$IPT -A INPUT -p TCP -i $INET_IFACE -j tcp_inbound
$IPT -A INPUT -p UDP -i $INET_IFACE -j udp_inbound
$IPT -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets
# Drop without logging broadcasts that get this far.
# Cuts down on log clutter.
# Comment this line if testing new rules that impact
# broadcast protocols.
$IPT -A INPUT -p ALL -d 255.255.255.255 -j DROP
# Log packets that still&nbsdn'''t match
$IPT -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
--log-prefix "INPUT packet died: "
###############################################################################
#
# FORWARD Chain
#
echo "Process FORWARD chain ..."
# Used if forwarding for a private network
###############################################################################
#
# OUTPUT Chain
#
echo "Process OUTPUT chain ..."
# Generally trust the firewall on output
# However, invalid icmp packets need to be dropped
# to prevent a possible exploit.
$IPT -A OUTPUT -m state -p icmp --state INVALID -j DROP
# Localhost
$IPT -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$IPT -A OUTPUT -p ALL -o $LO_IFACE -j ACCEPT
# To internet
$IPT -A OUTPUT -p ALL -o $INET_IFACE -j ACCEPT
# Log packets that still&nb;o''''t match
$IPT -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
--log-prefix "OUTPUT packet died: "
###############################################################################
#
# nat table
#
###############################################################################
# The nat table is where network address translation occurs if there
# is a private network. If the gateway is connected to the Internet
# with a static IP, snat is used. If the gateway has a dynamic address,
# masquerade must be used instead. There is more overhead associated
# with masquerade, so snat is better when it can be used.
# The nat table has a builtin chain, PREROUTING, for dnat and redirects.
# Another, POSTROUTING, handles snat and masquerade.
echo "Load rules for nat table ..."
###############################################################################
#
# PREROUTING chain
#
###############################################################################
#
# POSTROUTING chain
#
###############################################################################
#
# mangle table
#
###############################################################################
# The mangle table is used to alter packets. It can alter or mangle them in
# several ways. For the purposes of this generator, we only use its ability
# to alter the TTL in packets. However, it can be used to set netfilter
# mark values on specific packets. Those marks could then be used in another
# table like filter, to limit activities associated with a specific host, for
# instance. The TOS target can be used to set the Type of Service field in