To enter VLAN configuration mode on a Cisco core switch, use the interface vlan <VLAN_ID> command in global configuration mode.

Step-by-Step Guide

1. Access the Switch CLI
   • Connect to the core switch via console, SSH, or Telnet.
   • Enter privileged EXEC mode:

     enable

   • Enter global configuration mode:

     configure terminal

2. Enter VLAN Interface Mode
   • To configure a specific VLAN, use:

     interface vlan <VLAN_ID> Replace <VLAN_ID> with the VLAN number you want to configure (valid range: 1–2349 and 2450–4093) .

   • This command allows you to configure parameters for that VLAN, such as assigning an IP address for Layer 3 VLANs or enabling routing.
3. Create a VLAN (if it does not exist)
   • If the VLAN is not already created, first create it:

     vlan <VLAN_ID>name <VLAN_NAME> This ensures the VLAN exists before entering interface mode .

4. Assign Ports to the VLAN
   • After entering VLAN interface mode, assign access ports:

     interface <interface_id>switchport mode accessswitchport access vlan <VLAN_ID>

   • For trunk ports carrying multiple VLANs:

     interface <trunk_interface>switchport mode trunkswitchport trunk allowed vlan <VLAN_LIST>

5. Verify VLAN Configuration
   • Use the following commands to check VLAN status:

     show vlan briefshow running-configshow interfaces trunk

   • These commands confirm that the VLAN exists, ports are assigned correctly, and trunk links are passing the VLAN .

Best Practices

• Always create VLANs before assigning ports.
• Use meaningful VLAN names for easier management.
• Verify trunk links to ensure VLANs propagate across switches.
• Avoid native VLAN mismatches on trunk ports to prevent broadcast issues . By following these steps, you can successfully enter and configure VLANs on a core Cisco switch, ensuring proper segmentation and network management.