There's an example of iptables rules on archlinux wiki:
# Generated by iptables-save v1.4.18 on Sun Mar 17 14:21:12 2013 *filter :INPUT DROP [0:0] :FORWARD DROP [0:0] :OUTPUT ACCEPT [0:0] :TCP - [0:0] :UDP - [0:0] -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A INPUT -i lo -j ACCEPT -A INPUT -m conntrack --ctstate INVALID -j DROP -A INPUT -p icmp -m icmp --icmp-type 8 -m conntrack --ctstate NEW -j ACCEPT -A INPUT -p udp -m conntrack --ctstate NEW -j UDP -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j TCP -A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable -A INPUT -p tcp -j REJECT --reject-with tcp-reset -A INPUT -j REJECT --reject-with icmp-proto-unreachable COMMIT # Completed on Sun Mar 17 14:21:12 2013
A few days ago my friend asked me why is there
REJECT in the last three rules. He told me that there should be
DROP instead, and he mentioned something about better security in case of
So, I have two questions:
What do the three rules do?
Does it make any difference when I put there
REJECT --reject-with? If yes, what is the difference?