Analyzing Ethernet LAN Switching

Question 1

LAN Switch role

Answer 1

To forward frames to the correct destination (MAC) address. And to achieve that goal, switches use logic—logic based on the source and destination MAC address in each frame’s Ethernet header.

Question 2

LAN Switching decision

Answer 2

1. Deciding when to forward a frame or when to filter (not forward) a frame, based on the destination MAC address
2. Preparing to forward frames by learning MAC addresses by examining the source MAC address of each frame received by the switch
3. Preparing to forward only one copy of the frame to the destination by creating a (Layer 2) loop-free environment with other switches by using Spanning Tree Protocol (STP)

Question 3

Switch’s MAC address table aliases

Answer 3

• Switching table
• Bridging table
• Content-Addressable Memory (CAM) table

Question 4

Learning MAC Addresses

Answer 4

The switch learns the MAC Address by listening to incoming frames and examining the source MAC address in the frame

Question 5

Flooding

Answer 5

When there is no matching entry in the table, switches forward the unknown unicast frame out all interfaces (except the incoming interface)

Question 6

Spanning Tree Protocol (STP)

Answer 6

Each interface on a switch is settled into either a blocking state or a forwarding state.
Blocking means that the interface cannot forward or receive data frames, while forwarding means that the interface can send and receive data frames.