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Zorluk: Çok zorEncapsulation and De-encapsulation

A web server receives an incoming Ethernet frame carrying an HTTPS request over TLS/TCP. Arrange the following de-encapsulation steps performed by the receiving host network stack in the correct chronological sequence from first (bottom of stack) to last (top of stack).

  1. 1The Network Interface Card (NIC) processes raw physical signals into bits, validates the Frame Check Sequence (FCS), and removes the Ethernet header and trailer to expose the IP packet PDU.
  2. 2The Network layer validates the destination IP address, verifies the IP header checksum, strips the IPv4 header, and passes the resulting TCP segment PDU to the Transport layer.
  3. 3The Transport layer processes the sequence numbers, evaluates the destination port, strips the TCP header, and passes the assembled stream payload to the session/presentation protocol.
  4. 4The TLS protocol layer receives the encrypted application data unit, verifies cryptographic integrity signatures, decrypts the payload, and presents unencrypted data to the web service.
  5. 5The web server daemon (e.g., NGINX/Apache) parses the HTTP GET request headers and URL parameters from the unencrypted data stream to render a response.

Cevap

The correct sequence of de-encapsulation is: 1) NIC validates FCS and strips Ethernet header/trailer (Layer 2 frame to Layer 3 packet); 2) Network layer verifies destination IP and strips IPv4 header (Layer 3 packet to Layer 4 segment); 3) Transport layer processes port numbers and strips TCP header (Layer 4 segment to upper-layer data); 4) TLS layer decrypts the encrypted payload (Layer 5/6 Presentation layer processing); 5) Web server process parses the HTTP request (Layer 7 Application layer).
De-encapsulation operates strictly bottom-up (Layer 2 frame → Layer 3 packet → Layer 4 segment → Layer 5/6 decrypted session → Layer 7 application data). At each step, a device inspects its specific layer control header, verifies checksums/integrity, strips the header/trailer, and uses higher-layer protocol indicators (EtherType, IP Protocol field, TCP Port) to pass the remaining PDU up to the next layer.

Adım Adım Çözüm

1
Identify Data Link Layer (Layer 2) de-encapsulation
Ethernet frame header and trailer (FCS) are stripped by the NIC upon integrity verification, leaving an IP packet.
De-encapsulation always starts at the lowest layer (Layer 1/2) when receiving signals off the physical wire.
2
Identify Network Layer (Layer 3) de-encapsulation
Destination IP address is checked and the IPv4 header is stripped, leaving a TCP segment.
Layer 3 processing evaluates IP headers and uses the Protocol field (TCP=6) to direct the packet payload to the correct Layer 4 protocol engine.
3
Identify Transport Layer (Layer 4) de-encapsulation
TCP destination port (e.g., 443) is evaluated, sequence numbers are reassembled, and the TCP header is stripped.
Layer 4 uses port numbers to multiplex data streams to specific application sockets.
4
Identify Presentation/Session Layer (Layer 5/6) security unwrapping
TLS cryptographic records are decrypted to reveal the raw HTTP request text.
Decryption must occur after Layer 4 TCP segment reassembly completes, but before the HTTP application daemon can interpret the request syntax.
5
Identify Application Layer (Layer 7) execution
The web server application reads the raw HTTP GET request.
The top of the OSI stack processes pure application payload free of all transport, network, framing headers, and encryption layers.

Anahtar Kavram

Inbound De-encapsulation Sequence and PDU Unwrapping
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Konular

Encapsulation and De-encapsulation

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