Chabot College

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Chabot College

• ET 99.09 Cisco Semester 3
• Chapter 3 VLANs
• M. McGregor, Los Medanos College, Pittsburg, CA

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Introduction to VLANs
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What is a VLAN?
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Why create VLANs?
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Switches are the core of VLANs
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VLAN Switching and Filtering

• Each switch has the intelligence to make
  filtering and forwarding decisions by frame,
  based on VLAN metrics defined by network
  managers, and to communicate this information to
  other switches and routers within the network.

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Frame filtering and tagging

• The most common approaches for logically
  grouping users into distinct VLANs are
• frame filtering
• frame tagging

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Frame Filtering
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Tradeoffs with frame filtering

• Filter-based VLANs do not scale well because each
  frame has to be referenced to a lookup table.
• The IEEE 802 committee has adopted frame tagging
  as the standard because it is more scalable.

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IEEE 802 VLAN Standardization
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Frame Tagging
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VLAN Flexibility
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Problems with broadcasts
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Problems with broadcasts

• When no routers are placed between switches,
  broadcasts (Layer 2 transmissions) are sent to
  every switched port.
• This is commonly referred to as a flat network
  where there is one broadcast domain across the
  entire network

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VLANs can control broadcasts
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VLANs can provide security
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VLANs provide flexibility
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Where are the routers?

• Layer 3 communication, either embedded in the
  switch or provided externally, is an integral
  part of any high-performance switching
  architecture.

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What are hubs good for?
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Leveraging your investment
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Port-Centric VLANs
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Port-centric VLANs

• VLAN Membership by port maximizes forwarding
  performance because
• Users are assigned by port.
• VLANs are easily administered
• Maximizes security between VLANs
• Packets do not leak into other domains
• VLANs and membership are easily controlled across
  network

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Static VLANs
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Dynamic VLANs

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

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VLANs across backbones
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VLANs across backbones

• Fast Ethernet - ISL (Inter-Switch Link)
• FDDI - IEEE 802.10
• ATM - LAN Emulation (LANE)

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VTP - VLAN Trunk Protocol

• VTP Domain
• VTP Configuration revision number
• VLAN IDs (ISL)
• Emulated LAN names (ATM)
• 802.10 SAID values (FDDI)
• MTU
• Frame format
• VLAN configuration