Network tools guide
Port Number
Port numbers help network protocols deliver data to the right service or application on a device. This page explains ports; it does not check whether any port is open.
How port numbers work
TCP and UDP use separate port-number spaces, with values from 0 through 65535. A connection is associated with a protocol, network address, and port so data can reach the intended service. Ports do not by themselves indicate that a service is available or secure.
Common examples
HTTPS commonly uses TCP port 443, and HTTP commonly uses TCP port 80. A service can be configured to use a different port, and firewalls or network policies may restrict access.