Chapter 3: VLANs

• Although a Cisco switch can be configured to support two types of trunk ports, IEEE 802.1Q and ISL, today only 802.1Q is used. • 802.1Q: An IEEE 802.1Q trunk port supports simultaneou[r]

CCNA – Semester 3

Chapter 3: VLANs

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Objectives

• Explain the role of VLANs in a network

• Explain the role of trunking VLANs in a network

• Configure VLANs on the switches in a network topology

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Types of VLANs

• Today there is essentially one way of implementing VLANs -port-based VLANs A -port-based VLAN is associated with a port called an access VLAN

• However in the network there are a number of terms for VLANs Some terms define the type of network traffic they carry and others define a specific function a VLAN performs

VLAN Types:

• Data VLAN:

– Is a VLAN that is configured to carry only user-generated traffic

– A VLAN could carry voice-based traffic or traffic used to manage the switch, but this traffic would not be part of a data VLAN

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Types of VLANs

• Default VLAN:

– All switch ports become a member of the default VLAN after the initial boot up of the switch

– The default VLAN for Cisco switches is VLAN 1, you cannot rename it and you can not delete it

– Layer control traffic, such as CDP and spanning tree protocol traffic, will always be associated with VLAN -this cannot be changed

– It is a security best practice to change the default VLAN to a VLAN other than VLAN

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Types of VLANs

• Native VLAN:

– A native VLAN is assigned to an 802.1Q trunk port An 802.1Q trunk port supports traffic coming from many VLANs (tagged traffic) as well as traffic that does not come from a VLAN (untagged traffic) The 802.1Q trunk port places untagged traffic on the native VLAN

– Native VLANs are set out in the IEEE 802.1Q

specification to maintain backward compatibility with untagged traffic common to legacy LAN scenarios

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Types of VLANs

• Management VLAN

– A management VLAN is any VLAN you configure to access the management capabilities of a switch

– VLAN would serve as the management VLAN if you did not proactively define a unique VLAN to serve as the

management VLAN

– You assign the management VLAN an IP address and subnet mask A switch can be managed via HTTP,

Telnet, SSH, or SNMP

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Types of VLANs

• Voice VLANs

VoIP traffic requires:

– Assured bandwidth to ensure voice quality

– Transmission priority over other types of network traffic

– Ability to be routed around congested areas on the network

– Delay of less than 150 milliseconds (ms) across the network

A Cisco Phone is a Switch: contains an integrated three-port 10/100 switch:

– Port connects to the switch or other voice-over-IP (VoIP) device

– Port is an internal 10/100 interface that carries the IP phone traffic

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Types of VLANs

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Types of VLANs

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Network Traffic Types

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Network Traffic Types

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Network Traffic Types

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Network Traffic Types

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Switch Port Membership Modes

• Switch ports are Layer 2-only interfaces associated with a physical port

A port can be configured to support these VLAN types:

• Static VLAN - Ports on a switch are manually assigned to a

VLAN

• Dynamic VLAN - This mode is not widely used in production

networks and is not explored in this course However, it is useful to know what a dynamic VLAN is A dynamic port VLAN membership is configured using a special server

called a VLAN Membership Policy Server (VMPS), based on the source MAC address of the device connected to the port

• Voice VLAN - A port is configured to be in voice mode so

that it can support an IP phone attached to it Before you configure a voice VLAN on the port, you need to first

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Switch Port Membership Modes

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Controlling Broadcast Domains with VLANs

• Without VLANs: In normal operation, when a switch

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Controlling Broadcast Domains with VLANs

• With VLANs: the broadcast frame arrives at the only other

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Controlling Broadcast Domains with Switches and Routers

Intra-VLAN Communication

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Controlling Broadcast Domains with Switches and Routers

Inter-VLAN Communication

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Controlling Broadcast Domains with VLANs and Layer Forwarding

SVI: switch virtual interface

• SVI is a logical interface configured for a specific VLAN You need to configure an SVI for a VLAN if you want to route

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VLAN Trunks

• It is hard to describe VLANs without mentioning VLAN trunks

• A trunk is a point-to-point link between one or more Ethernet switch interfaces and another networking device, such as a router or a switch

• Ethernet trunks carry the traffic of multiple VLANs over a single link

• A VLAN trunk allows you to extend the VLANs across an

entire network Cisco supports IEEE 802.1Q for coordinating trunks on Fast Ethernet and Gigabit Ethernet interfaces

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VLAN Trunks

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VLAN Trunks

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VLAN Trunks

802.1Q Frame Tagging

• Switches are layer devices, use the Ethernet frame header information to forward packets The frame header does not contain information about which VLAN the frame should belong to

• When Ethernet frames are placed on a trunk they need

additional information about the VLANs they belong to This is accomplished by using the 802.1q encapsulation header This header adds a tag to the original Ethernet frame

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VLAN Trunks

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Trunking Modes

• Although a Cisco switch can be configured to support two types of trunk ports, IEEE 802.1Q and ISL, today only 802.1Q is used

• 802.1Q: An IEEE 802.1Q trunk port supports simultaneous tagged

and untagged traffic An 802.1Q trunk port is assigned a default PVID, and all untagged traffic travels on the port default PVID All untagged traffic and tagged traffic with a null VLAN ID are

assumed to belong to the port default PVID A packet with a VLAN ID equal to the outgoing port default PVID is sent untagged All

other traffic is sent with a VLAN tag

• ISL (Inter-Switch Link): In an ISL trunk port, all received packets

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Trunking Modes

DTP (Dynamic Trunking Protocol )

• A Cisco proprietary protocol

• DTP manages trunk negotiation only if the port on the other switch is configured in a trunk mode that supports DTP DTP supports both ISL and 802.1Q trunks

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Configuring VLANs &Trunks Overview

Use the following steps to configure and verify VLANs and trunks on a switch network:

1 Create the VLANs

2 Assign switch ports to VLANs statically

3 Verify VLAN configuration

4 Enable trunking on the inter-switch connections

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Configure a VLAN

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Configure a VLAN

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Configure a VLAN

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Managing VLANs

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Managing VLANs

• Delete VLANs:

– No vlan vlan-id

• You can delete vlan database:

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Configure a Trunk

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Configure a Trunk

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Common Problems witch Trunks

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Common Problem with VLAN configurations

VLAN and IP Subnets

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Summary

• VLANs separate broadcast domains on switches

• VLANs improve network performance, management, and security

• VLAN can be used for data, voice, network protocol and network management traffic

• There are different membership modes: Static, Dynamic, and Voice VLAN mode

• Routers or Layer switches are required for inter-VLAN communication

• Trunks allow multiple VLANs to traverse a single link to simplify intra-VLAN communication across multiple switches

• IEEE 802.1Q is the standard trunking protocol

• 802.1Q uses a process of frame tagging to keep VLAN traffic separate as it traverse the trunk link