Ethernet, Switching, and LAN Behavior
LANs and Ethernet Frames
Local delivery
Ethernet is the dominant technology for wired local area networks. It defines how devices format frames, address local peers using MAC addresses, and share a medium through switches.
Why switches matter
A switch forwards frames only to the correct port using its MAC address table, which reduces unnecessary traffic and improves performance compared with hub-based sharing.
MAC addresses
A MAC address is a layer identifier used for delivery within a local broadcast domain. It is not the same as an IP address, which works at layer .
Common LAN Terms
| Term | Meaning |
|---|---|
| Frame | Layer 2 data unit |
| MAC table | Switch lookup table mapping MACs to ports |
| Broadcast domain | Set of devices that receive broadcasts |
| Collision domain | Area where frames may contend for medium |
What does a switch primarily use to decide where to send a frame?
Layer 2 switches forward frames using destination MAC addresses.
Correct answer: MAC address
Why are switches preferred over hubs in modern LANs?
Selective forwarding reduces collisions, congestion, and unnecessary exposure of traffic.
Correct answer: They forward traffic selectively instead of flooding every frame to every device
VLANs and Segmentation
Logical separation
Virtual LANs, or , let administrators split one physical switch infrastructure into multiple logical broadcast domains. This improves security, management, and traffic containment.
What is the main effect of creating separate VLANs?
VLANs segment a switched network into isolated logical groups.
Correct answer: They create separate logical broadcast domains
How a switch learns MAC addresses
-
1
Step 1: A frame arrives on a switch port.
-
2
Step 2: The switch records the source MAC and incoming port.
-
3
Step 3: The switch checks its MAC table for the destination MAC.
-
4
Step 4: It forwards the frame to the known port or floods if unknown.