You are performing a port scan on a subnet that has the ICMP protocol blocked. You discover 23 live systems and after doing a port scan on each of them; you notice that they all show port 21 in closed state. What would be the next logical step that you should perform?

A.
Perform a ping sweep to identify any additional systems that might be up

B.
Connect to open ports to discover applications

C.
Perform a SYN scan on port 21 to identify any additional systems that might be up

D.
Rescan every computer to verify the results

Explanation:
As ICMP is blocked you’ll have trouble determining which computers are up and running by using a ping sweep. As all the 23 computers that you had discovered earlier had port 21 closed, probably any additional, previously unknown, systems will also have port 21 closed. By running a SYN scan on port 21 over the target network you might get replies from additional systems.