iptables

https://interface31.livejournal.com/83089.html

https://interface31.ru/tech_it/2020/02/osnovy-iptables-dlya-nachinayushhih-chast-1.html

https://timeweb.cloud/tutorials/centos/kak-nastroit-iptables-na-centos

Stop ipfilters

https://serverfault.com/questions/129086/how-to-start-stop-iptables-on-ubuntu

https://www.cyberciti.biz/faq/ubuntu-server-disable-firewall/

Finally, type the following commands to stop firewall and flush all the rules:
$ sudo iptables -X
$ sudo iptables -t nat -F
$ sudo iptables -t nat -X
$ sudo iptables -t mangle -F
$ sudo iptables -t mangle -X
$ sudo iptables -P INPUT ACCEPT
$ sudo iptables -P FORWARD ACCEPT
$ sudo iptables -P OUTPUT ACCEPT