Base policy :
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
Logging issues :
iptables -N LOG_DROP
iptables -A LOG_DROP -j LOG --log-prefix '[IPTABLES DROP] : '
iptables -A LOG_DROP -j DROP
iptables -A FORWARD -j LOG_DROP
iptables -A INPUT -j LOG_DROP
iptables -A OUTPUT -j LOG_DROP
For the lo Interface
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
For DNS :
iptables -A INPUT -i ppp0 --protocol udp --source-port 53 -j ACCEPT
iptables -A OUTPUT -o ppp0 --protocol udp --destination-port 53 -j ACCEPT
iptables -A INPUT -i ppp0 --protocol tcp --source-port 53 -j ACCEPT
iptables -A OUTPUT -o ppp0 --protocol tcp --destination-port 53 -j ACCEPT
To access web :
iptables -A INPUT -i ppp0 --protocol tcp --source-port 80 -m state --state ESTABLISHED -j LOG_ACCEPT
iptables -A OUTPUT -o ppp0 --protocol tcp --destination-port 80 -m state --state NEW,ESTABLISHED -j LOG_ACCEPT