VLANS Basics

Lets understand  this topic by asking questions to ourselves.

Q1. What is a VLan ??

In a simple language a  virtual local area network (VLAN) is a logical group of workstations (or different network devices) that appear to be on the same LAN despite their geographical distribution.

A VLAN allows a network of computers and users to communicate in a confined environment as if they exist in a single LAN and are sharing a single broadcast and multicast domain.

Q2. Now why do we use VLANs ?

• VLANs are implemented to achieve scalability, security and ease of network management.

• Users don't have to be grouped physically together , they can be grouped logically using different vlan on a same switch thereby we are reducing the device cost too (if we never had this concept we need different devices for different groups.)

• The purpose of implementing a VLAN is to improve the performance of a network or apply appropriate security features. 

Some points to be noted about VLANs : 

• VLAN separates a Layer 2 switch  into multiple broadcast domains.
• Individual ports of group of ports can be assigned to a specific VLAN.
• Only ports belonging to the same VLAN can freely communicate to each other.
• A router or layer-3 switch is need for inter VLAN communication.
• Broadcasts from one VLAN will never be sent out to ports belonging to another vlan.
• By default on a Cisco catalyst switches , all interfaces belong to VLAN is considered the management VLAN (by default)