How VLANS addresses drawbacks of LANS

Let us understand how VLANs are better than LANs by using a simple topology as mentioned below

As you can see from the below topology that on the left-hand side of an L3 router we have internet connectivity meanwhile on the right-hand side we have a subnet A with network id as

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From the above topology, the L3 router has a physical interface (IFR) which host subnet  A, and subnet A host three machines A, B, C

So,  when can we say a set of machines are present in local area network(LAN)

A set of machines will be in the local area  network when it satisfies two conditions as mentioned below

  1. All the assigned IP address of machines falls in the same subnet
  2. All the machines should be connected to the same physical wire

Therefore, we can say that the machines A, B, C from the above topology forms a local area network(LAN)


Because it satisfies the above two conditions

As you see the host machines A, B, C, are in the same subnet and they are connected to the same physical wire

Remember: LAN is an outdated technology and VLANs has taken over it

# First drawback

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The first drawback that we have with LAN  is immobility

So, what exactly does that mean?

As you can see from the above topology that we have an L3 router with one physical interface(IFR) which have a subnet whose network id is, let us call this a local area network

The LAN in the above topology contains three host machines A, B, C

At this instant suppose you would like to place machine A in a different subnet

Is it possible?

If you would like to move machine A into a different subnet then you need to change the IP address ( is configured on machine A

Suppose if you changed the IP address of machine A to then machine A will not fall in the same subnet therefore wrong configuration occurs

So, the only way by which you can move machine A to a different subnet is to move machine A physically

As you can see from the below topology that the machine A has physically moved from LAN1 to LAN2

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Moving the machine physically means you need to re-cable the wires to place the machine in a different subnet, And also Re-cabling the network will be a big problem for a network administrator

Moreover, L3 routers  are expensive and have a limited no of physical interfaces,

 To move the host A into a different subnet   you actually consuming one more physical interface of an L3 router

Finally, LANS won’t have the flexibility to move the host machine from one subnet to another subnet without requiring to re-cable the entire network

#second  drawback

The second drawback that is associated with LAN is related to security

To explain the drawback of LAN let us consider that govt library is there where regular visitors will arrive some are temporary visitors and some are regular employees of the library who manage the library

So, the problem arises, when all the visitors are connected to the same physical LAN then they would have equal access to library resources unless restrictions are made per user level

Finally, the library management doesn’t like to grand permission or privileges to the resources for  temporary visitors which library usually grand to regular employee

Vlans (virtual local area network)

Vlans solves the problem of Lans immobility and security

Moreover, Vlan is a Layer 2 concept that can be implemented by using an L2 switch

Vlans allows different machines which are connected to the same physical wire to reside in a different subnet

So, for example, consider the below topology where Vlan allows machine A to be in subnet P meanwhile the machines B and C reside in a subnet Q

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As you can see from the above topology that there is no need to move machine A to another interface   of an L3 router and all the machines which  are present in the topology can be placed in the different subnet using the concept called Vlans

As we have discussed the security issue of Lan with an example case of a library but certainly we can solve that issue by using Vlans  for instance you can host machines B and C with subnet Q for temporary visitors of the library meanwhile machine A with subnet P could be used by the library management team

So, with the help of Vlan both the subnet performs logically different functions

Mohammed Anees

Hey there, welcome to aneescraftsmanship I am Mohammed Anees an independent developer/blogger. I like to share and discuss the craft with others plus the things which I have learned because I believe that through discussion and sharing a new world opens up

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