CCNA Networking · Quick Reference

Module 7 — Ethernet Switching Cheat Sheet

CCNA Networking

In one line: Ethernet (IEEE 802.3) is the dominant LAN technology — it handles the vast majority of all wired network traffic worldwide. The most common frame format is DIX Ethernet II (also...

Key Ideas

1Ethernet Encapsulation. Ethernet (IEEE 802.3) is the dominant LAN technology — it handles the vast majority of all wired network traffic worldwide. The most common frame format is DIX Etherne...

2MAC Address Format. A MAC address (Media Access Control address) is a 48-bit hardware identifier assigned to every network interface. It is used for Layer 2 addressing within a network se...

3Unicast, Broadcast, and Multicast MAC Addresses. Not all MAC addresses represent a single device. The type of MAC address in the destination field tells the switch — and the receiving devices — who the frame is inten...

4How Switches Learn and Forward. Switches operate at Layer 2 and maintain a MAC Address Table (also called the CAM table — Content Addressable Memory). This table maps MAC addresses to switch ports, a...

5Switch Forwarding Methods. How fast a switch starts forwarding a frame depends on which forwarding method it uses. There is a fundamental trade-off between latency (how fast) and reliability (er...

Code Examples

! MAC address notation formats (all represent the same address):
AA:BB:CC:DD:EE:FF  ! Linux/macOS colon-separated
AA-BB-CC-DD-EE-FF  ! Windows hyphen-separated
AABB.CCDD.EEFF     ! Cisco IOS dot-separated (groups of 4)

! View MAC address in Windows
C...

! Initially empty — switch just powered on
SW1# show mac address-table dynamic
! (no entries)

! PC1 (MAC: 0001.0001.0001) pings PC2 (MAC: 0002.0002.0002)
! Switch learns PC1's MAC from the INCOMING frame source MAC
SW1# show mac address-table dynamic...