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Difficulty: MediumEncapsulation and De-encapsulation

An administrator observes network traffic arriving at an enterprise server hosting a web application. Which TWO of the following statements accurately describe the actions performed during the de-encapsulation process as the incoming frame moves up the destination host's protocol stack?

  1. The Network Interface Card (NIC) verifies data integrity using the Frame Check Sequence (FCS) and strips the Layer 2 header and trailer.Answer
  2. B
    The Network layer inspects the destination MAC address to determine which transport protocol should receive the encapsulated payload.
  3. The Transport layer reads the destination port number in the TCP header to route the payload to the correct application socket.Answer
  4. D
    The Data Link layer strips the UDP header to extract the enclosed IP packet before forwarding it to the Network layer.

Answer

The Network Interface Card verifies data integrity using the Frame Check Sequence (FCS) and strips the Layer 2 header and trailer, and the Transport layer reads the destination port number in the TCP header to route the payload to the correct application socket.
During de-encapsulation on a destination host, processing proceeds bottom-up through the OSI model. At Layer 2 (Data Link), the hardware interface validates the frame using the Frame Check Sequence (FCS) in the trailer and removes the Ethernet header and trailer. At Layer 4 (Transport), the protocol stack parses the destination port in the TCP header to deliver the reassembled payload to the correct application process.

Step-by-Step Solution

1
Analyze Layer 2 processing at the receiving Network Interface Card (NIC).
The NIC receives the raw bits, checks the FCS in the trailer for errors, and upon verification, strips the Ethernet header and trailer to expose the IP packet.
De-encapsulation moves bottom-up; Layer 2 checks integrity and strips frame control fields before passing payload to Layer 3.
2
Analyze Layer 3 processing at the Network layer.
The IP header is inspected to verify destination IP address and Protocol field value, revealing TCP.
Layer 3 removes the IP header and passes the remaining segment to the Transport layer indicated by the Protocol field.
3
Analyze Layer 4 processing at the Transport layer.
The Transport layer inspects the TCP destination port to map data to the listening service.
Port numbers at Layer 4 identify specific software applications or sockets awaiting incoming data.

Key Concept

Host De-encapsulation Stack Traversal
Estimated Time:1m 30s
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Topics

Encapsulation and De-encapsulation

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