VLANs

Question 1

What is the purpose of STP (Spanning Tree Protocol)?

Answer 1

Prevents problems caused by loops in a network.

Manages redundant paths and activates them when main path fails or is changed.

Question 2

Process of STP? (Detailed)

Answer 2

Bridges (Switches) running STP:
- Participate with other bridges in the elction of a single bridge as the Root Bridge.

• Calculate the distance of the shortest path to the Root Bridge and choose a port (known as the Root Port) that provides the shortest path to the Root Bridge
• For each LAN segment elect a Designated Bridge and a Designated Port ton that bridge. The Designated Port is a port on the LAN segment that is closest to the Root Bridge (All ports on the Root Bridge are Designated Ports)
• Select bridge ports to be included in the spanning tree. The ports selected are the Root Ports an dDesignated Ports. these ports forward traffic. Other ports block traffic.

Question 3

Process of STP (Brief)

Answer 3

• Election of Root Bridge
• Calculate shortest path to Root Bridge and choose its Root Port
• Each LAN segment, elect Designated Bridge and a Designated port on that bridge which is closest to the Root Bridge.
• Select bridge ports to be included in Spanning Tree. (Ports selected are Root Ports and Designated Ports which forward traffic)

Question 4

How is a Spanning Tree reconfigured when a path fails or is changed?

Answer 4

Using IEEE 802.1w - Also known as RSTP

Question 5

How do bandwidth and throughput differ?

Answer 5

Bandwidth is the maximum amount of data that can travel through a ‘channel’.

Throughput is how much data actually does travel through the ‘channel’ successfully. This can be limited by a number of things including latency and the protocol being used.

Question 6

What are the types of VLAN?

Answer 6

Port based
MAC based
Protocol based

Question 7

Explain the Purpose of the 802.1Q protocol

Answer 7

The 802.1Q Protocol is used when VLANs are split accross more than one switch.

The sending switch adds a tag to the packet which identifies which VLAN it belongs to (if any) and then is stripped by the destination switch.

Can use fields of tag to prioritise certain types of data such as voice data.

Question 8

Why should you be concerned by the number of devices on a single LAN?

Answer 8

With any single shared media LAN segment, transmissions propagate through the entire segment. As traffic activity increases, more collisions occur and transmitting nodes must back off and wait before attempting the transmission again. While the collision is cleared, other nodes must also wait, further increasing congestion on the LAN segment. Reducing throughput.

By splitting a broadcast domain into multiple, smaller domains using VLANs, you can reduce network overhead and reduce data traffic competition.