Cisco 3 - LAN Perrine. J Page 110/20/2015 Chapter 8 VLAN VLAN: is a logical grouping grouped by: function department application VLAN configuration is

Cisco 3 - LAN

Perrine. J Page 104/20/23

Chapter 8

VLAN

VLAN:

• is a logical grouping

• grouped by:

• function

• department

• application

VLAN configuration is done by software.

Cisco 3 - LAN


Chapter 8

Typically in LAN configuration, users are grouped based on their location in relation to the HUB they are connected to.

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HUB

HUB

Cisco 3 - LAN


Chapter 8

VLAN implementations offered a port-mapping that establishes a broadcast domain between default group of devices.

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Switch

Switch

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Cisco 3 - LAN


Chapter 8

Traditionally, the role of a router is to provide

• firewall

• broadcast management

• route processing & distribution

Routers are used to properly communicate between different VLANs. Use the routers as your backbone to transmit information at high bandwidth among your VLAN switches.

Routers in VLAN topologies provide

• broadcast filtering

• security

• traffic flow management

Cisco 3 - LAN


Chapter 8

Properties of VLANs:

• VLANs work at layer 2 & 3 of OSI model

• Communications between VLANs is by layer 3 routing

• VLANs provide a method of controlling network broadcast

• Network administrator assigns users to VLAN

• VLANs can increase network security by defining which network nodes can communicate with each other

A VLAN is a broadcast domain that one or more switches create.

Cisco 3 - LAN


Chapter 8

VLAN implementations offered a port-mapping that establishes a broadcast domain between default group of devices.

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Switch

Switch


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1st floor

Broadcast domain

Broadcast domain

Broadcast domain

Cisco 3 - LAN


Chapter 8

VLAN Operation

Ports that are assigned to the same VLAN share broadcasts.

Ports that do not belong to that VLAN do not share these broadcast.

There are two (2) methods in which to create VLANs:

1. Static VLANs –

This method is also referred to a port-based membership. As a device is connected to the network, it automatically assumes the VLAN of that port

2. Dynamic VLANs –

Dynamic VLANs are created through the use of software packages such as CiscoWorks 2000. With a VLAN Management Policy Server (VMPS), you can assign switch ports to VLANs dynamically based on the source MAC address of the device that is connected to the port.

Cisco 3 - LAN


Chapter 8

Static VLAN

The default VLAN for every port in the switch is VLAN1, or the management VLAN.

The management VLAN cannot be deleted; however, additional VLANs can be created and ports can be reassigned to these alternate VLANs.

A router is used to switch between different VLANs. Hence, each VLAN should have a unique Layer 3 network or subnet address assigned.

Cisco 3 - LAN


Chapter 8

Advantages of VLANs:

• reduce administration costs related to solving problems associated with moves, additions & changes

• 20%-40% of the workforce physically moves each year

• one can move the node to a new location without changing its’ IP / subnet address by plugging the node into port for that VLAN

• controls broadcast activity

• provide workgroup & network security

• save money by keeping their HUBs and connecting them to switches i.e. don’t’ have to ‘throw away’ the HUBs.

The goal of the end-to-end VLANs, is to maintain the 80/20 traffic flow rule – 80% of the traffic on the local VLAN, and 20% on a remote VLAN.

Cisco 3 - LAN


Chapter 8

Broadcast:

Switches (not talking about VLANs here) create ‘smaller collision’ domains, but they do not create smaller broadcast domains. Hence use routers which don’t propagate broadcasts.

Though by setting up the different VLANs on a switch, one can control the broadcast messaging from one VLAN to another.

Security:

• restrict the number of users in a VLAN group

• prevent another user from joining without first receiving approval from the VLAN network administrator

• configure all unused ports to a default low-service VLAN

• adding access list in the router

Cisco 3 - LAN


Chapter 8

Using Hubs with VLANs

Each hub segment that is connected to a switch port can be assigned to only one VLAN.

All stations that share a hub segment become members of the same VLAN group.

Cisco 3 - LAN


Chapter 8

Port-based VLANs (static):

• nodes connected to ports in the same VLAN have same VLAN ID.

• users are assigned by port

MAC address-based VLANs (dynamic):

• VLAN Management Policy Server (VMPS)

• are ports on a switch that can automatically determine their VLAN assignments

Protocol-based VLANs (dynamic):

• are ports on a switch that can automatically determine their VLAN assignments

• functions are based on:

• logical addressing

• protocol type

VLAN Types

Cisco 3 - LAN


Chapter 8

VLAN Frame Identification

With multiswitch VLANs, the frame headers are encapsulated or modified to reflect a VLAN ID before the frame is sent onto the link between the switches.

Multiple trunking methodologies include:

• IEEE 802.1q

• ISL (Inter-Switch Link Protocol)

• 802.10

• LANE (LAN Emulation)

Cisco 3 - LAN


Chapter 8

The most common approach for logically grouping users into distinct VLAN:

• frame filtering

• filtering table is developed. Can be based on

• MAC

• protocol

• each frame is examined

• depending on the ‘filter table’ sends the frame out the designated port

• frame identification

• unique VLAN ID is assigned to each VLAN in the switch

• the tagged frame travels the backbone among switches

• when the frame exits the switch on non-backbone, the identifier is removed

• this technique is chosen by IEEE (IEEE 802.1q)

• gaining as the standard trunking mechanism

• function at layer 2

Cisco 3 - LAN


Chapter 8

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Switch

Switch

VLAN1 VLAN2VLAN3

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Backbone

VLAN2

Packet with VLANID, added by the switch

VLAN2

VLANID is removed by the switch before sending to the target host.

Cisco 3 - LAN


Chapter 8

Inter-Switch Link Protocol

ISL is a Cisco proprietary encapsulation protocol that interconnects multiple switches.

FDDI 802.10

Is a Cisco proprietary method of transporting VLAN information inside the standard IEEE 802.10 frame for Fiber Distributed Data Interface (FDDI).

Cisco 3 - LAN


Chapter 8

LAN Emulation (LANE)

LANE is a standard defined by the ATM Forum that gives two stations attached via ATM the same capabilities they normally have if they are LANs such as Ethernet or Token Ring.

The function of the LANE protocol is to emulate a LAN on top of ATM network.

That is, the LANE protocols make an ATM network look and behave like an Ethernet or Token Ring LAN.

Cisco 3 - LAN


Chapter 8

FACTS

VLAN makes up a switched network that is logically segmented by functions, project teams or applications, without regard to the physical location of users.

Each switch port can be assigned to a VLAN.

Ports assigned to the same VLAN share broadcasts.

So VLANs are used to create broadcast domains.

VLAN implementation methods used to assign a switch port to a VLAN:

• port-centric

• static

• dynamic

Cisco 3 - LAN


Chapter 8

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Only the devices on the same VLAN contend with collisions. Hence broadcast traffic within one VLAN is not transmitted outside the VLAN.

Cisco 3 - LAN


Chapter 8

NOTE: For configuring static VLANs on Cisco 29xx switches:

• max number of VLANs is switch dependent & is limited by the number of ports on the switch.

• VLAN1 is one of the factory-default VLANs

• VLAN1 is the default Ethernet VLAN

• Cisco Discovery Protocol (CDP) & VLAN Trunking Protocol (VTP) advertisements are sent on VLAN1.

• same encapsulation protocol, such as 802.1q or ISL, must be configured on all switch trunks that participate in the VLAN.

• commands for configuring VLANs vary by model number.

• the catalyst 29xx IP address is in the VLAN1 broadcast domain.

• switch must be in VTP server mode to create, add, or delete VLANs.

Cisco 3 - LAN


Chapter 8

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For non-VLAN configuration, switches makes ‘smaller collision’ domain. However, they do not make ‘smaller broadcast’ domains. A broadcast messages is sent to all the devices connected to the switch.

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Cisco 3 - LAN


Chapter 8

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Switch B

Switch A

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Use routers to reduce the broadcast of messages. A broadcast on Switch A is broadcast to all of its users, but is not broadcasted to Switch B (because the router won’t send it onto Switch B!)

Non-VLAN

Router

Cisco 3 - LAN


Chapter 8

Local Office

Toll Office Toll Office

Tandem Office

Trunk

Line

Local Office Class 5Toll Office Class 4Tandem Class 3

Local Loop

Demarc

Documents

Cisco 3 - LAN Perrine. J Page 110/20/2015 Chapter 8 VLAN VLAN: is a logical grouping grouped by: function department application VLAN configuration is