#!/bin/sh

### 1: Drop invalid packets 
#iptables -t mangle -A PREROUTING -m conntrack --ctstate INVALID -j DROP  

### 2: Drop TCP packets that are new and are not SYN ### 
#iptables -t mangle -A PREROUTING -p tcp ! --syn -m conntrack --ctstate NEW -j DROP 
 
### 3: Drop SYN packets with suspicious MSS value ### 
#iptables -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP  

### 4: Block packets with bogus TCP flags ### 
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,ACK FIN -j DROP
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,URG URG -j DROP
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,PSH PSH -j DROP
#iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL NONE -j DROP

### 5: Block spoofed packets ### 
#iptables -t mangle -A PREROUTING -s 224.0.0.0/3 -j DROP 
#iptables -t mangle -A PREROUTING -s 169.254.0.0/16 -j DROP 
#iptables -t mangle -A PREROUTING -s 172.16.0.0/12 -j DROP 
#iptables -t mangle -A PREROUTING -s 192.0.2.0/24 -j DROP 
#iptables -t mangle -A PREROUTING -s 192.168.0.0/16 -j DROP 
#iptables -t mangle -A PREROUTING -s 10.0.0.0/8 -j DROP 
#iptables -t mangle -A PREROUTING -s 0.0.0.0/8 -j DROP 
#iptables -t mangle -A PREROUTING -s 240.0.0.0/5 -j DROP 
#iptables -t mangle -A PREROUTING -s 127.0.0.0/8 ! -i lo -j DROP   

### 7: Drop fragments in all chains ### 
#iptables -t mangle -A PREROUTING -f -j DROP  

### 8: Limit connections per source IP ### 
iptables -A INPUT -p tcp -m connlimit --connlimit-above 111 -j REJECT --reject-with tcp-reset  

### 9: Limit RST packets ### 
iptables -A INPUT -p tcp --tcp-flags RST RST -m limit --limit 2/s --limit-burst 2 -j ACCEPT 
iptables -A INPUT -p tcp --tcp-flags RST RST -j DROP  


### 10: Limit new TCP connections per second per source IP ### 
iptables -A INPUT -p tcp -m conntrack --ctstate NEW -m limit --limit 60/s --limit-burst 20 -j ACCEPT 
iptables -A INPUT -p tcp -m conntrack --ctstate NEW -j DROP  

### 11:SYNPROXY
#iptables -t raw -A PREROUTING -p tcp -m tcp --syn -j CT --notrack 
#iptables -A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 
#iptables -A INPUT -m conntrack --ctstate INVALID -j DROP

### SSH brute-force protection ### 
#iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --set#iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 10 -j DROP