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Difficulty: MediumOSI Model Layers and Functions

A network administrator is configuring traffic control policies across multiple subnets in an enterprise network. Which of the following functions and operations occur specifically at Layer 3 (Network Layer) of the OSI model? (Select TWO.)

  1. Encapsulating segments into packets containing logical source and destination IP addressesAnswer
  2. B
    Performing Frame Check Sequence (FCS) CRC calculations to detect physical link transmission errors
  3. Determining optimal path selection using dynamic routing protocols and routing tablesAnswer
  4. D
    Multiplexing multiple application data streams using TCP and UDP port numbers

Answer

The correct functions operating at Layer 3 (Network Layer) are encapsulating upper-layer data into IP packets with logical addressing and determining optimal path selection using routing tables.
Layer 3 (Network Layer) is responsible for logical addressing (IP addresses), packet encapsulation, and path selection (routing) between different networks. Therefore, encapsulating segments into packets with IP addresses and determining path selection via routing tables are correct Layer 3 functions.

Step-by-Step Solution

1
Identify the primary responsibilities of Layer 3 (Network Layer) in the OSI reference model.
Layer 3 handles logical IP addressing, packet creation, and path selection (routing) across subnets.
Layer 3 enables end-to-end host communication across disparate network segments.
2
Evaluate each provided option against Layer 3 operational boundaries.
Packet encapsulation with IP addresses and routing path determination belong to Layer 3. FCS error checking belongs to Layer 2, while port-based multiplexing belongs to Layer 4.
Distinguishing protocol data units (PDUs) and header responsibilities across OSI layers ensures accurate protocol stack analysis.

Key Concept

OSI Model Layer 3 (Network Layer) Functions
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Topics

OSI Model Layers and Functions

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