Network fundamentals
⏱ ~3-min readAceMark Guide
What this topic is really about
When a switch sees an unknown unicast destination MAC, it floods the frame out every port in the VLAN except the inbound port. This is called unknown unicast flooding and is how switches learn destinations. ARP is a Layer 3 host mechanism, not a switch one.
Link-local IPv6 addresses use the FE80::/10 prefix and are valid only on a single link, used for neighbor discovery and next-hop routing. Global unicast typically starts with 2000::/3, unique local with FC00::/7, and multicast with FF00::/8.
See the mechanism
When a switch sees an unknown unicast destination MAC, it floods the frame out every port in the VLAN except the inbound port. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.
An exam-style question, fully explained
A switch receives a frame whose destination MAC address is not in its MAC address table. What does the switch do?
- Identify what the question tests: A switch receives a frame whose destination MAC address is not in its MAC address table..
- When a switch sees an unknown unicast destination MAC, it floods the frame out every port in the VLAN except the inbound port.
- This is called unknown unicast flooding and is how switches learn destinations.
- ARP is a Layer 3 host mechanism, not a switch one.
Traps the examiner sets
- Read each option carefully — distractors on Network fundamentals are designed to look plausible.
- Re-check the exact wording of the question stem before committing to an answer.
- Watch the qualifiers ("always", "only", "except") that flip a correct-looking option.
Test your recall
Answer each from memory — you'll see instantly whether you're right and why.
Run a focused 10-question mini-mock on Network fundamentals and see it stick.
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