VLAN is a logical grouping of networking devices. It ( Allows us to split switches into Seperate (Virtual ) Networks
- When we create VLAN, we actually break large broadcast domain in smaller broadcast domains. Consider VLAN as a subnet.
- Same as two different subnets cannot communicate with each other without router, different VLANs also requires router to communicate.
- Only members of a VLAN can see that VLAN’s traffic
- Inter-VLAN traffic must be routed (i.e. go through a router) because they are separate subnets.
Advantage of VLAN
VLAN provides following advantages:-
- Solve broadcast problem
- Reduce the size of broadcast domains
- Allow us to add additional layer of security
- Make device management easier
- Allow us to implement the logical grouping of devices by function instead of location.
Solve broadcast problem
When we connect devices into the switch ports, switch creates separate collision domain for each port and single broadcast domain for all ports. Switch forwards a broadcast frame from all possible ports. In a large network having hundreds of computers, it could create performance issue. Of course we could use routers to solve broadcast problem, but that would be costly solution since each broadcast domain requires its own port on router. Switch has a unique solution to broadcast issue known as VLAN. In practical environment we use VLAN to solve broadcast issue instead of router.Each VLAN has a separate broadcast domain. Logically VLANs are also subnets. Each VLAN requires a unique network number known as VLAN ID. Devices with same VLAN ID are the members of same broadcast domain and receive all broadcasts. These broadcasts are filtered from all ports on a switch that aren’t members of the same VLAN.Reduce the size of broadcast domains
VLAN increase the numbers of broadcast domain while reducing their size. For example we have a network of 100 devices. Without any VLAN implementation we have single broadcast domain that contain 100 devices. We create 2 VLANs and assign 50 devices in each VLAN. Now we have two broadcast domains with fifty devices in each. Thus more VLAN means more broadcast domain with less devices.Allow us to add additional layer of security
- VLANs enhance the network security. In a typical layer 2 network, all users can see all devices by default. Properly configured VLANs gives us total control over each port and users. With VLANs, you can control the users from gaining unwanted access over the resources. We can put the group of users that need high level security into their own VLAN so that users outside from VLAN can’t communicate with them.
Make device management easier
Device management is easier with VLANs. Since VLANs are a logical approach, a device can be located anywhere in the switched network and still belong to the same broadcast domain. We can move a user from one switch to another switch in same network while keeping his original VLAN. For example our company has a five story building and a single layer two network. In this scenario, VLAN allows us to move the users from one floor to another floor while keeping his original VLAN ID. The only limitation we have is that device when moved, must still be connected to the same layer 2 network.
