Quick Answer
The answer is a hash of source and destination IP addresses. ECMP load balancing on FortiGate distributes traffic by computing a hash from the source and destination IP fields in each packet, which ensures that all packets belonging to the same session follow the same path while different sessions are spread across the equal-cost routes. This hash-based approach is deterministic and avoids packet reordering, with the specific hash method—such as source-dest-ip or source-dest-port—controlled by the load-balance setting under the routing configuration. On the Fortinet NSE 7 Advanced Security NSE7 exam, this concept tests your understanding of how FortiGate’s ECMP algorithm selects paths without relying on round-robin or random distribution, and a common trap is assuming that traffic is split per-packet rather than per-session. Remember the memory tip: “IPs hash the path, ports are optional math”—the core hash always uses source and destination IPs, with port-based hashing only applied when explicitly configured.
This NSE7 practice question tests your understanding of advanced networking and sd-wan. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 multiple equal-cost routes to the same destination via two different interfaces. ECMP load balancing is enabled. What determines how traffic is distributed among the routes?
The interface speed
Why wrong: ECMP does not consider interface speed by default; it's per-flow hash.
A hash of source and destination IP addresses
Default ECMP uses source-dest-ip hashing.
Round-robin per packet
Why wrong: ECMP in FortiGate is per-session, not per-packet.
The route metric
Why wrong: Equal-cost means same metric; metric doesn't decide distribution.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
A hash of source and destination IP addresses
ECMP uses a hash algorithm based on source/destination IP and optionally ports to distribute sessions. The 'load-balance' setting in the routing configuration determines the method (e.g., source-dest-ip, source-dest-port).
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The interface speed
Why it's wrong here
ECMP does not consider interface speed by default; it's per-flow hash.
A hash of source and destination IP addresses
Why this is correct
Default ECMP uses source-dest-ip hashing.
Related concept
Static NAT maps one inside address to one outside address.
Round-robin per packet
Why it's wrong here
ECMP in FortiGate is per-session, not per-packet.
The route metric
Why it's wrong here
Equal-cost means same metric; metric doesn't decide distribution.
Common exam traps
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
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.
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
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
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.
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FAQ
Advanced Networking and SD-WAN — This question tests Advanced Networking and SD-WAN — Static NAT maps one inside address to one outside address..
The correct answer is: A hash of source and destination IP addresses — ECMP uses a hash algorithm based on source/destination IP and optionally ports to distribute sessions. The 'load-balance' setting in the routing configuration determines the method (e.g., source-dest-ip, source-dest-port).
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.
Static NAT maps one inside address to one outside address.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A FortiGate has two equal-cost paths to a destination network through two different ISPs. The administrator wants to load balance traffic across both links using ECMP, but notices that all traffic uses only one link. What should the administrator check first?
mediumWhy A: ECMP requires that routes have the same distance and priority. Additionally, FortiGate uses source-destination IP hash by default; if sessions are sticky, one link may carry all traffic.
Variation 2. A FortiGate has two equal-cost paths to a destination network. ECMP is enabled. The administrator notices that all traffic uses the first path. What is the most likely cause?
hardWhy C: ECMP distributes session flows, but if all traffic is using one path, it might be due to a session-based hash that results in the same path for all sessions, or the ECMP load balancing may be set to 'source-dest-ip' and the traffic is from one source to one destination. More likely, the ECMP load balancing mode is set to 'usage' or there is a policy-based route overriding.
Last reviewed: Jun 21, 2026
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