A Virtual Local Area Network or VLAN is a way to logically break up broadcast domains.
VLAN = Subnet = Broadcast Domain
When using multiple switches, you have to ensure that the VLAN is configured on any switch that will use the VLAN. Since a VLAN defines broadcast domains in a Layer 2 network, in order to pass traffic from one VLAN to another, you must use routers or Layer 3 switches.
A VLAN is configured in global configuration mode using the vlan keyword. VLAN configuration is stored in a vlan.dat file, not in the running-config or startup-config files.
Switch# configure terminal Switch(config)# vlan vlan_ID Switch(config-vlan)# end
- VLAN 1 is the Cisco default; it is created for you and cannot be deleted.
- VLAN 2 – VLAN 1001 are used for Ethernet VLANs; these can be created and deleted
- VLAN 1002 – VLAN 1005 are defaults for FDDI and Token Ring; these cannot be deleted.
- VLAN 1006 – VLAN 4094 are considered in the extended range and are for Ethernet VLANs only. These will not be propagated by VLAN Trunking Protocol (VTP) and also will not be saved to the VLAN database unless in VTP transparent mode.
Switch# show vlan [id | name] vlan_name
Oddly enough, the Cisco exam objectives for ICND2 call out troubleshooting VLANs. While at this point there is not much for troubleshooting besides verifying that you have created VLANs, the troubleshooting objective will be necessary after further configurations have been made, such as after assigning an interface to a VLAN or with VLAN Trunking Protocol (VTP). There are no specific commands, per se, to aide in troubleshooting.