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#!/bin/sh
. /etc/functions.sh
export WAN=$(nvram get wan_ifname)
export LAN=$(nvram get lan_ifname)
## CLEAR TABLES
for T in filter nat mangle; do
iptables -t $T -F
iptables -t $T -X
done
iptables -N input_rule
iptables -N output_rule
iptables -N forwarding_rule
iptables -t nat -N prerouting_rule
iptables -t nat -N postrouting_rule
### Port forwarding
# iptables -t nat -A prerouting_rule -p tcp --dport 22 -j DNAT --to 192.168.1.2
# iptables -A forwarding_rule -p tcp --dport 22 -d 192.168.1.2 -j ACCEPT
### INPUT
### (connections with the router as destination)
# base case
iptables -P INPUT DROP
iptables -A INPUT -m state --state INVALID -j DROP
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# allow
iptables -A INPUT -i \! $WAN -j ACCEPT # allow from lan/wifi interfaces
iptables -A INPUT -p icmp -j ACCEPT # allow ICMP
iptables -A INPUT -p 47 -j ACCEPT # allow GRE
#
# insert accept rule or to jump to new accept-check table here
#
iptables -A INPUT -j input_rule
# reject (what to do with anything not allowed earlier)
iptables -A INPUT -p tcp --syn --tcp-option \! 2 -j DROP
iptables -A INPUT -p tcp -j REJECT --reject-with tcp-reset
iptables -A INPUT -j REJECT --reject-with icmp-port-unreachable
### OUTPUT
### (connections with the router as source)
# base case
iptables -P OUTPUT DROP
iptables -A OUTPUT -m state --state INVALID -j DROP
iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# allow
iptables -A OUTPUT -j ACCEPT #allow everything out
#
# insert accept rule or to jump to new accept-check table here
#
iptables -A OUTPUT -j output_rule
# reject (what to do with anything not allowed earlier)
iptables -A OUTPUT -p tcp -j REJECT --reject-with tcp-reset
iptables -A OUTPUT -j REJECT --reject-with icmp-port-unreachable
### FORWARDING
### (connections routed through the router)
# base case
iptables -P FORWARD DROP
iptables -A FORWARD -m state --state INVALID -j DROP
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
# allow
iptables -A FORWARD -i br0 -o br0 -j ACCEPT
iptables -A FORWARD -i $LAN -o $WAN -j ACCEPT
#
# insert accept rule or to jump to new accept-check table here
#
iptables -A FORWARD -j forwarding_rule
# reject (what to do with anything not allowed earlier)
# uses the default -P DROP
### MASQ
iptables -t nat -A PREROUTING -j prerouting_rule
iptables -t nat -A POSTROUTING -j postrouting_rule
iptables -t nat -A POSTROUTING -o $WAN -j MASQUERADE
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