Difference Between Subnet and VLAN

When you are working in a network, there are times when you need to separate them so that everyone cannot access them. Otherwise, there is no sense of security and privacy. So, in networking, it is essential to understand some important terms which are responsible for separating the network. Two of the most used terms in networking related to this work are a subnet and VLAN. In this post, we will see the difference between subnet and VLAN.

Table of Contents

What is a Subnet?

First of all, let us understand why we require separate networks (Refer to the below image). Suppose there are a large number of devices and all are using the same Ethernet switch for data communication. In that case, it will load the switch and the network, as all the devices will broadcast messages simultaneously and confuse the other devices.

To solve this issue, we use a method called subnet. In the below image, we have separated the whole network into three sub-networks. Each network will have its own Ethernet switch. Due to this, only the devices connected to a local network will broadcast messages within themselves. It will not go outside the network. This is possible through routers.

Routers are devices which physically isolate the network and do not allow mixup of data. If routers are not used, then even though we used different Ethernet switches, data will broadcast everywhere. This is because the switch is just a network extender and it enables a large number of devices to be connected.

Subnet is possible not only through the use of routers, but how an IP address is set for the device. As you know, IP addresses can be set in a computer through the IPv4 address option. It consists of three parts –

IP address,
subnet mask, and
default gateway.

The subnet mask is that portion which tells how many devices can communicate in a particular network. An IP address consists of two parts – network and host. So, the subnet mask will tell us how many devices or hosts can communicate in a network. The hosts which have addresses outside that network cannot broadcast messages in that particular network continuously. So, if it is required to send messages outside the network, it will do this through a router.

A router does not listen to other network’s broadcast messages; it only listens to it’s network broadcast messages. So, if a device in another network wants to send a message, it will be done through the two routers – one in the sender network and the other in the destination network. The sender router smartly sends data to only the destination router and finally, the message is then delivered to the destined device. So, creating a subnet means assigning a subnet mask and using routers in a network.

What is VLAN?

In the very first example where we saw how a single Ethernet switch cannot be used to create different networks, there comes a method where this single switch can be split into different networks. This is possible through the use of a technique called VLAN or virtual LAN.

As the name implies, VLAN creates a separate network virtually and not physically. So, there is no need for extra switches, as we saw in a subnet. VLAN is created by configuring the various ports of the switch as VLAN ports. So, suppose if you want to create three sub-networks within a single switch, then you will configure the required ports into their corresponding networks.

If there are a total of 16 ports and you want 4 ports as network-1, 6 ports as network-2 and 6 ports as network-3, then you have to configure each of the ports accordingly. Due to this, network-1 ports will only communicate within themselves, network-2 within themselves and network-3 within themselves. If they want to send messages outside the network, then routers will be used as a subnet.

VLAN ports are configured by adding an extra 4-byte VLAN tag in the Ethernet frame. The ports of one network will have a common VLAN tag ID and will be different from other network VLAN tags. This will distinguish them from other ports of the network. So when the ports are configured as VLAN ports, the whole switch functions as VLAN and allows different networks to operate within itself and isolates each network with other ones for privacy and security.