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Difficulty: HardEncapsulation and De-encapsulation

A database server receives an incoming SQL query sent over an Ethernet network from a remote application server. Place the following processing and de-encapsulation steps in the correct sequential order from initial frame reception at the physical layer to final payload consumption by the database application daemon.

  1. 1The network interface card validates the Frame Check Sequence (FCS) trailer and strips the Data Link layer header containing the source and destination MAC addresses.
  2. 2The network stack evaluates the IP header to verify the destination IP address and TTL before stripping the Layer 3 encapsulation.
  3. 3The operating system inspects the TCP destination port and sequence numbers within the segment header.
  4. 4The transport layer reassembles segment payloads into a contiguous byte stream buffer for the application.
  5. 5The database engine reads and parses the raw SQL command string from the socket buffer.

Answer

The correct de-encapsulation sequence proceeds bottom-up through the protocol stack: Layer 2 frame verification and Ethernet header stripping, Layer 3 IP header verification and removal, Layer 4 TCP port inspection, Layer 4 stream reassembly, and finally Layer 7 application parsing.
De-encapsulation requires a host network stack to process inbound data from the bottom of the OSI model to the top. The physical hardware first receives the frame, validates the Frame Check Sequence (FCS), and removes the Layer 2 Ethernet header. The underlying IP packet is passed to Layer 3, where destination IP address validity and Time to Live (TTL) are checked before stripping the IP header. The remaining Layer 4 TCP segment's header is parsed to match the destination port to an active socket, and out-of-order segments are reassembled. Finally, the raw payload is presented to the Layer 7 database engine for SQL parsing.

Step-by-Step Solution

1
Process incoming physical signal at Layer 2
Network Interface Card checks FCS CRC, confirms MAC address match, and strips the Ethernet header/trailer.
Data Link layer headers envelope the packet on physical media and must be parsed first by network hardware.
2
Process network addressing at Layer 3
IP stack verifies destination IP, decrementing TTL, and removes the IP header.
Network layer protocol headers (IPv4/IPv6) enclose the transport segment and are stripped once host delivery is confirmed.
3
Inspect transport protocol metadata at Layer 4
OS inspects TCP flags, destination port number (e.g., port 3306 or 5432), and checksum.
Transport layer headers dictate socket mapping and segment order.
4
Reassemble TCP payload segments
Out-of-order or fragmented segments are ordered into a contiguous stream in the socket buffer.
TCP must present a reliable stream to the application layer prior to higher-level parsing.
5
Deliver payload to Layer 7 Application
Database process reads the plain SQL text payload from the socket buffer.
Application layer receives raw unencapsulated user payload after all lower-layer control headers have been stripped.

Key Concept

De-encapsulation order on receiving hosts
Estimated Time:2m 0s
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Topics

Encapsulation and De-encapsulation

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