CCIE RS – Written – L2 – Implement and Troubleshoot VLANs

CCIE RS – Written – L2 – Implement and Troubleshoot VLANs

VLAN – Virtual LAN

  • Administratively defined subset of switch ports that are in the same broadcast domain
  • Broadcast domain – devices that can receive broadcast sent by another device
  • Best Practice – 1 to 1 relationship between IP subnet and VLAN

Configuration

  • Vlan [id]
  • Under interface > switchport access vlan [id]
  • Modify VLAN operational state (L2 only)
    • Can be suspended globaly for entire VTP or to local switch
    • Vlan [id] > state suspend (global) | shutdown (local)

Access Ports

Belongs and carries traffic for only 1 VLAN 

Configuration

interface > switchport access vlan [#]


VLAN Database

  • Vlan 0 – Reserved, not available for use
  • Vlan 1 – Default vlan for all access ports
    • Cannot be deleted or pruned
  • Vlan 4095 – Reserved, not available for use

Switch#sh vlan

VLAN Name                             Status    Ports
—- ——————————– ——— ——————————-
1    default                          active    Gi0/0, Gi0/1, Gi0/2
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup 

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
—- —– ———- —– —— —— ——– —- ——– —— ——
1    enet  100001     1500  –      –      –        –    –        0      0   
1002 fddi  101002     1500  –      –      –        –    –        0      0   
1003 tr    101003     1500  –      –      –        –    –        0      0   
1004 fdnet 101004     1500  –      –      –        ieee –        0      0   
1005 trnet 101005     1500  –      –      –        ibm  –        0      0   

Primary Secondary Type              Ports
——- ——— —————– ——————————————

Switch#


Normal VLAN

1 – 1001

  • Can be advertised with VTPv1 and 2
  • Configured in vlan database, global config
  • Details stored in vlan.dat
  • Can be pruned

1002 – 1005 Special uses

  • Cannot be pruned
  • 1002 fddi-default
  • 1003 token-ring-default
  • 1004 fddinet-default
  • 1005 trnet-default

Extended VLAN

1006 – 4094

VTPv1 and 2 must be in transparent mode


Voice VLAN

Enables access ports to carry traffic from an IP Phone

  • Portfast is automatically enabled when voice vlan is configured
    • Not disabled if voice vlan is removed

Configure how the Cisco IP Phone carries voice traffic:

  • vlan-id —Configure the phone to forward all voice traffic through the specified VLAN. By default, the Cisco IP Phone forwards the voice traffic with an IEEE 802.1Q priority of 5. Valid VLAN IDs are 1 to 4094.
  • dot1p —Configure the phone to use IEEE802.1p priority tagging for voice traffic and to use the default native VLAN (VLAN 0) to carry all traffic. By default, the Cisco IP Phone forwards the voice traffic with an IEEE 802.1p priority of 5.
  • none —Allow the phone to use its own configuration to send untagged voice traffic.
  • untagged —Configure the phone to send untagged voice traffic.

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