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GSLC · Question #429

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

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.

Security Architecture & Engineering

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

How the community answered

(63 responses)
  • A
    5% (3)
  • B
    2% (1)
  • C
    90% (57)
  • D
    3% (2)

Why each option

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

AThe network layer headers and the session layer port numbers

Session layer (Layer 5) does not contain port numbers - ports are a transport layer concept, making this pairing technically incorrect for describing firewall filtering.

BThe presentation layer headers and the session layer port numbers

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.

CThe transport layer port numbers and the application layer headersCorrect

Transport layer (Layer 4) port numbers identify TCP/UDP services such as port 80 or 443, allowing the firewall to permit or deny traffic based on the service type. Application layer (Layer 7) headers enable deep packet inspection to identify and control specific applications beyond simple port matching. Together, these two layers provide the visibility firewalls need to enforce enterprise access control policies.

DThe application layer port numbers and the transport layer headers

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

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

Topics

#firewall#packet inspection#port filtering#OSI layers

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