312-50V9 Question #366: Real Exam Question with Answer & Explanation

The correct answer is D: Transport layer port numbers and application layer headers. Port numbers used to identify specific services (e.g., HTTP on port 80, HTTPS on port 443) reside in the Transport layer (Layer 4) within TCP or UDP headers. To filter traffic at the application level - blocking specific applications or protocols regardless of port - the firewall

Question

In order to prevent particular ports and applications from getting packets into an organization, what does a firewall check?

Options

ANetwork layer headers and the session layer port numbers
BPresentation layer headers and the session layer port numbers
CApplication layer port numbers and the transport layer headers
DTransport layer port numbers and application layer headers

Explanation

Port numbers used to identify specific services (e.g., HTTP on port 80, HTTPS on port 443) reside in the Transport layer (Layer 4) within TCP or UDP headers. To filter traffic at the application level - blocking specific applications or protocols regardless of port - the firewall must also inspect Application layer (Layer 7) headers, which carry application-specific protocol data (e.g., HTTP method, FTP commands). This combination describes a stateful or next-generation firewall (NGFW). The other options are incorrect because session layer port numbers (A, B) is a misattribution - port numbers belong to the Transport layer, not the Session layer - and option C inverts the layers, placing port numbers at the application layer and headers at the transport layer.

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