Applications find each other on a host using port numbers, 16-bit values (0 to 65535) carried in the TCP or UDP header. Well-known ports (0 to 1023) are assigned to common services, registered ports (1024 to 49151) to other applications, and dynamic or ephemeral ports (49152 to 65535) are borrowed by clients. A server listens on a known port and a client connects to it from a random high-numbered source port. The exam expects you to recognise the port and transport of each common protocol and whether it is secure. Firewall rules, packet captures, scan results and troubleshooting all depend on this knowledge, so it is worth memorising properly.
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