Think it through together · A little story
A building has a library and a cafeteria. Knowing the building’s location is not enough; you also need to know which service desk to visit.
Lay out the process
- IP addressFind the host interface
- Transport protocolTCP, UDP, or another protocol
- Port numberDistinguish communication endpoints
Port numbers help an operating system deliver transport-layer communication to the right endpoint or service.
An IP address is like the building’s street address; a port is like a service desk number. TCP and UDP each have their own port space, so when discussing a port, it is important to say which protocol is being used.
Common services use well-known ports, while clients also use temporary ports of their own.
Your turn to try
If you know a server’s IP address, does the system need no other information to distinguish all of its network services?
Have you thought it through? Open for an explanation
It still needs information such as the protocol, port, and connection state to deliver communication to the right endpoint.
Take away one discovery
Port numbers help an operating system deliver transport-layer communication to the right endpoint or service.
Try covering the diagram above and explaining each step to someone in your family. If one step is hard to explain, go back and look at that card again.