350-501 Automation and Quality of Services Practice Question
Which THREE of the following are standard per-hop behaviors (PHBs) in the DiffServ model? (Select three.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Default (Best Effort)
The DiffServ model defines EF (Expedited Forwarding), AF (Assured Forwarding), and Default (BE) PHBs. CS is Class Selector, but not a separate PHB; it is part of AF? Actually CS is a backward-compatible PHB. Standard ones are EF, AF, and Default.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Default (Best Effort)
Why this is correct
Default PHB for best-effort traffic.
- ✗
LLQ
Why it's wrong here
LLQ is a queuing mechanism, not a PHB.
- ✗
CS (Class Selector)
Why it's wrong here
CS is for backward compatibility with IP Precedence, not a separate PHB.
- ✓
AF (Assured Forwarding)
Why this is correct
AF provides four classes with three drop probabilities.
- ✓
EF (Expedited Forwarding)
Why this is correct
EF is a PHB for low-loss, low-latency traffic.
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