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Chapter 14
Configuring VLAN
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Chapter Objectives
At the end of this Chapter you will be able to:
Understand basic concept of VLAN
Configure VLAN
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VLAN Basics

Layer 2 switched networks are typically designed—as flat networks. With this
configuration, every broadcast packet transmitted is seen by every device on
the net- work regardless of whether the device needs to receive that data or
not.

By default, routers allow broadcasts to occur only within the originating
network, while switches forward broadcasts to all segments. it’s called a flat
network is because it’s one broadcast domain
Flat Network Structure
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
You can solve many of the problems associated with layer 2 switching with
VLAN i.e.

VLANs greatly enhance network security.

VLANs increase the number of broadcast domains
VLAN 1
Host A
VLAN 2
Host B
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VLAN Memberships
Static VLANs
In Static Membership each switch port is configured manually with a
VLAN Membership based upon which VLAN the host needed to be a
member of.
Dynamic VLANs
On the other hand, a dynamic VLAN determines a node’s VLAN
assignment automatically. Using intelligent management software,
you can base VLAN assignments on hardware (MAC) addresses
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Identifying VLANs
There are two different types of links in a switched environment.

Access Ports
An access port belongs to and carries the traffic of only one VLAN. Traffic
is both received and sent in native formats with no VLAN tagging
whatsoever

Trunk Ports
A trunk link is a 100- or 1000Mbps point-to-point link between two
switches, between a switch and router, or even between a switch and
server, and it carries the traffic of multiple VLANs—from 1 to 4,094 at a
time
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Access and Trunk Links in a switched network
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Frame Tagging

This frame identification method uniquely assigns a user-defined ID to
each frame. Sometimes people refer to it as a “VLAN ID” or even “color.”

Once the frame reaches an exit that’s determined by the forward/filter
table to be an access link matching the frame’s VLAN ID, the switch will
remove the VLAN identifier. This is so the destination device can receive
the frames without being required to understand their VLAN
identification.
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VLAN Identification Methods
It’s how switches identify which frames belong to which VLANs, and
there’s more than one trunking method.41.0

Inter-Switch Link (ISL)
Inter-Switch Link (ISL) is a way of explicitly tagging VLAN information onto
an Ethernet frame. This tagging information allows VLANs to be
multiplexed over a trunk link through an external encapsulation method
(ISL), which allows the switch to identify the VLAN membership of a frame
over the trunked link.
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
IEEE 802.1Q
Created by the IEEE as a standard method of frame tagging, IEEE 802.1Q
actually inserts a field into the frame to identify the VLAN. If you’re
trunking between a Cisco switched link and a different brand of switch,
you’ve got to use 802.1Q for the trunk to work.
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VLAN Trunking Protocol (VTP)

Cisco created this one too. The basic goals of VLAN Trunking Protocol
(VTP) are to manage all configured VLANs across a switched internetwork
and to maintain consistency throughout that network VTP allows you to
add, delete, and rename VLANs—information that is then propagated to
all other switches in the VTP domain.
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VTP Modes of Operation
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
Server
This is the default mode for all switches. The switch must be in server
mode to be able to create, add, and delete VLANs in a VTP domain.

Client
In client mode, switches receive information from VTP servers.

Transparent Switches
In transparent mode don’t participate in the VTP domain or share its VLAN
database, but they’ll still forward VTP advertisements through any
configured trunk links. They can create, modify, and delete VLANs
because they keep their own database.
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Configuring VLANs

S1#config t

S1(config)#vlan ?

WORD ISL VLAN IDs 1-4094

internal internal VLAN

S1(config)#vlan 2

S1(config-vlan)#name Sales

S1(config-vlan)#vlan 3

S1(config-vlan)#name Marketing

S1(config-vlan)#vlan 4

S1(config-vlan)#name Accounting
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Routing between VLANs
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Configuring Inter-VLAN Routing

By default, only hosts that are members of the same VLAN can
communicate. To change this and allow inter-VLAN communication, you
need a router or a layer 3 switch.

To support ISL or 802.1Q routing on a Fast Ethernet interface, the router’s
interface is divided into logical interfaces—one for each VLAN. These are
called sub interfaces. From a Fast Ethernet or Gigabit interface, you can
set the interface to trunk with the encapsulation command:
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
ISR#config t

ISR(config)#int f0/0.1

ISR(config-subif)#encapsulation ?

dot1Q IEEE 802.1Q Virtual LAN

ISR(config-subif)#encapsulation dot1Q ?

<1-4094> IEEE 802.1Q VLAN ID
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Configuring VTP

All Cisco switches are configured to be VTP servers by default. To
configure VTP, first you have to configure the domain name you want to
use.

S1#config t

S1#(config)#vtp mode server

Device mode already VTP SERVER.

S1(config)#vtp domain Lammle

Changing VTP domain name from null to Lammle

S1(config)#vtp password hcl

Setting device VLAN database password to hcl
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THANK YOU
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