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CCNA Semester 3

Chapter 08Chap

ter 08

VLAN TRUNKINGVLAN TRUNKINGPROTOCOLPROTOCOL

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Table of ContentTable of Content

1 VTP2 Inter-VLAN routing overview

3 VLAN troubleshooting

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3

VTPVTP

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VTP conceptsVTP concepts

The role of VTP is to maintain VLAN

configuration consistency across a commonnetwork administration domain.

VTP is a messaging protocol that uses Layer 2trunk frames to manage the addition,deletion, and renaming of VLANs on a singledomain.

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A messaging system that advertises VLAN configuration information

Maintains VLAN configuration consistency throughout a commonadministrative domain

Sends advertisements on trunk ports only

VTP Protocol FeaturesVTP Protocol Features

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Forwardsadvertisements

Synchronizes

Not saved inNVRAM

Creates VLANs Modifies VLANs

Deletes VLANs

Sends/forwardsadvertisements

Synchronizes

Saved in NVRAM

Creates VLANs

Modifies VLANs

Deletes VLANs Forwardsadvertisements

Does notsynchronize

Saved in NVRAM

VTP ModesVTP Modes

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VTP Operation

VTP advertisements are sent as multicast frames.

VTP servers and clients are synchronized to the latest revision number.

VTP advertisements are sent every 5 minutes or when there is a change.

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VTP Pruning

Increases available bandwidth by reducing unnecessary flooded traffic

Example: Station A sends broadcast, and broadcast is flooded only toward

any switch with ports assigned to the red VLAN

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Three types of VTP messagesThree types of VTP messages

Summary advertisements

Advertisement requests

Subset advertisements

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Summary advertisementsSummary advertisements

Summary Advertisement1 2 3 4

Version Code Followers MgmtD len

Management domain name (zero-padded to32bytes)

Configuration revision number

Updater identifyUpdate timestamp (12 bytes)

MD5 digest (16 bytes)

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Advertisement requestAdvertisement request

Advertisement Request

1 2 3 4

Version Code Rsvd MgmtD len


Start value

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Subset advertisementSubset advertisement

Subset Advertisement

1 2 3 4

Version Code Seq-Num MgmtD len


Configuration revision number

Vlan-info field 1

:

Vlan-info field N

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Vlan-info field N formatVlan-info field N format

Info length Status Vlan-typeVlan-name len

ISL VLAN-id MTU size802.10 index

Vlan-name (padded with 0s to multiples of 4bytes)

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VTP domain name

VTP mode (server/client/transparent)VTP server mode is the default

VTP pruning VTP password

VTP trap

Use caution when adding a new switch to an existing domain.Add a new switch in client mode to prevent the new switch from

propagating incorrect VLAN information.

Use the delete vtp command to reset the VTP revision number.

VTP Configuration GuidelinesVTP Configuration Guidelines

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VTP configurationVTP configuration

Switch# vlan database

Switch(vlan)# vtp v2-modeSwitch(vlan)# vtp domain cisco

Switch(vlan)# vtp client/server/transparent

Switch# show vtp status

Switch# show vtp counters

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Creating a VTP Domain

wg_sw_1900#configure terminalEnter configuration commands, one per line. End with CNTL/Zwg_sw_1900(config)#vtp transparentwg_sw_1900(config)#vtp domain switchlab

wg_sw_1900(config)#vtp [server | transparent | client] [domaindomain-name] [trap {enable | disable}] [passwordpassword][pruning {enable | disable}]

Catalyst 1900

Catalyst 2950

wg_sw_2950#vlan databasewg_sw_2950(vlan)#vtp [ server | client | transparent ]wg_sw_2950(vlan)#vtp domain domain-namewg_sw_2950(vlan)#vtp passwordpasswordwg_sw_2950(vlan)#vtp pruningwg_sw_2950(vlan)#snmp-server enable traps vtpwg_sw_2950(vlan)#exit

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VTP Configuration ExampleVTP Configuration Example

wg_sw_1900(config)#vtp transparentwg_sw_1900(config)#vtp domain switchlab pruning enablewg_sw_1900(config)#exitwg_sw_1900#show vtpVTP version: 1

Configuration revision: 4Maximum VLANs supported locally: 1005

Number of existing VLANs: 6 VTP domain name : switchlab VTP password : VTP operating mode : Transparent VTP pruning mode : EnabledVTP traps generation : EnabledConfiguration last modified by: 0.0.0.0 at 00-00-0000

00:00:00wg_sw_1900#config terminalwg_sw_1900(config)#interface f0/26wg_sw_1900(config-if)#trunk on desirablewg_sw_1900(config-if)#exitwg_sw_1900(config)#exitwg_sw_1900#show trunk A

DISL state: On, Trunking: On, Encapsulation type: ISL

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INTER-VLAN ROUTING OVERVIEWINTER-VLAN ROUTING OVERVIEW

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VLAN-to-VLAN OverviewVLAN-to-VLAN Overview

Network layer devices combine multiple

broadcast domains.

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Physical and logical interfacesPhysical and logical interfaces

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Configuring inter-VLAN routingConfiguring inter-VLAN routing

Router(config)# interface fastethernet

port-number. Subinterface-number

Router(config-if)#encapsulation dot1q/isl vlan-

numberRouter(config-if)#ip address x.x.x.x y.y.y.y

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Routing Between VLANs with ISL TrunksRouting Between VLANs with ISL Trunks

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Routing Between VLANs with 802.1Q TrunksRouting Between VLANs with 802.1Q Trunks

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TROUBLESHOOTING VLANTROUBLESHOOTING VLAN

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VLAN troubleshooting processVLAN troubleshooting process

LEDs

(or networkmanageme

nt

equivalent)

O.K ?

Switch

configuratio

n OK?

Physicallink

connection

OK?

Vlan

configuration OK?

L2 path

betweenswitchs

OK?

Fix any problem withswitch hardware

Fix any problem withconfiguration statements

Check with CDP, fixany cabling problems

Fix any switch trunking or

ISL configuration problem

Fix any VLAN, spanning tree or

intermediate router problems

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Preventing broadcast stormsPreventing broadcast storms

Setting threshold values to high or lowdiscards excessive broadcast, multicast, orunicast MAC traffic.

Minimize the STP processes occurring

between devices.

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Troubleshooting VLANsTroubleshooting VLANs

Show vlan Show spanning-tree

Show sw-vlan

Debug sw-vlan packet

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Scenario 1:Scenario 1: A trunk link cannot be established between aA trunk link cannot be established between a

switch and a routerswitch and a router

1. Make sure that the port is connected and notreceiving any physical-layer, alignment orframe-check-sequence (FCS) errors.

2. Verify that the duplex and speed are setproperly between the switch and the router.

3. Configure the physical router interface with

one subinterface for each VLAN that willroute traffic.

4. Confirm that the router is running an IOSrelease that supports trunking.

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Scenario 2:Scenario 2: VTP is not correctly propagating VLANVTP is not correctly propagating VLAN

configuration changesconfiguration changes

1. Make sure the switches are connectedthrough trunk links.

2. Make sure the VTP domain name is thesame on all switches that need tocommunicate with each other.

3. Check the VTP mode of the switch.

4. If using VTP passwords, the same passwordmust be configured on all switches in theVTP domain.

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Scenario 3:Scenario 3: Dropped packets and loopsDropped packets and loops

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SummarySummary

Definition of VLAN Trunking Protocol (VTP)

Configuring inter-VLAN routing usingsubinterfaces on a router port

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Q&AQ&A

Documents

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