Firewalld

Install on Ubuntu

apt install firewalld

Show status

firewall-cmd --state

Show open ports

firewall-cmd --list-ports

Show configuration

firewall-cmd --list-all

Allow a named service or a port

firewall-cmd --permanent --add-service=nfs3

OR

firewall-cmd --add-port=514/udp --permanent

Access from specific source ip (create a zone)

firewall-cmd --new-zone=mariadb-access --permanent
firewall-cmd --reload
firewall-cmd --get-zones
firewall-cmd --zone=mariadb-access --add-source=10.24.96.5/24 --permanent
firewall-cmd --zone=mariadb-access --add-port=3306/tcp  --permanent
firewall-cmd --reload

Port forwarding

# Enable masquerading
firewall-cmd --add-masquerade --permanent

# Port forward to same port on a different server (local:22 > 192.168.2.10:22)
firewall-cmd --add-forward-port=port=22:proto=tcp:toaddr=192.168.2.10 --permanent

# Port forward to different port on a different server (local:7071 > 10.50.142.37:9071)
firewall-cmd --add-forward-port=port=7071:proto=tcp:toport=9071:toaddr=10.50.142.37 --permanent