Nmap - Network Discovery Options

Normally you would send pings to discover active devices before scanning. However in many cases Firewalls are configured to block normal ping requests and responses. Various methods may be used to try and get past such Firewalls.

TCP +ICMP Ping

The default discovery method fires out ICMP Ping and TCP ACK packets and waits for active devices to respond. Default Port used is 80, which is often not filtered.

TCP Ping

Uses TCP ACK packets, on Port 80. Works on networks or hosts that filter out ICMP Ping packets.

ICMP Ping

Sends ICMP Echo Request packets.

Don’t Ping

Do not send Pings before scanning. Allows you to scan networks where the Firewall is set to block Ping Requests and Responses.