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What is Vlan and How it Helps Us in Switching ..?


Posted by WebUser Swaroop BigBoy from Cisco Support Community App

VIP Expert


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Cisco Employee

Simple words:

VLAN is a single broad cast domain. For example to avoid the broadcast flowing across your network you byforgate to specific domain which is know as vlan.

Eg: Consider a small company were you have 3 departments( Technical, Sales,HR) by default if you dont have vlan on switches, then the packet would be broadcasted to all the ports on the switch by default.(I mean to say if Technical guy wants to speak toanother technical guy sitting beside him if we dont have vlan then the packet would be flooded across to Technical,Sales and HR which we dont need, unnecessary broadcast and the packet reaching to people who doesnt need. Hence you device this single broadcast to sub broadcast domain wich is known as vlan.)





Vlan also known as Virtual Local Area Network is just as the name implies, creating several "virtual LANs" on a single switch. It helps in the segmentation of the broadcast domian as a broadcast cannot be propagated to other VLANs on the network except the one it originates from. It is also useful for securing the network to  SOME extent.

Hope this helps.


Hi Swaroop,

Could you please check this and let us know if you are not satisfied with the answerd posted if yes then let us know what infomration you required so that we help you outl ifn no can you please mark the thread as answered.



VIP Mentor

Hi Swroop,

“A virtual LAN (VLAN) is a group of networking devices in the same broadcast domain, logically”

It means that the devices in the same VLAN may be widely separated in  the network, both by geography and location. VLANs logically segment  the network into different broadcast domains so that packets are only  switched between ports that are designated for the same VLAN.

For details explantaion with example, u can visit this website:


Hope it helps.


VLANs (Virtual Local Area Networks) are created to seperate layer 2 traffic.Generall types of traffic include.

1. Multicast (Video streaming)

2. Network Management Traffic (SNMP messages, CDP Messages, BPDU's etc)

3. VoIP (Voice Traffic)

4. User traffic

So let us assume there are no VLANs, what happens here is: Since the basic functinality of a switch is to flood if the destination MAC address is not present in its CAM table (And also if it's cam table is full).. we will see a lot of broadcast messages all of the above said usages.

And also let us take the example of the VoIP ... since there are no VLANs and switch is expereincing a lot of broadcast messages and the users are using VoIP obviously some of the packets will drop because of the broadcast storm that switch is experiencing. So there will be a lot of disturbance in that call.. And same thing applies all the above types of traffic.

So inorder to overcome the above issues we need seperate the traffic types which means broadcast domains by creating virtual LANs.. in this way VLANs seperate layer 2 traffic to enhance stability and security.

Agian how securty is achieved : simple inorder to communicate between two VLANs you need a layer3 device (a router) where we cann assign ACLs like which VLANs traffic to pass or bypass it.

And also VLANs are location independent it means it can span to multiple switches.. untill the user belong to the same VLAN he can communicate with the members in same VLAN without using layer3 device....

And also excellent info is availbale @ :

Please rate.



Regards, Chandu
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