Port scanners, such as nmap8 (see Appendix B for more information), first identify active hosts in the address range specified by the user using Transport Control Protocol/Internet Protocol (TCP/IP) Internet Control Message Protocol (ICMP) ECHO and ICMP ECHO_REPLY packets. Once active hosts have been identified, they are scanned for open TCP and User Datagram Protocol (UDP) ports 9 that will then identify the network services operating on that host. A number of scanners support different scanning methods that have different strengths and weaknesses that are usually explained in the scanner documentation (see Appendix D for more information). For.
