8.2. Quick Reference Decision Trees

💡 First Principle: When you're stuck on an exam question, decision trees help you narrow down the answer systematically. Instead of guessing among four similar-looking options, you ask yourself a series of yes/no questions that eliminate possibilities. Think of it like the 20 Questions game—each question cuts the remaining possibilities in half.

What happens without a systematic approach: You see four plausible answers and panic. You pick one based on gut feeling. Wrong. You change it. Also wrong. With 100+ questions and limited time, random guessing fails. But a decision tree gives you confidence: "I checked Layer 1, Layer 2, Layer 3—the problem must be at Layer 4." Even when uncertain, you can eliminate wrong answers systematically.

Consider this exam scenario: The question describes a network problem. The answers are "check the cable," "check the VLAN," "check the route," and "check the application." The decision tree guides you: Is the link light on? (Layer 1) → Is the MAC table correct? (Layer 2) → Is there a route? (Layer 3). This approach prevents the panicked "all four seem possible!" feeling.

Which Layer? (OSI)

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Which Routing Protocol?

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Which NAT Type?

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