Hello ,
I am traying to secure my firewall and i found this scan but i did not understand what does it mean :
iptables -t filter -N ??
and also what he rule of -j RETURN

# SYN-FLOODING
iptables -t filter -N syn-flood
iptables -t filter -A INPUT -i eth0 -p tcp --syn -j syn-flood
iptables -t filter -A syn-flood -m limit --limit 1/sec --limit-burst 4 -j RETURN
iptables -t filter -A syn-flood '-j LOG \--log-prefix "IPTABLES SYN-FLOOD:"'
iptables -t filter -A syn-flood -j DROP


and also when i add this lines i had a lot of problems (performance , blocking access to the others servers ... )

thanks

Cheat a new chain

If packets are 1 a second or no more then 4 a second return to the original jump point else do the following

What is the rule that jumps to this new chain? Sounds like it was working. But unless you show your rules I cannot tell you where you could improve them.