Mastering Linux Security and Hardening - Second Edition

Scan types

There are lots of different scanning options, each with its own purpose. The SYN packet scan that we're using here is considered a stealthy type of scan because it generates less network traffic and fewer system log entries than certain other types of scans. With this type of scan, Nmap sends a SYN packet to a port on the target machine, as if it were trying to create a TCP connection to that machine. If the target machine responds with a SYN/ACK packet, it means that the port is in an open state and is ready to create the TCP connection. If the target machine responds with an RST packet, it means that the port is in a closed state. If there's no response at all, it means that the port is filtered, blocked by a firewall. As a normal ...