chapter 08 - vlan and trunking

8/13/2019 Chapter 08 - VLAN and Trunking

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Chapter 8

VLAN & Trunking


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Objectives

Upon completion of this chapter, you will beable to perform the following tasks:

Configure a VLAN

Configure VLAN Trunking Protocol (VTP) Configure a switch for trunkingConfigure a router for trunkingRouting between Vlans

Verify VLAN connectivity


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VLAN introduction


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VLAN Overview

Segmentation

Flexibility

Security

A VLAN = A broadcast domain = Logical network (subnet)


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Benefits of VLANs

Easily move workstations on the LAN.Easily add workstations to the LAN.Easily change the LAN configuration.Easily control network traffic.Improve security.


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VLAN Operations

Each logical VLAN is like a separate physical bridge VLANs can span across multiple switches Trunks carries traffic for multiple VLANs Trunks use special encapsulation to distinguish

between different VLANs

Switch A

GreenVLAN

BlackVLAN

RedVLAN

GreenVLAN

BlackVLAN

RedVLAN

Switch B

Trunk

Fast Ethernet


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VLAN Membership Modes

VLAN5

Static VLAN Dynamic VLAN

MAC = 1111.1111.1111

Trunk

VMPS

1111.1111.1111 = vlan 10

VLAN10

Port e0/9Port e0/4


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VLAN CONFIGURATION


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Configuring Static VLANsCreate VLANs:

Switch# vlan databaseSwitch(vlan)# vlan < vlan_number> name Switch(vlan)# exit

Assign ports to VLANs:Switch(config)# interface fastethernet 0/9Switch(config-if)#switchport access vlan < vlan_number>

Deleting VLANs

Use the no form of the command .EX :

Create VLANs:Switch# vlan databaseSwitch(vlan)# vlan 2 name VlanBGD Switch(vlan)# exit

Assign ports to VLANs:Switch(config)# interface fastethernet 0/9Switch(config-if)#switchport access vlan 2

Deleting VLANs Use the no form of the command .


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Verifying and save VLANconfiguration

show vlan

copy running-config startup-configCopy running-config TFTP


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TRUNKING


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Trunking concept

VLAN1

VLAN2

VLAN1

VLAN2

VLAN1

VLAN2

VLAN1

VLAN2

VLAN1

VLAN2

VLAN1 and VLAN2

TRUNK

A trunk is a single communications line that carriesdata of multiple Vlans.


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VLANs and trunking

ISL802.1Q (dot1q)


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Frames Tagging

ISL802.1Q (dot1q)


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ISL Tagging

Not intrusive to clientstations, client does notsee the ISL headerEffective betweenswitches, routers andswitches, switches andservers with ISL networkinterface cards

ISL trunks enable VLANs across a backbone

VLAN Tag addedby incoming

port

VLAN Tagstripped by

forwarding port

Inter-SwitchLink carries

VLAN identifier


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ISL Encapsulation

ISL Header26 bytes Encapsulated Ethernet frame

CRC4 bytes

Frames encapsulated with ISL header and CRCSupport for many VLANs (1024)

VLAN field

BPDU bit

DA Type User SA LEN

VLAN

AAAA03

BPDU

HSA VLAN BPDUBPDU INDEX RES


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IEEE 802.1q

802.1q does not actually encapsulate the originalframe instead, it adds an extra 4-byte header to themiddle of the original Ethernet header.802.1q encapsulation forces a recalculation of theoriginal FCS field in the Ethernet trailer

Dest Src Len/Type Data FCS

Dest Src Type Tag Len/Type Data FCS

Priority VLAN ID


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ISL and 802.1q Compared

Both ISL and 802.1q provide trunking.

Both allow the use of a 12-bit-long VLAN ID field. So,either works fine and supports the same number ofVLANs.Both support a separate instance of spanning tree foreach VLAN.

The header used by each varies, and only ISL actuallyencapsulates the original frame.


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Trunking implementation

Switch# show port capabilities

Switch # configure terminalSwitch(config)# interface f0/1Switch(config-if)# Switchport mode trunk.Switch(config-if)# Switchport trunk encapsulation dot1q/islSwitch # Show trunk


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Inter-VLAN issues and solutions

Every Vlan is one subnetwork.When a host on one VLAN wants to communicate with ahost on another, a router must be involved. Networks with many VLANs must use VLAN trunking to

assign multiple VLANs to a single router interface.


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Dividing a Physical Interface intoSubinterfaces

Physical interfaces can be divided into multiplesubinterfaces.


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Physical and logical interfaces


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Configuring Router for Trunking

Router(config)#Interface fastethernet port-numberRouter(config-if)#no shutdownRouter(config-if)#exit

Router(config)# interface fastethernet port-number . Subinterface-number

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


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R1

SW1SW2

Vlan1 Vlan1 Vlan2 Vlan3Vlan3Vlan2

F0/0.10:192.168.1.254F0/0.12:192.168.2.254F0/0.13:192.168.3.254

.1.20 .2.20 .3.20 .1. 10 .2.10 .3.10

EX : Configuring Router for Trunking


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VTP


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VLAN Trunking Protocol (VTP)

A messaging system that advertises VLANconfiguration informationMaintains VLAN configuration consistencythroughout a common administrative domainVTP sends advertisements on trunk ports onlySupport mixed media trunks (Fast Ethernet,

FDDI, ATM)

1.new vlan added

3.Sync to the latest vlan information

2

VTP Domain ICND


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VTP Modes

Transparent

Forwardsadvertisements

Synchronize Not saved in

NVRAM

Create vlans Modify vlans Delete vlans Sends/forwardsadvertisements

Synchronize Saved in NVRAM

Create vlans Modify vlans Delete vlans Forwardsadvertisements

Does notsynchronize

Saved in NVRAM


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VTP advertisements are sent as multicast frames

VTP servers and clients synchronized to latest revisionnumber

VTP advertisement are sent every five minutes or whenthere is a change

How VTP Works

1.Add new VLAN2.Rev 3 --> Rev 4

Server

Client Client

4.Rev 3 --> Rev 45.Sync new vlan info

3 3

4.Rev 3 --> Rev 45.Sync new vlan info


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VTP Pruning Increases available bandwidth by reducing unnecessaryflooded traffic

Example: Station A sends broadcast, broadcast is onlyflooded toward any switch with ports assigned to the redVLAN

Switch 4

Switch 2

Switch 6 Switch 3 Switch 1

Port 2

Floodedtraffic is

pruned

RedVLAN

Port 1

Switch 5

A

B


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VLAN Configuration Guidelines

Maximum number of VLANs is switch-dependent

Catalyst 1900 supports 64 VLANs with a separatespanning tree per VLANVLAN1 is One of the factory default VLANsCDP and VTP advertisements are sent on VLAN1

Must be in VTP server or transparent mode tocreate, add, or delete VLANs

VLAN Config ration Steps


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VLAN Configuration Steps

Enable VTP (optional)

Enable trunking

Create VLANs

Assign VLAN to ports


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VTP domain name

VTP mode (server/client/transparent)

VTP server mode is the default

VTP pruning

VTP password

VTP Configuration Guidelines

Use caution when adding a new switch into an existing domain. Anew switch should be added in client mode to prevent the newswitch from propagating incorrect VLANs information

Use the delete vtp command to reset the VTP revision number

wg_sw_2950#vlan database wg_sw_2950(vlan)#vtp [ server | client | transparent ] wg_sw_2950(vlan)#vtp domain domain-name wg_sw_2950(vlan)#vtp password password wg_sw_2950(vlan)#vtp pruning wg_sw_2950(vlan)#exit


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Verifying VTP Configurations

wg_sw_a#show vtpVTP version: 1Configuration revision: 4Maximum VLANs supported locally: 1005Number of existing VLANs: 6VTP domain name : switchlabVTP password :

VTP operating mode : TransparentVTP pruning mode : EnabledVTP traps generation : EnabledConfiguration last modified by: 10.1.1.40 at 00-00-0000 00:00:00

wg_sw_a#show vtp

chapter 08 - vlan and trunking

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