- A
Create an SD-WAN rule for VoIP traffic with strategy 'best quality' and set the SLA target for latency to 10ms on the MPLS link.
Why wrong: This would only use MPLS if it meets SLA; if not, it might use Internet even if MPLS is up.
- B
Create an SD-WAN rule for VoIP traffic with strategy 'load balancing' and assign equal weight to both links.
Why wrong: Load balancing would distribute traffic, not exclusively use MPLS.
- C
Create an SD-WAN rule for VoIP traffic with strategy 'manual' or 'prefer' and select MPLS as the preferred member, with Internet as backup.
This ensures MPLS is used primarily and Internet only if MPLS is down.
- D
Create an SD-WAN rule for VoIP traffic with strategy 'best quality' and set the SLA target to prefer the Internet link.
Why wrong: This would prefer the Internet link if it meets SLA, not MPLS.
NSE4 High Availability and Diagnostics Practice Question
This NSE4 practice question tests your understanding of high availability and diagnostics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 network engineer is configuring SD-WAN on a FortiGate with two WAN links: MPLS (port1) and Internet (port2). The MPLS link has lower latency and jitter. The engineer wants to route all VoIP traffic (SIP and RTP) over the MPLS link unless it is unavailable. Which SD-WAN rule configuration should be used?
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
Create an SD-WAN rule for VoIP traffic with strategy 'manual' or 'prefer' and select MPLS as the preferred member, with Internet as backup.
Option C is correct because the engineer requires a deterministic routing policy where VoIP traffic always uses the MPLS link unless it fails. The 'manual' (or 'prefer') strategy in SD-WAN rules allows you to explicitly set a preferred member (MPLS) and designate the other link (Internet) as a backup, ensuring failover only when the preferred link is unavailable. This matches the requirement of routing all VoIP traffic over MPLS unless it is unavailable, without relying on SLA performance metrics.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create an SD-WAN rule for VoIP traffic with strategy 'best quality' and set the SLA target for latency to 10ms on the MPLS link.
Why it's wrong here
This would only use MPLS if it meets SLA; if not, it might use Internet even if MPLS is up.
- ✗
Create an SD-WAN rule for VoIP traffic with strategy 'load balancing' and assign equal weight to both links.
Why it's wrong here
Load balancing would distribute traffic, not exclusively use MPLS.
- ✓
Create an SD-WAN rule for VoIP traffic with strategy 'manual' or 'prefer' and select MPLS as the preferred member, with Internet as backup.
Why this is correct
This ensures MPLS is used primarily and Internet only if MPLS is down.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create an SD-WAN rule for VoIP traffic with strategy 'best quality' and set the SLA target to prefer the Internet link.
Why it's wrong here
This would prefer the Internet link if it meets SLA, not MPLS.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'best quality' with a manual preference, assuming that setting a low latency SLA target on MPLS will force all traffic to that link, but 'best quality' can still switch to another link if SLA thresholds are not met, even if the preferred link is operational.
Detailed technical explanation
How to think about this question
In FortiGate SD-WAN, the 'manual' strategy (also called 'prefer' in some versions) uses a static priority list where you assign a preferred member and optionally a backup; the rule will always use the preferred member if it is reachable (based on interface status or route availability), with no SLA probing required. This contrasts with 'best quality', which uses SLA targets (e.g., latency, jitter, packet loss) measured by performance SLA probes to dynamically select the best link, making it unsuitable for a strict 'use this link unless dead' policy. In real-world deployments, VoIP traffic (SIP and RTP) is sensitive to jitter and latency, so a deterministic failover to a backup link (e.g., Internet) ensures service continuity without unnecessary flapping due to minor SLA fluctuations.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this NSE4 question test?
High Availability and Diagnostics — This question tests High Availability and Diagnostics — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create an SD-WAN rule for VoIP traffic with strategy 'manual' or 'prefer' and select MPLS as the preferred member, with Internet as backup. — Option C is correct because the engineer requires a deterministic routing policy where VoIP traffic always uses the MPLS link unless it fails. The 'manual' (or 'prefer') strategy in SD-WAN rules allows you to explicitly set a preferred member (MPLS) and designate the other link (Internet) as a backup, ensuring failover only when the preferred link is unavailable. This matches the requirement of routing all VoIP traffic over MPLS unless it is unavailable, without relying on SLA performance metrics.
What should I do if I get this NSE4 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This NSE4 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE4 exam.
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