ISA/IEC 62443 Cybersecurity Fundamentals Specialist — Question 41

At Layer 4 of the Open Systems Interconnection (OSI) model, what identifies the application that will handle a packet inside a host?

Answer options

• A. A TCP/UDP application ID
• B. A TCP/UDP host ID
• C. A TCP/UDP port number
• D. A TCP/UDP registry number

Correct answer: C

Explanation

The correct answer is C, as TCP/UDP port numbers are used to distinguish different applications on a host that can receive packets. Options A and B refer to identifiers that do not specifically relate to application handling. Option D is incorrect because there is no such thing as a TCP/UDP registry number in this context.