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Difficulty: MediumEncapsulation and De-encapsulation

An enterprise server receives an Ethernet frame containing an HTTP request destined for its running web service. Which of the following operations occur during the de-encapsulation process as the incoming data moves up the protocol stack at the receiving host? (Select TWO.)

  1. The Network Interface Card validates the Frame Check Sequence in the Ethernet trailer and strips the Data Link header and trailer before passing the payload up to Layer 3.Answer
  2. The operating system inspects the destination port number within the Transport layer header to direct the unencapsulated payload to the specific web service process.Answer
  3. C
    An intermediate Layer 2 switch strips the IP header from the frame to determine the appropriate egress switchport.
  4. D
    The host operating system converts the segment directly into a frame before handing it off to the Application layer.

Answer

The correct statements are that the Network Interface Card validates the Frame Check Sequence in the Ethernet trailer and strips the Data Link header and trailer before passing the payload to Layer 3, and that the operating system inspects the destination port number within the Transport layer header to direct the unencapsulated payload to the specific web service process.
When a host receives network traffic, de-encapsulation occurs from Layer 2 up to Layer 7. The NIC validates frame integrity via the FCS and removes the Layer 2 header and trailer to pass the IP packet up. Subsequently, at Layer 4, the operating system inspects the destination port number to deliver the unencapsulated application data to the appropriate process.

Step-by-Step Solution

1
Analyze Layer 2 de-encapsulation at the receiving host
The NIC receives the physical signal, validates the Frame Check Sequence (FCS) in the Ethernet trailer for errors, and strips the Ethernet header and trailer to reveal the IP packet.
De-encapsulation unwraps data from the bottom up, removing outer Layer 2 encapsulation boundaries first.
2
Analyze Layer 3 processing
The Network layer examines the IP header, verifies the destination IP address matches the receiving host, and strips the IP header to expose the Transport layer segment.
Layer 3 processing validates addressing and identifies the encapsulated upper-layer protocol.
3
Analyze Layer 4 processing and application handoff
The Transport layer evaluates the TCP header, identifies the destination port number, and hands the clean payload to the designated application layer process.
Port numbers at Layer 4 provide socket-level multiplexing to target specific services.

Key Concept

De-encapsulation sequence and layer-specific PDU handling at the receiving host
Estimated Time:1m 30s
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Topics

Encapsulation and De-encapsulation

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