Ports are the windows and doors of the cyberworld. Although there are other listening protocols (ICMP, IGMP, etc.), listening ports come in basically two major flavors: TCP and UDP. The following ports list is by no means a complete one. In addition, some of the applications we present here may be configured to use entirely different ports to listen on (for example, running a web server on port 12345 instead of port 80 or 443). However, this list gives you a good start in finding the holes that an attacker will exploit given the first chance he or she can get. For a more comprehensive listing of ports, see iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml or nmap.org/data/nmap-services.