guardar regras do iptables e fazer o restore utilizando e não utilizando network-manager

adicionar uma regra:
iptables -t nat -A POSTROUTING -o enp10s0 -j MASQUERADE

gravar as regras para ficheiro:
iptables-save > /etc/iptables.up.rules

não utilizando o nm:

editar o ficheiro /etc/network/if-pre-up.d/iptables:
#!/bin/sh
/sbin/iptables-restore < /etc/iptables.up.rules

torná-lo executável:
chmod +x /etc/network/if-pre-up.d/iptables

utilizando o nm:
editar o ficheiro /etc/NetworkManager/dispatcher.d/pre-up.d/iptables:

#!/bin/sh

LOGFILE=/var/log/iptables.log

if [ "$1" = lo ]; then
echo "$0: ignoring $1 for \`$2'" >> $LOGFILE
exit 0
fi

case "$2" in
pre-up)
echo "$0: restoring iptables rules for $1" >> $LOGFILE
/sbin/iptables-restore /etc/iptables.up.rules >> $LOGFILE 2>&1
#/sbin/ip6tables-restore /etc/network/ip6tables.up.rules >> $LOGFILE 2>&1
;;
*)
echo "$0: nothing to do with $1 for \`$2'" >> $LOGFILE
;;
esac

exit 0

torná-lo executável:
chmod a+x /etc/NetworkManager/dispatcher.d/pre-up.d/iptables

https://wiki.debian.org/iptables
https://feeding.cloud.geek.nz/posts/using-iptables-with-network-manager/