CCNA: Cisco Certified Network Associate — Question 238

How does STP prevent forwarding loops at OSI Layer 2?

Answer options

• A. TTL
• B. MAC address forwarding
• C. Collision avoidance
• D. Port blocking

Correct answer: D

Explanation

The correct answer is D, as Spanning Tree Protocol (STP) prevents loops by blocking certain ports on a switch to create a loop-free topology. The other options do not relate directly to how STP operates; TTL is related to packet lifespan, MAC address forwarding pertains to how switches direct traffic, and collision avoidance is not a function of STP.