VLAN

A VLAN (Virtual Local Area Network) is a network within a network that allows the segmentation of devices into different broadcast domains even if they are on the same physical switch. VLANs improve network performance, enhance security, and simplify network management.

Key Concepts of VLANs in Cisco Networking

1. VLAN ID: Each VLAN is identified by a unique VLAN ID, which is a number between 1 and 4094. For example, VLAN 10 could be used for accounting, VLAN 20 for HR, etc.
2. Default VLAN: VLAN 1 is the default VLAN on all Cisco switches. All switch ports are initially in VLAN 1.
3. Access Ports: These are switch ports configured to carry traffic for a single VLAN. A device connected to an access port is assigned to the VLAN configured on that port.
4. Trunk Ports: Trunk ports carry traffic for multiple VLANs between switches. Trunking encapsulates the VLAN information so that devices on different switches can be part of the same VLAN.
5. VLAN Tagging: In trunk links, VLAN tagging is used to identify which VLAN a frame belongs to. The most common tagging protocol is IEEE 802.1Q.
6. VTP (VLAN Trunking Protocol): A Cisco proprietary protocol that propagates VLAN information to all switches in a VTP domain. This helps maintain consistency across the network.

Basic Commands to Configure VLANs on a Cisco Switch

1. Create a VLAN:

Example:

2. Assign a Port to a VLAN:

Example:

3. Configure a Trunk Port:

Example:

4. Verify VLAN Configuration:

This command displays the VLANs configured on the switch and the ports assigned to each VLAN.

5. Remove a VLAN:

Example:

Best Practices

• Use Descriptive VLAN Names: This helps in identifying the purpose of each VLAN.
• Avoid Using VLAN 1: It’s best practice to avoid using the default VLAN for security reasons.
• Plan VLANs Carefully: Proper planning of VLANs in the network helps in easier management and reduces the chance of conflicts or misconfigurations.

These are the fundamental aspects of configuring VLANs on Cisco switches.