[IPTABLES,TCPDUMP] Add cheats for iptables and tcpdump

cheatsheets/iptables

@@ -0,0 +1,18 @@
+# Show hit for rules with auto refresh
+watch --interval 0 'iptables -nvL | grep -v "0     0"'
+
+# Show hit for rule with auto refresh and highlight any changes since the last refresh
+watch -d -n 2 iptables -nvL
+
+# Block the port 902 and we hide this port from nmap.
+iptables -A INPUT -i eth0 -p tcp --dport 902 -j REJECT --reject-with icmp-port-unreachable
+
+# Note, --reject-with accept:
+#	icmp-net-unreachable
+#	icmp-host-unreachable
+#	icmp-port-unreachable <- Hide a port to nmap
+#	icmp-proto-unreachable
+#	icmp-net-prohibited
+#	icmp-host-prohibited or
+#	icmp-admin-prohibited
+#	tcp-reset