Make sure that firewall operates in stateful mode

Work task: Make sure that firewall operates in stateful mode using iptables

Workaround:

iptables -P INPUT DROP

iptables -P FORWARD DROP

iptables -P OUTPUT DROP

iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

Letakkan rule dibagian paling atas, karena iptables akan membaca rule secara berurutan, setelah rule-rule iptables diatas, selanjutnya tinggal allow service-service yang ingin digunakan, misalnya:

# Allow remote ssh and http access

iptables -A INPUT -p tcp --dport 22 -j ACCEPT # ssh

iptables -A INPUT -p tcp --dport 80 -j ACCEPT # http

# Allow DNS lookups to be initiated from this server

iptables -A OUTPUT -p udp --dport 53 -j ACCEPT # dns

iptables -A OUTPUT -p tcp --dport 53 -j ACCEPT # dns