iptables rules

##Good rules to help you mitigate Layer protection, by ShieldCommunity community
#Please remember to ask us for other if you use panels (https://discord.gg/HhFxScZWAT) or xIsm4#9127

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

#2 > Packets that are not SYN (Only new=
iptables -t mangle -A PREROUTING -p tcp ! --syn -m conntrack --ctstate NEW -j DROP

#3 > Block trash MSS Values (Good)
iptables -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP

#4 > Block Bogus Packets with 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 (NOT GOOD SOMETIMES!!) > Block most of subnets
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

6# > Drop ICMPv4 protocol ping (Not v6) - (Good for ping-spam)
iptables -t mangle -A PREROUTING -p icmp -j DROP
iptables -A INPUT -p tcp -m connlimit --connlimit-above 80 -j REJECT --reject-with tcp-reset

7# > Limit connections (If you're large network increase it)

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

8# > Limit TCP connections per/s
iptables -t mangle -A PREROUTING -f -j DROP

9# > Limit fragmentation UDP flood

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# > SYNPROXY RULES:

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

11# > Avoid port scanning (Forwarding exploit)

iptables -N port-scanning
iptables -A port-scanning -p tcp --tcp-flags SYN,ACK,FIN,RST RST -m limit --limit 1/s --limit-burst 2 -j RETURN
iptables -A port-scanning -j DROP

12# > Avoid Linux connections (OPTIONALL!!)
iptables -A INPUT -p tcp -m tcp --dport 25565 --tcp-option 8 --tcp-flags FIN,SYN,RST,ACK SYN -j REJECT --reject-with icmp-port-unreachable

##Just install iptables-persistant for RedHat/CentOS based systems