Examkin

Question

Difficulty: HardEncapsulation and De-encapsulation

A security log server receives an incoming transmission containing a syslog message sent from a remote network gateway. As the destination host network stack processes this data unit through de-encapsulation, which transformation occurs specifically at Layer 3 immediately before payload processing is handed off to Layer 4?

  1. The IPv4 header is inspected and stripped, converting the Layer 3 packet into a Layer 4 UDP datagram containing source and destination port parameters.Answer
  2. B
    The Ethernet frame header and Frame Check Sequence (FCS) trailer are validated and stripped, converting the raw bits into a Layer 3 packet.
  3. C
    The UDP header containing destination port 514 is inspected and stripped, delivering the unencapsulated log text payload directly to Layer 3 memory.
  4. D
    The TCP header and sequence flags are evaluated and removed to convert the segment stream into a datagram payload for Network layer routing.

Answer

The IPv4 header is inspected and stripped, converting the Layer 3 packet into a Layer 4 UDP datagram containing source and destination port parameters.
During inbound de-encapsulation on a receiving host, each layer inspects its corresponding control header, performs integrity and address checks, and strips its header before passing the encapsulated payload upward. At Layer 3 (Network Layer), the host inspects the IP header, verifies the IP destination address, and removes the IP header. The remaining payload is a Layer 4 PDU (a UDP datagram containing source and destination port numbers), which is passed to Layer 4 for transport processing.

Step-by-Step Solution

1
Identify the OSI layer processing boundary described in the scenario
The scenario focuses on the specific de-encapsulation step occurring at Layer 3 (Network Layer) moving toward Layer 4 (Transport Layer).
De-encapsulation unwraps data headers sequentially from Layer 1 up to Layer 7.
2
Determine the PDU state at Layer 3
Layer 3 receives an IP packet from Layer 2 after the Ethernet header and trailer have been removed.
The Data Link layer strips Layer 2 framing before passing the enclosed packet to the Network layer.
3
Analyze Layer 3 processing actions
Layer 3 validates fields in the IP header (such as destination IP and Protocol identifier 17 for UDP), strips the IP header, and forwards the resulting Layer 4 segment/datagram to the Transport layer.
Stripping the Layer 3 header reveals the Layer 4 PDU (UDP datagram).

Key Concept

De-encapsulation PDU Transformations across OSI Layers
Estimated Time:2m 0s
Rate this question

Topics

Encapsulation and De-encapsulation

More questions from this topic