iptables
List all Rules
iptables -n -v -L
Whitelist by Source IP
iptables -A INPUT -s 127.0.0.1 -p tcp -j ACCEPT
Allow SSH
iptables -A INPUT -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW,RELATED,ESTABLISHED -j ACCEPT
Set Chain Policy
iptables -P [INPUT | OUTPUT | FORWARD] [ACCEPT | DROP]
Specify Interface (e.g. Loopback)
iptables -A INPUT -i lo -j ACCEPT # incoming
iptables -A OUTPUT -o lo -j ACCEPT # outgoing
Load iptables Rules from File
iptables-restore /etc/iptables/rules.v4