In the figure, the no vlan vlan-id global configuration mode command is used to remove VLAN 20 from the switch. Switch S1 had a minimal configuration with all ports in VLAN 1 and an unused VLAN 20 in the VLAN database. The show vlan brief command verifies that VLAN 20 is no longer present in the vlan.dat file after using the no vlan 20 command.
Caution: Before deleting a VLAN, be sure to first reassign all member ports to a different VLAN. Any ports that are not moved to an active VLAN are unable to communicate with other hosts after the VLAN is deleted and until they are assigned to an active VLAN.
Alternatively, the entire vlan.dat file can be deleted using the delete flash:vlan.dat privileged EXEC mode command. The abbreviated command version (delete vlan.dat) can be used if the vlan.dat file has not been moved from its default location. After issuing this command and reloading the switch, the previously configured VLANs are no longer present. This effectively places the switch into its factory default condition concerning VLAN configurations.
Note: For a Catalyst switch, the erase startup-config command must accompany the delete vlan.dat command prior to reload to restore the switch to its factory default condition.