iptables DROP policy

-A INPUT -p tcp -m tcp --dport 22 -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --sport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 22 -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp -m tcp --sport 22 -m state --state NEW,ESTABLISHED -j ACCEPT

iptables DROP policy

原文：https://www.cnblogs.com/eiguleo/p/11406696.html