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Difficulty: MediumEncapsulation and De-encapsulation

During a packet capture analysis on a receiving web server, a network technician traces an incoming Ethernet frame carrying an HTTP request. As the server's network stack begins de-encapsulating the data, the Network Interface Card (NIC) verifies the Frame Check Sequence (FCS) and strips the Layer 2 Ethernet header and trailer. Which Protocol Data Unit (PDU) is immediately passed up to the Network layer (Layer 3) for further processing?

  1. PacketAnswer
  2. B
    Segment
  3. C
    Frame
  4. D
    Data Payload

Answer

The Protocol Data Unit passed to Layer 3 is the Packet.
During de-encapsulation on an incoming host, the network stack processes data from the bottom up. The Data Link layer (Layer 2) processes the Ethernet Frame, checks for transmission errors using the trailer's Frame Check Sequence (FCS), and strips the Ethernet header and trailer. The payload remaining is an IP Packet, which is handed directly to the Network layer (Layer 3) to examine source and destination IP addresses.

Step-by-Step Solution

1
Identify the initial receiving layer and PDU
The receiving host receives physical signals and reconstructs a Layer 2 Frame.
The Ethernet protocol operates at Layer 2 (Data Link layer).
2
Perform Layer 2 de-encapsulation
The Layer 2 Ethernet header and trailer (FCS) are inspected and removed.
De-encapsulation unwraps outer headers to expose the inner payload.
3
Determine the resulting PDU passed to Layer 3
The remaining inner payload is an IP Packet.
Layer 3 (Network layer) operates on Packets containing IP addressing information.

Key Concept

OSI De-encapsulation Sequence and Layer PDUs
Estimated Time:1m 0s
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Topics

Encapsulation and De-encapsulation

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