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Cisco switches keep VLAN information in a separate file — `vlan.dat` in flash — not in the running config. This is the single most surprising thing about VLANs, and it's the reason `erase startup-config` doesn't clear VLANs.
! Create VLANs with namesSwitch1(config)# vlan 10Switch1(config-vlan)# name SalesSwitch1(config-vlan)# exitSwitch1(config)# vlan 20Switch1(config-vlan)# name EngineeringSwitch1(config-vlan)# exitSwitch1(config)# vlan 99Switch1(config-vlan)# name ManagementSwitch1(config-vlan)# exit! VerifySwitch1# show vlan brief
VLAN names are optional but recommended. A VLAN with a name is self-documenting; a VLAN without is a mystery six months later when someone asks why VLAN 47 exists. Make naming a habit.
That `vlan.dat` holds the VLAN database. When you create a VLAN, it goes there — not into startup-config. This is why `show running-config` on a switch doesn't show `vlan 10` lines in older IOS — they live in a separate file.
On newer IOS versions (IOS-XE), VLANs may appear in running-config. On classic IOS (most Catalyst 2960/3560), they live in vlan.dat. If you're doing VLAN cleanup on a device that stores VLANs in vlan.dat, you must delete the file: `delete flash:vlan.dat`.
Switch1(config)# no vlan 20Switch1(config)# exitSwitch1# show vlan brief
Deleting a VLAN removes it from the database. Any ports still assigned to it go inactive (`inactive` state) until you reassign them. If a trunk is carrying that VLAN, the traffic stops flowing for that VLAN.
Don't delete VLAN 1. It can't be deleted — the switch rejects the command. Don't delete VLANs that are in active use without checking what's on them first. The Cisco IOS has no `--force` flag; it just does what you tell it, even if that breaks your network.
`Administrative Mode: static access` confirms this is a fixed access port. `Access Mode VLAN: 10 (Sales)` shows the assignment. If the port were negotiating trunking, `Administrative Mode` would say `dynamic auto` or `dynamic desirable` — one to watch for, because DTP negotiation is a security concern.
VLAN database mechanics understood. Next lesson: voice VLANs and how IP phones coexist with workstations on one port.
Finish the lesson once you have worked through the material. This awards ★ 30 XP.