VLAN Configuration

1. VLAN Configuration 🗺️ – Separate Teams Logically

Imagine you’re the network administrator of a mid-sized company.

Your task: separate the HR and Sales teams logically, even though their devices are connected to the same physical switch.

Network Setup

2. Creating VLANs on Cisco Switch

Let’s connect to the switch and begin.

1. Enter Global Configuration Mode

SW1# configure terminal

2. Create VLAN 10 (HR)

SW1(config)# vlan 10
SW1(config-vlan)# name HR
SW1(config-vlan)# exit

3. Create VLAN 20 (Sales)

SW1(config)# vlan 20
SW1(config-vlan)# name Sales
SW1(config-vlan)# exit

The VLANs are now created in the VLAN database.

3. Verifying VLAN Configuration

Let’s make sure VLANs have been successfully created.

SW1# show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
£1    default                          active    G0/0, G0/1, G0/2, G0/3, G0/4, G0/5£
£10   HR                               active£    
£20   Sales                            active£    
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup 

Note: All ports are still in VLAN 1 (Default VLAN) for now !

4. Assigning Ports to VLANs

Let’s now assign the correct switch ports to their respective VLANs.

Assign HR Ports: G0/0 – G0/2

SW1(config)# interface range G0/0 - G0/2
SW1(config-if-range)# switchport mode access
SW1(config-if-range)# switchport access vlan 10
SW1(config-if-range)# exit

Assign Sales Ports: G0/3 – G0/5

SW1(config)# interface range G0/3 - G0/5
SW1(config-if-range)# switchport mode access
SW1(config-if-range)# switchport access vlan 20
SW1(config-if-range)# exit

🧠 What’s Happening Here?

• switchport mode access → Forces each interface to operate in access mode, which supports one VLAN only.
• switchport access vlan X → Assigns the specified VLAN ID to the port.

This ensures traffic from each department is logically separated, even though all devices are physically connected to the same switch.

5. Verifying Port Assignments

Let’s verify that the interfaces are assigned to the correct VLANs.

SW1# show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    none
10   HR                               active    G0/0, G0/1, G0/2
20   Sales                            active    G0/3, G0/4, G0/5
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup

✅ VLAN configuration is successful.
🎯 Each department is now logically isolated within the switch.

6. Managing VLAN Configuration on Cisco Switches

Let’s explore how VLANs are saved, modified, or removed in a real switch environment.

📁 What Is vlan.dat ?

When you create a VLAN, the configuration is not stored in the running-config.
Instead, VLANs are saved in a dedicated file called vlan.dat, located in the switch’s flash memory.

Why does it matter?

• ✅ VLANs survive a reboot
• ❌ erase startup-config doesn’t remove them
• 🧹 You must delete vlan.dat to wipe VLANs entirely

✏️ Modify a VLAN (Rename Example)

Suppose you want to rename VLAN 10 from HR to HR_Department.

You need to :

1. Enter VLAN configuration mode:

SW1# configure terminal
SW1(config)# vlan 10
SW1(config-vlan)# name HR_Department
SW1(config-vlan)# exit

2. Rename the VLAN (from “HR” to “HR_Department”):

SW1(config-vlan)# name HR_Department

You can now verify the change with:

SW1# show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    none
£10   HR_Department                    active    G0/0, G0/1, G0/2£
20   Sales                            active    G0/3, G0/4, G0/5
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup

🧹 Removing VLAN Configurations

Here’s a key thing to know:

VLANs are not saved in the running-config or startup-config—they’re stored in a separate file called vlan.dat.

This file is located in the switch’s flash memory, and it keeps all your VLANs persistent across reboots.

🧠 If you want to completely wipe VLAN configurations, you need to delete vlan.dat manually.

Removing VLAN Configurations

1. Delete the VLAN database:

SW1# delete flash:vlan.dat
Delete filename [vlan.dat]? [confirm]

2. Erase the startup configuration:

SW1# erase startup-config

3. Reload the switch:

SW1# reload

⚠️ The switch will reboot and come back with only the default VLAN (VLAN 1).

✅ Verifying the Reset

Once the switch is back online, run:

SW1# show vlan brief

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    G0/0, G0/1, G0/2, G0/3, G0/4, G0/5
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup

✅ Only VLAN 1 remains
❌ VLAN 10, VLAN 20, and any others are gone

👉 Your switch is now clean and ready for a new configuration.

Ready to go further?

➡️ In the next lesson, we’ll configure trunk ports, which allow VLANs to travel between switches—a key concept for scaling your network.

Let’s keep going! 🚀