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Data link layer

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

The data link layer is the network-model layer that provides delivery between adjacent nodes over a shared physical medium.

The Data Link Layer is Layer 2 of the five-layer TCP/IP model. It prepares data for transmission over a physical medium and provides hop-to-hop delivery between adjacent nodes. Ethernet and Wi-Fi operate at this layer as well as at the Physical Layer. section 4.3 section 4.3.1

Key points to remember:

  • Addresses each message to the next-hop device using a MAC address, rather than directly to the final host. section 4.3.1 section 4.4
  • Encapsulates a packet with a Layer 2 header and trailer, producing a frame; the trailer supports transmission error checking. section 4.3.2

PC1 sends data to SRV1

A message from PC1 to SRV1 makes three hops: PC1 to R1, R1 to R2, and R2 to SRV1. At each hop, Layer 2 addresses the frame to the next device’s MAC address. At the sending host, Layer 2 adds its header and trailer before the bits travel across the physical medium.

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes
Defines Layer 2 addressing, hops, frames, headers, and trailers, but defers detailed Ethernet switching behavior.
Examples
Uses a PC1-to-SRV1 route, three network hops, Ethernet framing, and five-step encapsulation and de-encapsulation diagrams.
What it assumes
Assumes basic network communication concepts while defining layers, hops, headers, trailers, frames, and encapsulation.
What you can do after
Evaluate network paths by distinguishing hop-to-hop MAC delivery from end-to-end IP delivery and identifying Layer 2 frames.
How it connects
Connects the TCP/IP model with Ethernet, Wi-Fi, MAC addresses, IP addresses, encapsulation, and the Physical and Network Layers.
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.