Ethernet LAN Switching

Question 1

Functions of Switches in Networks for:

1. Home LAN
2. Corporate LAN
3. Data Centre(DC) LAN

Answer 1

1. Connect home end devices
2. Connects campus end devices
3. Connects DC Servers

Question 2

In general, what does a switch do?

Answer 2

Frame forwarding to correct destination

Question 3

Major functions of a switch?

Answer 3

1. Forwarding Decisions:
   a. Receives frame then looks at destination hardware address and finds exit interface in MAC database
   b. The frame will only be forwarded out the specified destination port
2. Address Learning:
   a. Layer 2 switches and bridges remember the source hardware address of each frame received on an interface
   b. Enters this information into a MAC database called a forward/filter table
3. Loop Avoidance:
   a. If multiple connections between switches are created for redundancy purposes, network loops can occur
   b. Spanning Tree Protocol(STP) is used to stop network loops while permitting redundancy

Question 4

How does a switch do Address Learning?

Answer 4

1. Switches don’t ask hosts for MAC
2. Hosts don’t directly advertise MAC
3. Switches learn through passive learning

Question 5

What is FLOODING in terms of switches?

Answer 5

Sending frames out to all ports (except the incoming port)

Question 6

What is a broadcast storm?

Answer 6

Flood of endless broadcast packets using up significant parts of the capacities of the links

Question 7

What is STP?

Answer 7

Spanning Tree Protocol

Question 8

What does STP do?

Answer 8

1. Stops loops in layer 2 switched networks
   Layer 2 Protocol
2. Uses Spanning Tree Algorithm
   STP: IEEE 802.1D
3. Stops:
   a. Broastcast Storms
   b. MAC table instability
   c. Multiple frame transmission

Question 9

How does STP break loops?

Answer 9

Logically blocks a port to break the loops in the LAN

All switches run STP.

Question 10

Steps of STP:

Answer 10

1. All switches run STP
2. Root switch is elected as common reference point
3. Every other switch finds the best way (port) to send frames to the root switch
4. Using SPA, only required ports are kept open for regular (data) frames
5. Other ports blocked only STP protocol PDUs are allowed