This document provides a lesson on Ethernet and LAN switching using Wireshark, focusing on understanding the Ethernet frame structure and resolving Ethernet problems. Key topics include the details of Ethernet frames, errors to look for such as checksum errors, and other LAN-related issues. The lesson aims to equip participants with the knowledge to analyze network captures effectively.

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Network analysis Using Wireshark
Lesson 9:
Ethernet and LAN Switching

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• By the end of this lesson, the participant will be able to:
▫ Understand Ethernet frame structure
▫ Use Wireshark for resolving Ethernet problems
Lesson Objectives

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Ethernet frame structure
What problems to look for
Chapter Content

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The Ethernet Frame
Destination
MAC
Source
MAC
Protocol
Type
802.1q Data FCS
6 bytes 6 bytes 2 bytes 2 bytes 46–1,500 bytes 4 bytes
Priority CFI VLAN ID
Tag protocol
identifier
Tag control field
Proprietary
2-byte number
16 bits 3 bits 1 bit 12 bits
Protocol
Type
2 bytes
802.1Q
Tag
Tag ID: 8100 for 802.1Q
8a88 for 802.1ad
Priority: 8 levels, 0-7
CFI: Always set to “0”
VLAN ID: 0 – No VLAN
1 – Native VLAN
2-4096 Std. VLANs

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Frame Information
Frame
details

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Ethernet Information
Source
Address
Destination
Address

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Ethernet frame structure
What problems to look for
Chapter Content

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Checksum Errors
Bad
checksum

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Broadcasts
10Mbps
~10µS’s between packets

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Summary
• In this lesson we talked about:
▫ The Ethernet Protocol and what to look for in a capture fule
▫ LAN and Ethernet problems that might happen in your network
Thanks for your time
Yoram Orzach
yoram@ndi-com.com

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