NSE4 High Availability and Diagnostics Practice Question
Which THREE statements about SD-WAN rules are correct?
⚠ Common exam trap
Watch out — candidates often assume SD-WAN rules must use load balancing, but Fortinet allows multiple strategies including 'best quality' and 'manual', and they also mistakenly think each rule can only have one member, whereas member groups are supported for redundancy and load distribution.
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
✓
SD-WAN rules are evaluated in order of priority.
SD-WAN rules are evaluated in order of priority, meaning the rule with the highest priority (lowest number) is matched first. This sequential evaluation ensures deterministic traffic steering based on the most specific match criteria defined by the administrator.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
SD-WAN rules are evaluated in order of priority.
Why this is correct
SD-WAN rules are evaluated in order of priority, meaning the rule with the lowest priority number (highest precedence) is inspected first and the first matching rule is applied exclusively. FortiGate processes rules top-down, and once a match is found, no subsequent SD-WAN rule is considered for that session, making priority sequencing critical for deterministic traffic steering.
- ✗
SD-WAN rules must use a 'load balancing' strategy.
Why it's wrong here
The 'load balancing' strategy is only one of several selectable strategies within an SD-WAN rule. Administrators can also choose 'manual' to pin traffic to a specific member, or 'best quality' to dynamically select the member with the best measured quality, so a load balancing strategy is not a mandatory requirement for every rule.
- ✓
SD-WAN rules can match based on application, destination, or source.
Why this is correct
SD-WAN rules support extensive match criteria including application (identified by FortiGuard's application control database), destination address, and source address. Additionally, criteria such as internet service, users, and port numbers can also be combined to create highly granular policies that steer specific traffic flows across the appropriate underlay links.
- ✗
Each SD-WAN rule can only contain one member.
Why it's wrong here
A single SD-WAN rule can contain multiple members, which are the physical or tunnel interfaces participating in the SD-WAN zone. The rule's strategy determines how these members are utilized, such as distributing sessions across several interfaces for load balancing or selecting the best-performing member based on health-check probes, so restricting rules to a single member would defeat the purpose of SD-WAN.
- ✓
If no SD-WAN rule matches, the traffic is processed by the implicit rule.
Why this is correct
When no explicit SD-WAN rule matches a session's characteristics, FortiGate falls back to the built-in implicit rule, which is always present with the lowest priority. This implicit rule uses the globally configured load balancing algorithm to select an SD-WAN member, ensuring that traffic is never dropped due to a missing match, while still allowing explicit rules to override behavior for specific flows.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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