The answer is to use priority queuing (LLQ) for EF traffic with a policer. This is correct because Low Latency Queuing (LLQ) provides a strict priority queue that services Expedited Forwarding (EF) packets before any other traffic, which directly reduces jitter by ensuring consistent, low-latency delivery even during congestion; the policer is essential to prevent the priority queue from starving other queues. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of QoS mechanisms in an MPLS backbone, often appearing in a scenario where EF traffic like VoIP suffers from delay variation—a common trap is choosing WRED or shaping, which manage congestion but do not eliminate jitter for real-time flows. Remember the memory tip: “LLQ for EF, police to protect the rest.”
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service provider has deployed QoS on its MPLS backbone to offer different classes of service. The provider notices that EF (Expedited Forwarding) traffic sometimes experiences high jitter during congestion. Following recommended practices, which action is MOST likely to reduce jitter for EF traffic?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use priority queuing (LLQ) for EF traffic with a policer
Option B is correct because priority queuing ensures EF traffic is served before other queues, reducing jitter. Option A is wrong because shaping reduces bandwidth but does not eliminate jitter if congestion exists. Option C is wrong because WRED is for congestion avoidance and can drop EF packets if not excluded. Option D is wrong because changing DSCP does not improve jitter directly; proper queuing is key.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Use priority queuing (LLQ) for EF traffic with a policer
Why this is correct
LLQ gives strict priority, minimizing jitter by servicing EF first.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Apply traffic shaping on all EF packets at the edge
Why it's wrong here
Shaping smooths bursts but does not eliminate jitter under congestion; priority queuing is better.
✗
Change the DSCP value of EF traffic to AF41 to reduce drops
Why it's wrong here
Changing DSCP does not address jitter; proper queuing is required.
✗
Apply weighted random early detection (WRED) on the EF queue
Why it's wrong here
WRED might drop EF packets, causing retransmissions and jitter; not recommended for EF.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Architecture — This question tests Architecture — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use priority queuing (LLQ) for EF traffic with a policer — Option B is correct because priority queuing ensures EF traffic is served before other queues, reducing jitter. Option A is wrong because shaping reduces bandwidth but does not eliminate jitter if congestion exists. Option C is wrong because WRED is for congestion avoidance and can drop EF packets if not excluded. Option D is wrong because changing DSCP does not improve jitter directly; proper queuing is key.
What should I do if I get this 350-501 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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