Lessons · Network switches · VLANs live outside the config

The VLAN database is not part of the configuration

In the default VTP mode a switch keeps its VLANs in vlan.dat on flash -- not in the running configuration, and not in NVRAM.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

One fact explains three surprises: a config backup does not carry the VLANs, `erase startup-config` does not remove them, and a reload does not undo deleting one.

How to think about it

Treat the VLAN list as a separate thing to record and a separate thing to wipe. `show vlan brief` is where it lives; the configuration is not.

Worked example

enable

In.

configure terminal

Make a VLAN with a name.

vlan 40

Created.

name PACKING

Named. This name is the part that will not travel.

exit

Out of the VLAN.

exit

And out of config mode.

show vlan brief

There it is, with its name. This reads the database.

show running-config | include PACKING

And nothing comes back. The name is not in the configuration.

dir flash:

vlan.dat, on the disk, which is where it actually is.

Your turn

List the VLANs on this switch with their names.

show vlan

The trap

Handing a switch on after `erase startup-config` and a reload. It comes back with no configuration and every VLAN somebody made on it.

Practise VLANs live outside the config on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.