80/tcp 
 Delete a rule 
 ufw delete rulenumber 
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