Lesson 22: Frame Forwarding and Flooding
How a switch decides where to send a frame based on the Destination MAC address.
Forwarding Decisions (Unicast)
- If the Destination MAC is found in the MAC address table, the switch performs Unicast Forwarding, sending the frame only out the corresponding port.
- If the Destination MAC is NOT found (this is called an unknown unicast), the switch performs Flooding. The frame is sent out all ports except the port it was received on.
Flooding (Broadcast and Unknown Unicast)
- Broadcast Frames (FFFF.FFFF.FFFF): Always flooded out all ports. This is necessary for protocols like ARP and DHCP.
- Unknown Unicast: Flooded until the switch learns the location of the destination MAC address.
Collision and Broadcast Domains
- Collision Domain: A network area where collisions can occur. A switch places each port in its own collision domain, eliminating collisions in full-duplex environments.
- Broadcast Domain: A network area where a broadcast frame will reach all devices. By default, an entire switch is one broadcast domain. (We use VLANs to segment broadcast domains.)