Networking
Guess first
What Does a Switch Do With an Unknown MAC?
Most students get this wrong about how a switch forwards frames.
Quick check · tap an answer to continue
Lesson notes
Key points
- When a switch has no MAC table entry for the destination, it floods the frame out every port except the one it arrived on.
- Meanwhile it records the sender's source MAC against the incoming port, so replies go out only one port next time.
Takeaway: Switches learn from source MACs and flood unknown destinations.
Quick check: A switch receives a frame for a MAC address not in its table. What does it do?
- Drops the frame
- Sends an ARP request
- Floods all other ports
Unknown destination MAC means flood; source MAC means learn.
FloodingMAC learning
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