Clearing Cisco Switch VLANs

Background

Because of VLAN Trunking Protocol (VTP) which will automatically create (or re-create) VLANs on a switch based on the configuration of other switches it can be tricky to clear the VLANs from a switch when other switches are running on the network. These instructions can be followed to clear VLANs from environments with multiple switches which may be running VTP.

Clearing ALL VLANs and VTP settings switches

Complete the following steps on EACH switch you wish to reset:

If you want to keep the existing configuration (other than VLANs) be sure to save your running-configuration on each switch before proceeding!
1. Enter privileged EXEC mode with the enable command
2. Enter global configuration mode with the configure terminal command
3. Set the VTP mode to transparent with the vtp mode transparent command
4. Exit global configuration mode with the exit command
5. Delete the vlan.dat file with the delete flash:vlan.dat command. Press the enter key to confirm the filename to delete is vlan.dat (do not press Y, just press enter) and the enter key again to confirm you want to delete flash:/vlan.dat
  Switch#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#vtp mode transparent Setting device to VTP Transparent mode for VLANS. Switch(config)#exit Switch# *Sep 18 13:32:51.205: %SYS-5-CONFIG_I: Configured from console by console Switch#delete flash:vlan.dat Delete filename [vlan.dat]? Delete flash:/vlan.dat? [confirm] Switch#

After the above steps have been done to all switches restart each switch using the reload command. Do not save changes the running configuration and confirm you want to reload the switch.

Switch#reload

System configuration has been modified. Save? [yes/no]: no
Reload command is being issued on Active unit, this will reload the whole stack
Proceed with reload? [confirm]

After all switches reboot verify that only the default VLANs exist with the show vlan brief command. The exact output will depend on the switch, for example:

Switch#show vlan brief

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
                                                Fa0/5, Fa0/6, Fa0/7, Fa0/8
                                                Fa0/9, Fa0/10, Fa0/11, Fa0/12
                                                Fa0/13, Fa0/14, Fa0/15, Fa0/16
                                                Fa0/17, Fa0/18, Fa0/19, Fa0/20
                                                Fa0/21, Fa0/22, Fa0/23, Fa0/24
                                                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
Switch#

Verify that the VTP domain name is blank, the VTP mode is Server, and the configuration revision number is 0 using the show vtp status command. Exact output may vary from one switch model to another, for example:

Switch#show vtp status
VTP Version capable             : 1 to 3
VTP version running             : 1
VTP Domain Name                 :
VTP Pruning Mode                : Disabled
VTP Traps Generation            : Disabled
Device ID                       : 003a.7db0.d780
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00
Local updater ID is 0.0.0.0 (no valid interface found)

Feature VLAN:
--------------
VTP Operating Mode                : Server
Maximum VLANs supported locally   : 1005
Number of existing VLANs          : 5
Configuration Revision            : 0
MD5 digest                        : 0x57 0xCD 0x40 0x65 0x63 0x59 0x47 0xBD
                                    0x56 0x9D 0x4A 0x3E 0xA5 0x69 0x35 0xBC
Switch#

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