Master Ubuntu’s UFW: Simple Commands to Enable, Configure, and Manage Firewall Rules

Wiki

UFW (Uncomplicated Firewall) is the default firewall component on Ubuntu, designed to simplify iptables configuration. It provides a friendly interface for creating IPv4/IPv6 firewall rules.

Enable and Disable

# ufw enable // enable firewall
# ufw disable // disable firewall
# ufw reset // reset firewall, removing all rules and disabling it

You can check the firewall status with:

# ufw status
// inactive
Status: inactive

// after enabling
Status: active
... // additional rule output

The default policy is to allow all traffic.

# ufw default allow|deny  // set default rule
allow : allow
deny : deny

Protocol Rules

Protocol rules define firewall behavior based on protocols.

ufw [delete] [insert NUM] allow|deny [in|out] [PORT[/PROTOCOL]] [comment COMMENT]

delete : delete the rule
insert : insert at position NUM
allow|deny : allow or deny the rule
in|out : direction of traffic
PORT : port number
protocol : e.g., tcp or udp
comment : comment

Example: add a rule allowing SSH (port 22, TCP) at position 2:

# ufw insert 2 allow in 22/tcp

Disable inbound SSH:

# ufw deny in 22

IP Rules

IP rules can include ports and protocols.

ufw [delete] [insert NUM] allow|deny [in|out [on INTERFACE]] [proto PROTOCOL] [from ADDRESS [port PORT]] [to ADDRESS [port PORT]] [comment COMMENT]

INTERFACE : network interface
from ADDRESS : source IP
to ADDRESS : destination IP
PORT : port number (source or destination)

Example: allow TCP port 22 from 192.168.0.2:

# ufw allow proto tcp from 192.168.0.2 port 22

Example: allow traffic from 192.168.0.2:80 to 192.168.0.2:8080:

# ufw allow from 192.168.0.2 port 80 to 192.168.0.2 port 8080

Delete Rules

Rules can be deleted by content or by number.

Method 1

Prepend delete to the original rule command.

# ufw allow 22/tcp // add SSH rule
# ufw delete allow 22/tcp // delete SSH rule

Method 2

Use ufw status numbered to view rule numbers, then delete by number.

# ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22                         ALLOW IN    Anywhere

Delete the first rule:

# ufw delete 1

Recommended Settings

# ufw enable
# ufw allow ssh
# ufw default deny
# ... you can add further custom rules

For deeper understanding, refer to the official documentation; UFW is a wrapper around iptables, which works on all Linux distributions.

Link: https://www.cnblogs.com/Johnson-lin/p/11261338.html