Which of the following best describes what a port number is used for in TCP and UDP?

A port number is fundamental in TCP (Transmission Control Protocol) and UDP (User Datagram Protocol), serving as an identifier that specifies which application or service will handle incoming data. It helps differentiate between different processes and services running on a single device, allowing the operating system to direct network traffic to the appropriate application.

When a data packet arrives at a device, the port number included in the packet header tells the operating system which application should process the data. For example, web traffic typically uses port 80 for HTTP or port 443 for HTTPS, indicating to the system that the designated web server application should manage that data.

The other options do not accurately reflect the role of port numbers. Hardware identification does not relate to port usage, and security aspects like encryption are handled at different layers in networking protocols. In addition, while routing packets involves determining the best path for data to travel across a network, that responsibility lies with IP addresses rather than port numbers.