This document discusses VLANs (virtual local area networks) and their implementation and security. It defines VLANs as virtual broadcast domains that provide isolation between networks and easy management. VLANs require a layer 3 device like a router to communicate between VLANs. The document covers VLAN configuration, trunking protocols, and common VLAN attacks like switch spoofing and double tagging.

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2- VLANs
2.1 VLAN Overview
2.2 Implementing VLANs and VLAN Security

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2.1 VLAN Overview

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WHATISVLAN?
• Virtual Local Area Network
• 1 VLAN = 1 broadcast domain
• Easy management
• Provides isolation (Different
VLANs can’t communicate
each other without a Layer-3
device)

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VLANCOMMUNICATION
• Fa0/1 and Fa0/2 can
communicate each other
• Fa0/3 and Fa0/4 can
communicate each other
• Fa0/1 can’t communicate with
Fa0/3 and Fa0/4

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VLANBENEFITS
• Easy management
• Easy troubleshooting
• Better performance
• Cost reduction (less routers)
• Security

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VLANTYPES
• Default VLAN
• Data VLAN
• Voice VLAN
• Management VLAN
• Native VLAN
• Reserved VLAN

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VOICEVLANOPERATION
Fa 0/16
VLAN 30
VLAN 10

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VLANTRUNKING
VLAN 100 & VLAN 200
• Switch port modes :
Acess or Trunk
• Access : Just one VLAN
• Trunk : Multiple VLANs

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VLANTAGGING
• Frames are tagged on
switches for VLAN
identification
• Tagging protocols :
ISL & 802.1Q

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2.2 Implementing VLANs and VLAN Security

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VLANRANGES

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VLANCONFIGURATION
• ‘no’ command is used for deleting commands (i.e. no vlan 100 )
3
Trunk configuration

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DYNAMICTRUNKINGPROTOCOL
• Trunk ports can be manually
configured or they can negotiate
and establish a trunk with a
connected peer via dynamic
trunking protocol (DTP)
• Manual configuration is
preferred

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DYNAMICTRUNKINGPROTOCOL(cont)

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VERIFYINGTRUNKOPERATION
Fa0/1 Fa0/1
SW1 SW2

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VERIFYINGTRUNKOPERATION

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COMMONVLANATTACKTYPES
• Switch Spoofing Attack :
 Default switchport : Dynamic
Auto
 Attacker acts as a switch and
forms a trunk so can get all
VLAN information

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COMMONVLANATTACKTYPES
• Double Tagging Attack :
 attacker changes the original
frame to add two VLAN tags
 An outer tag, which is of his
own VLAN and an inner
hidden tag of the victim's
VLAN
 Attacker's PC must belong to
the native VLAN of the trunk
link.