VLANs

Semester 3, Chapter 3Allan Johnson

Website: http://perdana.fsktm.um.edu.my/~rosli/WRES2108/index.htm

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Virtual LANs (VLANs)

Segmentation with Switching Architecture

VLAN Implementation

Benefits of VLANs

Go There!

Go There!

Go There!

Go There!

Virtual LANs(VLANs)

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Existing Shared LAN Configurations

In a typical shared LAN... Users are grouped physically based on the hub they are

plugged into Routers segment the LAN and provide broadcast firewalls

In VLANs... you can group users logically by function, department or

application in use configuration is done through proprietary software

Segmentation with Switching Architecture

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Grouping Users

VLANs can logically segment users into different subnets (broadcast domains)

Broadcast frames are only switched between ports on the switch or switches with the same VLAN ID.

Users can be logically group via software based on:port numberMAC addressprotocol being usedapplication being used

Differences between LANs & VLANs

VLANs... work at Layer 2 & 3 control network

broadcasts allow users to be

assigned by net admin. provide tighter network

security. How?

VLANs Across the Backbone

VLAN configuration needs to support backbone transport of data between interconnected routers and switches.

The backbone is the area used for inter-VLAN communication

The backbone should be high-speed links, typically 100Mbps or greater

Router’s Role in a VLAN

A router provides connection between different VLANsFor example, you have VLAN1 and VLAN2. Within the switch, users on separate VLANs cannot talk to

each other (benefit of a VLAN!) However, users on VLAN1 can email users on VLAN2 but

they need a router to do it.

How Frames are Used in a VLAN

Switches make filtering and forwarding decisions based on data in the frame.There are two techniques used. Frame Filtering--examines

particular information about each frame (MAC address or layer 3 protocol type)

Frame Tagging--places a unique identifier in the header of each frame as it is forwarded throughout the network backbone.

More on Frame Tagging

Frame Tagging... is specified by IEEE 802.1q which states

frame tagging is the preferred way to implement VLANs

uniquely assigns a VLAN ID to each frame before it is forwarded across the backbone.

is understood by switches prior to any broadcasts or transmission to other switches or routers

places a tag in the frame...thus, frame tagging. So what layer?

is removed by the switch after frame exits the backbone and before frame is forwarded to the end station

VLAN Implementation

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Ports, VLANs, and Broadcasts

Three methods for implementing VLANs Port-Centric Static Dynamic

Each switched port can be assigned to a VLAN. This... ensures ports that do not share the same VLAN do not

share broadcasts. ensures ports that do share the same VLAN will share

broadcasts.

Benefits of Port-Centric VLANs

All nodes in the same VLAN are attached to the same router interface.

(Note: curriculum says “switched port”)

Makes management easier because...Users are assigned by

router portVLANs are easy to admin.provides increased securitypackets do not “leak” into

other domains

3 Port-Centric VLANs

Static VLANs

Defined Static VLANs are when

ports on a switch are administratively assigned to a VLAN

Benefits can be assigned by port,

address, or protocol type secure, easy to configure

and monitor works well in networks

where moves are controlled

Dynamic VLANs

DefinedSwitch ports can automatically determine a

user’s VLAN assignment based on either/or: MAC logical address protocol type

When a station is initially connected to an unassigned port, the switch checks an entry in the table and dynamically configures the port with the right VLAN

Benefits less administration (more upfront) when users

are added or movecentralized notification of unauthorized user

Benefits of VLANs

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VLANs Make Changes Easier

Traveling Users 20% to 40% of work force moves every year

net admin’s biggest headachelargest expense in managing networks. Moves may require...

recabling readdressing and reconfiguration

VLANs provide a way to control these costs. As long as the user still belongs to the same VLAN...simply configure the new switch port to that VLANrouter configuration remains intact

VLANs Control Broadcasts

Routers provide an effective firewall against broadcasts

Adding VLANs can extend a router’s firewall capabilities to the “switch fabric”

The smaller the VLAN, the smaller the number of users that are effected by broadcasts

VLANs Improve Security

Shared LANs are easy to penetrate...simply plug into the shared hub.

VLANs increase security by ...restricting number of users in a VLANpreventing user access without authorizationconfiguring all unused ports to the “Disabled” settingcontrol access by

addresses application types protocol types

VLANs Save Money

Hub Replacement & Segmentation The ports on a non-intelligent

hub can only be assigned one VLAN.

Replacing hubs with switches is relatively cheap compared to the benefit gained.

In the graphic, replacing the core hub in an extended star topology with a VLAN capable switch effectively microsegments one shared LAN into six.

Required Labs for this Chapter

Spend your lab time completing three of the four labs in this Chapter Lab 3.3.4.1--Creating VLANs Lab 3.3.4.2--Switch Management VLANs Lab 3.4.4.2--Multi-Switch VLANs

Recommendation: DO NOT TAKE THE TEST UNTIL YOU’VE COMPLETED

THE LABS!!

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