17 - Vlans

Question 1

What is a Vlan

What does it do ?

What does this effectively mean for devices ?

Answer 1

Vlan stands for = Virtual LANs

-Vlan helps breaks up a broadcast domain into multiple Virtual/Logical groups
( keeps Separation between broadcast domains by making them into groups )

• Logically grouping devices
• into the same broadcast domain
• by placing the device interfaces into a Vlan of our choice.

This means only ports within the same VLAN will only only be able to communicate with each other. (broadcast only to each other)
Unless it is helped by a Router or layer 3 device.

Question 2

Do you have to be connected to the same switch to be in the same Vlan ?

Answer 2

Vlans allows hosts to be grouped together in the same (vlan)broadcast domain even if they are not connected to the same switch

e. g a broadcast will reach every device on all switches that are on the same vlan
e. g vlan 15, all devices across 4 connected switches will hear the broadcast if on the same vlan

Question 3

What is the Maximum Number of Vlans allowed on a switch ?

Answer 3

Maximum = 4096

Question 4

What Vlans can not be used?

and how many are they ?

Answer 4

VLANs 1002-1005 are default VLANs for FDDI & Token Ring and they can’t be deleted or used for
Ethernet.

amounts is = 4

Question 5

Do devices in the same Vlan have to have the same ip subnet ?

Answer 5

Each vlan will require their own subnet
- different to other vlans.

Every device on the same vlan will have to be in the same subnet

Question 6

Do vlans increase broadcast domain size ?

Does that mean there are fewer broadcast domain due to vlans ?

Answer 6

• VLANs increase the number of broadcast domains
  (not the size)
• while decreasing their size.

So No to both questions

Question 7

when their is a broadcast all ports are flooded,

do all vlans receive the flooded broadcast ?

Answer 7

VLANs reduce security risks by reducing the number of hosts that receive broadcast frames that the switches flood, by sending it only to the relevant vlan

Question 8

Should you group user into the same vlan based on their physical location ?

Answer 8

you can create more flexible network designs by grouping users by department instead of by physical location