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http://oceanpark.com/notes/firewall_example.html

# Preliminaries
# -------------
#
# To permit machines internal to the network to be able to
# send IP packets to the outside world, enable IP Forwarding:
#
# echo 1 > /proc/sys/net/ipv4/ip_forward
#
# Prevent SYN floods from consuming memory resources:
#
# echo 1 > /proc/sys/net/ipv4/tcp_syncookies
#
# I place the above echo commands into /etc/rc.d/rc.local
# so that they will be executed at boot time.
#

Code: Select all

#
# Configure default policies (-P), meaning default rule to apply if no
# more specific rule below is applicable.  These rules apply if a more specific rule below
# is not applicable.  Defaults are to DROP anything sent to firewall or internal
# network, permit anything going out.
#
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT

#
# Flush (-F) all specific rules
#
iptables -F INPUT
iptables -F FORWARD
iptables -F OUTPUT
iptables -F -t nat