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IPT=iptables
# policies
$IPT -P INPUT DROP
$IPT -P OUTPUT DROP
$IPT -P FORWARD DROP
# flush chains
$IPT -F INPUT
$IPT -F OUTPUT
$IPT -F FORWARD
# accept everything on loopback
$IPT -A INPUT   -i lo -j ACCEPT
$IPT -A OUTPUT  -o lo -j ACCEPT
# accept UDP
$IPT -A INPUT -p udp -j ACCEPT
$IPT -A OUTPUT -p udp -j ACCEPT

# accept ESTABLISHED,RELATED
$IPT -A INPUT  -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# accept new outgoing TCP
$IPT -A OUTPUT -p tcp -m state --state NEW --syn -j ACCEPT
# accept new outgoing DNS
#$IPT -A OUTPUT -p udp --dport 53 -m state --state NEW -j ACCEPT
# accept new outgoing IPMI
#$IPT -A OUTPUT -p udp --dport 623 -m state --state NEW -j ACCEPT
# accept tftp
#$IPT -A OUTPUT -p udp --dport 69 -m state --state NEW -j ACCEPT
#$IPT -A INPUT -p udp --dport 69 -m state --state NEW -j ACCEPT
# accept DHCP
#$IPT -A OUTPUT -p udp --sport 68 --dport 67 -j ACCEPT
#$IPT -A INPUT  -p udp --sport 67 --dport 68 -j ACCEPT
# accept SSH
iptables -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT
# accept ping
$IPT -A OUTPUT -p icmp --icmp-type 8 -j ACCEPT
$IPT -A INPUT  -p icmp --icmp-type 0 -j ACCEPT