Question

1) What is a VLAN? Explain how frames are forwarded between devices in the same VLAN, and between different VLANs

2) Describe the IEEE 802.1Q protocol and how it affects the original Ethernet header. (please draw the IEEE 802.1Q header here to add to your explanation).

Answer 1

• 1.VLANs (Virtual LANs) are logically grouping of devices in the same broadcast domain.
• VLANs are usually configured on switches by placing some interfaces into one broadcast domain and some interfaces into another.
• Each VLAN acts as a subgroup of the switch ports in an Ethernet LAN.
• VLANs can spread across multiple switches ,with each VLAN being treated as its own subnet or broadcast domain.This means that frames broadcasted onto the network will be switched only between the ports within the same VLAN.
• A VLAN acts like a physical LAN ,but it allows hosts to group together in the same broadcast domain even if they are not connected to the same switch.
• To reach the host in a different VLAN,a router is needed.
• 2.IEEE 802.1Q was created to address the problem breaking lagre networks into smaller and mangeable ones through the use of VLANs.
• The 4-byte tag is inserted within the existing Ethernet Frame,right after the Source MAC address .
• Because of the extra 4-byte tag,the minimum Ethernet 11 frame size increases from 64 bytes to 68 bytes,while the maximum Ethernet 11 frame size now becomes 1522 bytes.
• The maximum Ethernet frame is considerably smaller in size (by 26 bytes)..