NSE7 Advanced Networking and SD-WAN Practice Question
A FortiGate is configured with SD-WAN using load balancing algorithm 'source-dest-ip'. What is the primary characteristic of this algorithm?
⚠ Common exam trap
Many exam-takers confuse 'source-dest-ip' with 'round-robin' or 'bandwidth-based' algorithms, assuming it distributes traffic evenly, when in fact it prioritizes per-flow stickiness over 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
✓
All traffic from the same source IP to the same destination IP uses the same SD-WAN member.
The 'source-dest-ip' load balancing algorithm in SD-WAN uses a hash of both the source IP and destination IP to deterministically select an SD-WAN member. This ensures that all packets belonging to the same flow (same source-destination pair) are consistently forwarded over the same member, preserving per-flow stickiness and avoiding out-of-order delivery.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Traffic is sent to the member with the highest bandwidth.
Why it's wrong here
No SD-WAN algorithm uses bandwidth as the sole criterion.
- ✗
Traffic is sent to the member with the lowest cost metric.
Why it's wrong here
Lowest-cost is a different algorithm that uses cost values assigned to members.
- ✗
Traffic is distributed evenly across all SD-WAN members regardless of source or destination.
Why it's wrong here
That describes 'volume' or 'session' algorithms, not source-dest-ip.
- ✓
All traffic from the same source IP to the same destination IP uses the same SD-WAN member.
Why this is correct
Source-dest-ip hashing ensures that traffic belonging to the same source-destination pair is consistently sent over the same link, preserving session affinity.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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