ufw

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sudo ufw deny from <ip_range> port <port>

firewalld

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sudo firewall-cmd --add-rich-rule='rule family="ipv4" source address="<ip_range>" port protocol="tcp" port="<port>" drop'

UFW access control

when using long range public wifi it matters to block every port from incoming connections.

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sudo ufw default deny
sudo ufw prepend reject in on <intetfece name>
sudo ufw restart

when configuration is done, remember to restart ufw and reconnect existing interfaces.

although remote clients are blocked, self-issued connections are not. so be sure to use another computer for testing ufw effectiveness before and after configuration.