NSE4 High Availability and Diagnostics Practice Question
In a FortiGate HA cluster, the administrator needs to perform a firmware upgrade without causing a full service outage. Which procedure should be followed?
⚠ Common exam trap
NSE4 often tests the order of HA firmware upgrades — candidates incorrectly assume upgrading the primary first is fine because it 'leads' the cluster, missing that it causes an outage.
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
✓
Upgrade the secondary unit first, then perform a failover, then upgrade the primary unit
In a FortiGate HA cluster, the correct upgrade procedure is to upgrade the secondary (subordinate) unit first, then trigger a failover so it becomes primary, then upgrade the former primary. This maintains service continuity because at least one unit is always running the stable firmware and passing traffic. Upgrading the primary first would cause an outage during the upgrade window.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Upgrade the primary unit first, then the secondary unit
Why it's wrong here
Upgrading the primary unit first immediately triggers a failover to the secondary, but because the secondary is still running the previous FortiOS version, the HA cluster now operates in a transient mixed-firmware state that FortiOS does not support. If the primary's upgrade succeeds and it rejoins, the cluster will have two units on different builds, which can lead to synchronization errors, compatibility issues, and degraded failover behavior. This sequence also risks an immediate session loss if the failover occurs before the primary is properly prepared.
- ✓
Upgrade the secondary unit first, then perform a failover, then upgrade the primary unit
Why this is correct
The correct procedure is to upgrade the standby unit first, verify it has booted and joined the cluster with a healthy synchronization, then manually fail over so that the upgraded unit becomes primary and handles traffic. After that, upgrade the former primary (now standby) to the same version, ensuring both units finally run identical firmware. This rolling upgrade preserves a live unit for every step, avoiding an outage and keeping the HA pair in a supported configuration throughout.
- ✗
Disable HA and upgrade each unit separately
Why it's wrong here
Disabling HA before upgrading removes all redundant protection, so if a hardware failure or reboot occurs during the upgrade, the network loses forwarding capability entirely. Additionally, disabling HA likely erases or invalidates the cluster membership and synchronization state; after separate upgrades you must re-establish the cluster, which may require a reboot of both units and re-synchronization of configurations from scratch. This approach creates a maintenance window that a well-designed HA upgrade should eliminate.
- ✗
Upgrade both units simultaneously
Why it's wrong here
Upgrading both units at the same time intentionally creates a full outage because both FortiGates will reboot into the upgrade process simultaneously, leaving no unit to carry traffic. If one unit fails mid-upgrade or the two units complete at slightly different times, the HA pair may come up with mismatched firmware and fail to re-form as a cluster, or one unit may keep wrestling for primary status. This method also eliminates any ability to verify the first unit's upgrade before moving to the second, undermining confidence in the process.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Fortinet exam blueprint
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.