chap 6

• VLANs provide segmentation and organizational flexibility in a switched network

  
• VLANs group devices within a LAN to communicate as if each device was attached to the same cable
• VLANs allow an administrator to segment networks based on factors like function, project team, or application, without regard for the physical location of the user or device
• Devices within a VLAN act as if they are in their own independent network, even if they share a common infrastructure with other VLANs
• VLANs improve network performance by separating large broadcast domains into smaller ones
• VLANs reduce unnecessary traffic on the network and boost performance by dividing flat Layer 2 networks into multiple logical workgroups
• Benefits of using VLANs include security, cost reduction, better performance, reducing the size of broadcast domains, improved IT staff efficiency, and simpler project and application management
• Each VLAN in a switched network corresponds to an IP network, and VLAN design must consider a hierarchical network-addressing scheme
• Types of VLANs:

  • Data VLAN: configured to carry user-generated traffic
  • Default VLAN: all switch ports become part of the default VLAN after the initial boot up, with Cisco switches defaulting to VLAN 1
  • Native VLAN: assigned to an 802.1Q trunk port, supports untagged traffic, and is VLAN 1 by default
  • Management VLAN: configured to access the management capabilities of a switch, with VLAN 1 being the default management VLAN
• Voice VLANs are needed to support Voice over IP (VoIP) and require assured bandwidth, transmission priority, ability to be routed around congested areas, and low delay across the network
• A trunk is a point-to-point link between two network devices that carries more than one VLAN, extending VLANs across an entire network
• VLAN trunks allow all VLAN traffic to propagate between switches, enabling devices in the same VLAN but connected to different switches to communicate without the intervention of a router
• VLANs can be used to segment a network into different logical groups for security or performance reasons

  
• To configure a voice VLAN on a Cisco switch, the switch port supporting voice traffic is connected to the IP phone, CDP frames are sent to provide VLAN information, frames associated with VLAN 150 are forwarded, and voice traffic is prioritized

  
• Fields in an Ethernet 802.1Q frame include:

  • Type field (TPID) set to 0x8100
  • User priority field
  • Canonical Format Identifier (CFI)
  • VLAN ID field supporting up to 4096 VLAN IDs

  
• In a network with a native VLAN on an 802.1Q trunk, each switch has two VLANs configured (VLAN 1 and VLAN 2), with VLAN 1 as the native VLAN

  
• A phone connected to a switch is configured to tag voice traffic frames with VLAN 150, prioritize voice frames, and forward data frames for VLAN 20

  
• The output of a 'show vlan brief' command on a Cisco switch displays 5 configured VLANs, with VLAN 1 as the default VLAN and listed ports assigned to each VLAN

  
• In a network with three VLANs, each PC is connected to a different switch, and the switches are connected to each other with a trunk link allowing VLANs to communicate

  
• VLANs provide segmentation and organizational flexibility in a switched network, grouping devices within a LAN to communicate as if each device was attached to the same cable
• VLANs allow network segmentation based on factors like function, project team, or application, regardless of the physical location of the user or device
• Devices within a VLAN act as if they are in their own independent network, even if they share a common infrastructure with other VLANs
• VLANs improve network performance by separating large broadcast domains into smaller ones, reducing unnecessary traffic and boosting performance
• Benefits of VLANs include security by separating sensitive data, cost reduction, better performance, reduced broadcast domains, improved IT staff efficiency, and simpler project and application management
• A data VLAN carries user-generated traffic, while a native VLAN is untagged on a trunk and serves as a common identifier on opposite ends of a trunk link
• A management VLAN is configured to access the management capabilities of a switch, with VLAN 1 being the default management VLAN
• Voice VLANs are needed to support Voice over IP (VoIP) traffic, requiring assured bandwidth, transmission priority, and the ability to be routed around congested areas on the network
• A VLAN trunk extends VLANs across an entire network, allowing all VLAN traffic to propagate between switches without the need for a router
• A network diagram with three VLANs: three switches, six PCs, each PC connected to a different switch, switches connected with a trunk link allowing VLAN communication

  
• A trunk is a single physical link carrying multiple VLANs; a native VLAN is untagged on a trunk, used for untagged traffic

  
• Configuration of a Cisco IP phone to use VLAN tagging

  
• Table of Cisco switch IOS commands: global configuration mode, interface configuration mode, set port to access mode, assign port to a VLAN, return to privileged EXEC mode

  
• Output of 'show vlan brief' on a Cisco switch: 20 configured VLANs, default VLAN 1, ports assigned to one or more VLANs

  
• Catalyst 2960 Series switches are Layer 2 devices using Ethernet frame header info to forward packets, not having routing tables
• Tagging Ethernet frames for VLAN identification is done using IEEE 802.1Q header, adding VLAN info to frames on a trunk
• VLAN tag field details: Type (TPID value), User priority, Canonical Format Identifier (CFI), VLAN ID (VID)
• Some devices add a VLAN tag to native VLAN traffic; control traffic on native VLAN should not be tagged
• When a Cisco switch trunk port receives untagged frames, it forwards them to the native VLAN
• Voice VLAN is needed to support VoIP, with a separate VLAN for voice traffic and another for data traffic
• Different Cisco Catalyst switches support various numbers of VLANs, with normal range VLANs numbered 1 to 1,005