The route-tag setting in a FortiGate SD-WAN rule serves as a dynamic destination matching criterion. It allows the rule to match traffic destined for prefixes that have been assigned a specific numerical tag. These tags are typically applied to routes learned through dynamic routing protocols, such as BGP or OSPF, using route maps. This mechanism enables the SD-WAN to steer traffic based on dynamically learned network information without requiring manual updates to the destination addresses within the SD-WAN rules. For instance, all routes learned from a specific data center can be tagged, and a rule can use that tag to direct all traffic for those destinations over a preferred link.

A. Health check probes are configured on a per-member basis within the SD-WAN settings to monitor link quality, not selected via route tags in traffic rules.

C. This statement is too general. The route-tag is a specific filter for the destination of a traffic flow, not a broad indicator of all possible routes.

D. The route-tag is used to identify the destination of the traffic, not to select the outgoing SD-WAN members (interfaces) that will carry the traffic.

1. FortiOS 7.0.0 Administration Guide: In the "SD-WAN" chapter, section "SD-WAN rules", it states, "Route tags can be used to match a route that has been learned through BGP or OSPF... The route tag is used as the destination for the SD-WAN rule." (p. 1238).

2. FortiOS CLI Reference 7.0.0: Under config router sdwan, config rule, the command set route-tag is described with the helper text: "Use route-tag to match output of dynamic routing protocol." This confirms its use for matching dynamically learned routes.

3. Fortinet Certified Professional - Network Security 7.2 Study Guide: The "SD-WAN" chapter explains, "SD-WAN rules can use route tags to match destinations. You can configure BGP and OSPF to add route tags to the routes they advertise and learn. This way, you can dynamically populate the destinations in the SD-WAN rules routing table." (p. 315).