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
+ iptables -A INPUT -p tcp --syn --tcp-option \! 2 -j DROP
#
# 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