GSLC Question #429: Real Exam Question with Answer & Explanation

The correct answer is C. The transport layer port numbers and the application layer headers. Firewalls filter traffic by inspecting transport layer port numbers and application layer headers to block unauthorized ports and applications from entering the enterprise network.

Question

What does a firewall check to prevent certain ports and applications from getting the packets into an Enterprise?

Options

AThe network layer headers and the session layer port numbers
BThe presentation layer headers and the session layer port numbers
CThe transport layer port numbers and the application layer headers
DThe application layer port numbers and the transport layer headers

Explanation

Firewalls filter traffic by inspecting transport layer port numbers and application layer headers to block unauthorized ports and applications from entering the enterprise network.

Common mistakes.

A. Session layer (Layer 5) does not contain port numbers - ports are a transport layer concept, making this pairing technically incorrect for describing firewall filtering.
B. The presentation layer (Layer 6) handles data formatting and encryption/decryption and does not expose port numbers or application-policy constructs relevant to firewall filtering.
D. Port numbers belong to the transport layer (Layer 4), not the application layer; reversing this pairing misrepresents how the OSI model assigns these functions.

Concept tested. Firewall OSI layer packet filtering mechanism

Reference. https://www.cisco.com/c/en/us/products/security/firewalls/what-is-a-firewall.html

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