Ubuntu Firewall UFW

sudo apt-get install UFW

sudo UFW enable

sudo ufw default deny

Booted the firewall, boot up and shut down all external access to the native, but the local access is normal outside.

3. Turn ON/off

sudo ufw allow|deny

sudo UFW allow SMTP allows all external IPs to access native 25/TCP (SMTP) ports

sudo ufw allow 22/tcp allows all external IP access to the native 22/tcp (SSH) port

sudo UFW allow 53 allows external access to 53 ports (TCP/UDP)

sudo ufw allow from 192.168.1.7 allows this IP access to all native ports

sudo UFW deny SMTP prevents external access to the SMTP service

sudo ufw delete allow SMTP to delete a rule established above

4. View firewall status

sudo UFW status

Turn firewall on/off (default setting is disable)

sudo ufw enable|disable

Ubuntu Firewall UFW