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Difficulty: MediumOSI Model Layers and Functions

A network administrator is reviewing the packet processing logic of an enterprise Ethernet switch. Which of the following functions and data structures operate strictly within Layer 2 (Data Link Layer) of the OSI model? (Select TWO.)

  1. Appending a Cyclic Redundancy Check (CRC) frame check sequence trailer for error detectionAnswer
  2. Evaluating destination Media Access Control (MAC) addresses to make frame forwarding decisionsAnswer
  3. C
    Encapsulating transport segments into logical IP datagrams containing source and destination addresses
  4. D
    Managing port numbers to multiplex multiple application data streams over a single network connection

Answer

The operations residing strictly at Layer 2 (Data Link Layer) are appending a Cyclic Redundancy Check (CRC) frame check sequence trailer for error detection and evaluating destination Media Access Control (MAC) addresses to make frame forwarding decisions.
Layer 2 (Data Link Layer) is responsible for node-to-node data transfer across a physical medium. It encapsulates Layer 3 packets into frames, utilizes physical Media Access Control (MAC) addresses for local delivery, and appends a Frame Check Sequence (FCS) containing a Cyclic Redundancy Check (CRC) to detect transmission errors.

Step-by-Step Solution

1
Analyze each network function to determine its respective OSI layer.
CRC error detection and MAC address processing belong to Layer 2 (Data Link). Logical IP addressing belongs to Layer 3 (Network). Port multiplexing belongs to Layer 4 (Transport).
Layer 2 handles node-to-node framing, hardware addressing (MAC), and error detection across a single physical link.
2
Select the choices corresponding to Layer 2 operations.
CRC frame check sequence generation and MAC-based switching are identified as the correct Layer 2 functions.
These two processes govern physical address navigation and frame integrity before data is passed up to Layer 3.

Key Concept

OSI Layer 2 (Data Link Layer) functions and protocol data unit (PDU) characteristics
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Topics

OSI Model Layers and Functions

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