Applied Network Security

ACK scan

Another tool that could be used to map out the firewall rules, determining which ports are filtered or unfiltered. If the port is open or close then a RST packet should be given as a response for that port meaning that's unfiltered, however if you get no reply or an ICMP error and that classify it as filtered:

>>> ans,unans = sr(IP(dst="www.google.com")/TCP(dport=[80],flags="A"))