The answer is to enable the 'session-based' algorithm under ECMP load balancing settings. This is correct because ECMP load balancing by default uses a source-destination IP hash, which can cause packets from the same TCP session to traverse different WAN links if the hash changes mid-flow, breaking session persistence. The session-based algorithm overrides this by hashing on the entire 5-tuple (source IP, destination IP, protocol, source port, destination port) and maintaining a consistent egress interface for all packets of a given session, ensuring stateful firewall inspection and TCP sequence integrity. On the Fortinet NSE 7 Advanced Security exam, this question tests your understanding of how ECMP interacts with session state in a multi-WAN scenario—a common trap is confusing 'source-IP-based' or 'weighted' load balancing with session persistence. Remember the mnemonic: "Session-based sticks the session; hash-based hacks the path."
NSE7 Advanced Networking and SD-WAN Practice Question
This NSE7 practice question tests your understanding of advanced networking and sd-wan. 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 FortiGate has two WAN links and uses ECMP load balancing for default routes. The administrator wants to ensure that all packets belonging to the same TCP session go out the same interface. Which setting should be enabled?
Why wrong: Persistent NAT is for source NAT stickiness, not for routing symmetry.
B
ECMP source-destination-ip hash
Why wrong: Source-destination-ip hash uses IP addresses, not TCP session, so different ports may cause different paths.
C
ECMP with source-ip hash
Why wrong: Source-ip hash uses only source IP, but still does not guarantee per-session stickiness if multiple sessions from same source IP with different dest IPs.
D
ECMP with 'session-based' algorithm
Session-based ECMP uses a hash of the 5-tuple (src IP, dst IP, protocol, src port, dst port) to ensure all packets of a session use the same interface.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ECMP with 'session-based' algorithm
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Persistent NAT
Why it's wrong here
Persistent NAT is for source NAT stickiness, not for routing symmetry.
✗
ECMP source-destination-ip hash
Why it's wrong here
Source-destination-ip hash uses IP addresses, not TCP session, so different ports may cause different paths.
✗
ECMP with source-ip hash
Why it's wrong here
Source-ip hash uses only source IP, but still does not guarantee per-session stickiness if multiple sessions from same source IP with different dest IPs.
✓
ECMP with 'session-based' algorithm
Why this is correct
Session-based ECMP uses a hash of the 5-tuple (src IP, dst IP, protocol, src port, dst port) to ensure all packets of a session use the same interface.
Related concept
Static NAT maps one inside address to one outside address.
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 NSE7 NAT questions on configuration and troubleshooting.
Advanced Networking and SD-WAN — This question tests Advanced Networking and SD-WAN — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: ECMP with 'session-based' algorithm
What should I do if I get this NSE7 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 NSE7 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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