Ports and Protocols
Numbered endpoints (0 to 65535) that identify which service a packet is destined for.
Port numbers divide into three ranges defined by IANA: well-known ports (0 to 1023) are reserved for standard services and require elevated privileges to bind; registered ports (1024 to 49151) are assigned to vendor applications such as RDP on 3389 and MySQL on 3306; dynamic or ephemeral ports (49152 to 65535) are assigned temporarily by the OS for the client side of a connection. For the N10-009 exam, the critical distinction is transport protocol: some services use TCP (FTP control on 21, SMTP on 25, HTTP on 80), others use UDP (TFTP on 69, SNMP on 161), and DNS on 53 uses both. Confusing TCP with UDP for the same port number is a common distractor.
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