iptables

Save current rules

iptables-save >/etc/iptables/rules.v4

Note: requires package iptables-persistent

And keep it persistent at reboot, /etc/network/if-pre-up.d/iptables:

#!/bin/sh
/sbin/iptables-restore </etc/iptables/rules.v4

chmod +x /etc/network/if-pre-up.d/iptables

List rules

iptables -L

Flush everything

iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

source