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Difficulty: MediumEncapsulation and De-encapsulation

A network analyst is inspecting the de-encapsulation process on a server receiving traffic for a web application. Once the Network Interface Card (NIC) strips the Layer 2 Ethernet frame header and trailer, which layer's header is processed next by the network stack, and what Protocol Data Unit (PDU) is exposed?

  1. The Layer 3 IP header is evaluated next, exposing an IP packet.Answer
  2. B
    The Layer 4 TCP header is evaluated next, exposing a TCP segment.
  3. C
    The Layer 4 UDP header is evaluated next, exposing a UDP datagram.
  4. D
    The Layer 7 HTTP header is evaluated next, exposing application data.

Answer

The Layer 3 IP header is evaluated next, exposing an IP packet.
During inbound de-encapsulation, protocol headers are stripped in bottom-up order (Layer 2 → Layer 3 → Layer 4 → Layer 7). Once the Layer 2 Ethernet frame header and trailer are removed, the operating system processes the Layer 3 IP header and handles the enclosed IP packet.

Step-by-Step Solution

1
Identify the starting point in the de-encapsulation hierarchy
The Layer 2 Data Link frame header and trailer have been removed by the NIC hardware.
Inbound de-encapsulation processes traffic from the bottom of the OSI stack upward.
2
Determine the next layer in the OSI stack
The payload is delivered to Layer 3 (Network Layer).
Layer 3 directly encapsulates Layer 4 data and sits immediately above Layer 2.
3
Identify the protocol header and PDU exposed at Layer 3
The IP protocol header is evaluated, exposing the IP packet.
The network stack must inspect IP addressing and routing header fields before handing payload up to Layer 4 transport protocols.

Key Concept

OSI De-encapsulation Sequence and PDU Layers
Estimated Time:1m 0s
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Topics

Encapsulation and De-encapsulation

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