CCNA Networking · Quick Reference

Module 6 — Data Link Layer Cheat Sheet

CCNA Networking

In one line: Layer 2 — the Data Link layer sits between the Physical layer (cables, signals) and the Network layer (IP routing). Its job is to provide access to the physical media and get fr...

Key Ideas

1Data Link Layer Purpose. Layer 2 — the Data Link layer sits between the Physical layer (cables, signals) and the Network layer (IP routing). Its job is to provide access to the physical media ...

2Network Topologies. A physical topology describes the actual physical layout of the media and devices (where the cables go). A logical topology describes how data actually flows through t...

3CSMA/CD — Wired Ethernet. CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is the media access method used in half-duplex Ethernet — legacy hub-based networks. Although modern f...

4CSMA/CA — Wireless 802.11. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used in wireless (IEEE 802.11 Wi-Fi) networks. Unlike wired Ethernet, radio-based transmission make...

5Data Link Frame Structure. A Data Link frame wraps the Network layer packet with a header and a trailer. The header contains addressing and control information; the trailer contains error detect...

Code Examples

SW1# show interfaces FastEthernet 0/1
FastEthernet0/1 is up, line protocol is up (connected)
  ...
  Full-duplex, 100Mb/s, media type is 10/100BaseTX
  ! Full-duplex and 100 Mbps — properly auto-negotiated

SW1# show interfaces FastEthernet 0/2
FastE...