A company uses Transit Gateway Connect and two SD-WAN virtual appliances to extend its SD-WAN to AWS. Company policy dictates that only one SD-WAN appliance should carry AWS-bound workload traffic at a time. How should routing be configured so only the primary appliance is preferred?

The ASPATH prepend attribute is a standard BGP mechanism to influence route selection. By prepending the Autonomous System (AS) number multiple times on routes advertised by the secondary SD-WAN appliance, its ASPATH length becomes longer. BGP prefers routes with a shorter ASPATH, thus making the primary appliance's routes more desirable to the Transit Gateway. This ensures that the Transit Gateway directs traffic to the primary appliance as long as it's available. Adding a static default route to the secondary appliance and more specific routes to the primary would create a complex and potentially conflicting routing setup. Configuring a BGP community tag 7224:7300 is used for Transit Gateway route propagation control, not for influencing path preference. Disabling ECMP would prevent load balancing but wouldn't inherently prioritize one appliance over another if both are advertising equally preferred routes.