During host discovery, what does Nmap send to port 80?

During host discovery, what does Nmap send to port 80?

• A. TCP ACK
• B. SYN
• C. FIN
• D. RST

Answer: (A)

Host discovery uses lightweight probes to check if a host is reachable without opening a full connection. Nmap uses a TCP ACK probe to port 80 for this purpose. Sending an ACK without completing a handshake is less intrusive and helps determine reachability behind basic firewall rules. If the host is up and port 80 isn’t filtered, you’ll typically get a RST response, signaling the host is reachable even though the port is closed. If there’s filtering, there may be no response, which still indicates the host is up but protected. Using a SYN probe would start a full handshake and be more intrusive, while FIN or RST probes don’t reliably indicate reachability in this context. So, the TCP ACK probe to port 80 best serves host discovery.

Host discovery uses lightweight probes to check if a host is reachable without opening a full connection. Nmap uses a TCP ACK probe to port 80 for this purpose. Sending an ACK without completing a handshake is less intrusive and helps determine reachability behind basic firewall rules. If the host is up and port 80 isn’t filtered, you’ll typically get a RST response, signaling the host is reachable even though the port is closed. If there’s filtering, there may be no response, which still indicates the host is up but protected. Using a SYN probe would start a full handshake and be more intrusive, while FIN or RST probes don’t reliably indicate reachability in this context. So, the TCP ACK probe to port 80 best serves host discovery.