You must enable dynamic routing mode on the external VPC of the newly created NCC setup. This ensures that the cloud router dynamically advertises subnets and propagates learned routes in the region where the router is configured or throughout the entire VPC network.
- In the GCP management console, go to Networking > VPC Network > (external_vpc_name) > EDIT.
- Under Dynamic routing mode, select Global.
- Click SAVE.
- Go to the external subnet's ROUTES tab. You should see the new dynamic routes.