VLANs

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VLANs

• Semester 3, Chapter 3
• Linda Stacy

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Table of Contents

• Virtual LANs (VLANs)

Go There!

• Segmentation with Switching Architecture

Go There!

• VLAN Implementation

Go There!

• Benefits of VLANs

Go There!
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Virtual LANs(VLANs)
Table of Contents
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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

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Segmentation with Switching Architecture
Table of Contents
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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 number
• MAC address
• protocol being used
• application being used

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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?

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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

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Routers Role in a VLAN

• A router provides connection between different
  VLANs
• For 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.

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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.

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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

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VLAN Implementation
Table of Contents
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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.

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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 port
• VLANs are easy to admin.
• provides increased security
• packets do not leak into other domains

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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

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Dynamic VLANs

• Defined
• Switch ports can automatically determine a users
  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 move
• centralized notification of unauthorized user

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Benefits of VLANs
Table of Contents
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VLANs Make Changes Easier

• Traveling Users
• 20 to 40 of work force moves every year
• net admins biggest headache
• largest 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 VLAN
• router configuration remains intact

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VLANs Control Broadcasts

• Routers provide an effective firewall against
  broadcasts
• Adding VLANs can extend a routers firewall
  capabilities to the switch fabric
• The smaller the VLAN, the smaller the number of
  users that are effected by broadcasts

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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 VLAN
• preventing user access without authorization
• configuring all unused ports to the Disabled
  setting
• control access by
• addresses
• application types
• protocol types

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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.

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Table of Contents
End Slide Show