https://ru.wikibooks.org/wiki/Iptables
https://serverfault.com/questions/129086/how-to-start-stop-iptables-on-ubuntu
https://webhostinggeeks.com/howto/how-to-disable-iptables-on-ubuntu/
    sudo systemctl disable netfilter-persistent
https://www.shellhacks.com/disable-iptables-temporary-ubuntu-debian-centos/
    !!! via iptables-save

inst
https://askubuntu.com/questions/1052919/iptables-reload-restart-on-ubuntu-18-04
    sudo apt install iptables-persistent
    # netfilter-persistent will be also auto-installed
        /lib/systemd/system/netfilter-persistent.service

2021
https://habr.com/ru/companies/ruvds/articles/580648/
https://te.legra.ph/Nastrojka-iptables-v-Linux-11-25
https://www.cyberciti.biz/faq/howto-iptables-show-nat-rules/
SiteSupport - iptables from zero up ru of 39:12
    https://www.youtube.com/watch?v=Q0EC8kJlB64
https://upcloud.com/community/tutorials/configure-iptables-ubuntu/
2020
https://losst.ru/nastrojka-iptables-dlya-chajnikov
2016
https://developers.redhat.com/blog/2016/10/28/what-comes-after-iptables-its-successor-of-course-nftables#known_limitations
    iptables deprecation
https://www.tecmint.com/start-stop-disable-enable-firewalld-iptables-firewall/
2013
KumarSiwal - Fundamentals of iptables of 1:04:03
    https://www.youtube.com/watch?v=fQF2vEvqHgU
????
https://1cloud.ru/help/linux/nastrojka_linus-firewall_iptables

faq
https://help.ubuntu.com/community/IptablesHowTo

iptables:
sudo iptables -L
    list rules
sudo iptables -nL
    .. in number form