Hi,

The subnet is a three-layer concept, which refers to the division of IP addresses by borrowing host bits to use as network bits, also known as variable-length subnet masks. After an IP address is divided into subnets,  the subnets actually belong to different networks, and the communication between them needs the support of Layer 3 devices.

And VLAN is a layer 2 concept. It divides a large broadcast domain into more small broadcast domains. A VLAN is a broadcast domain. Since the communication between computers is actually realized by MAC address, so if a computer in one VLAN wants to communicate with a computer in another VLAN, it will broadcast ARP packets and ask for the "MAC address of the destination host". But at this time, the broadcasted ARP packets cannot reach another VLAN, because a VLAN is a broadcast domain, broadcast packets can't reach another broadcast domain, so the communication between different VLANs also need Layer 3 devices to achieve.

Hi!

A subnetwork or subnet is a logical subdivision of an IP network. This results in the logical division of an IP address into two fields: the network number or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.

Each computer - or host - on the internet has at least one IP address as a unique identifier. Organizations will use a subnet to subdivide large networks into smaller, more efficient subnetworks. One goal of a subnet is to split a large network into a grouping of smaller, interconnected networks to help minimize traffic.

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

By logically grouping users into the same virtual networks, you make it easy to set up and control your policies at a group level. When users physically move workstations, you can keep them on the same network with different equipment.