Which two statements about equal-cost multi-path (ECMP) configuration on FortiGate are true? (Choose two.)

Statement A is correct because when SD-WAN is disabled, FortiGate uses a global setting for the ECMP load-balancing algorithm. This is configured using the v4-ecmp-mode parameter. One of the available modes is usage-based, which the official FortiOS Administration Guide explicitly refers to as "also known as volume-based." This algorithm distributes traffic based on bandwidth utilization.

Statement D is correct because when SD-WAN is enabled, it overrides the global ECMP settings for traffic matching an SD-WAN rule. The load-balancing algorithm for SD-WAN traffic is configured within each specific SD-WAN rule (service) using the load-balance-mode parameter, allowing for granular control.

B: ECMP stands for Equal-Cost Multi-Path. By definition, all routes in an ECMP set must have identical administrative distance and metric (cost). SD-WAN can use unequal cost paths, but this is not ECMP.

C: This statement is incomplete and therefore misleading. While the ECMP algorithm mode is selected in config system settings, fully configuring certain modes like weight-based or usage-based requires additional configuration elsewhere (e.g., on static routes or interfaces).

1. FortiOS Administration Guide 7.6.1

Chapter "Routing"

Section "ECMP load balancing methods"

p. 1010.

This section states for the usage-based method: "Also known as volume-based

this method directs new sessions to the interface with the most available bandwidth." This directly supports statement A.

2. FortiOS SD-WAN Architecture Guide 7.6

Section "SD-WAN rules"

Subsection "Load balancing algorithms"

p. 21.

This section details the load balancing algorithms for SD-WAN rules

stating they are "configured in SD-WAN rules" and shows the parameter is load-balance-mode. This directly supports statement D.

3. FortiOS SD-WAN Architecture Guide 7.6

Section "Routing"

Subsection "ECMP"

p. 38.

This section defines ECMP: "ECMP allows the router to load balance traffic over multiple links that have the same destination

administrative distance

and metric." This directly refutes statement B.

4. FortiOS CLI Reference 7.6.1

config system settings and config system sdwan sections.

The reference confirms that v4-ecmp-mode is the parameter under config system settings for global ECMP and that load-balance-mode is the parameter under config system sdwan -> config service for SD-WAN rules. This supports the context for statements A

C

and D.