Your organization has a Google Cloud Virtual Private Cloud (VPC) with subnets in us-east1, us- west4, and europe-west4 that use the default VPC configuration. Employees in a branch office in Europe…

While custom advertised routes can be configured, changing the VPC's dynamic routing mode to Global is a more comprehensive and efficient way to ensure all subnets are advertised without manually creating custom routes for each, especially when the VPC has a default configuration.

VPN connections are configured per VPN gateway and tunnel, not per subnet; this option misinterprets the role of VPN connectivity in relation to subnets.

By default, a Cloud Router in a VPC network with `Regional` dynamic routing mode only advertises routes to subnets in its own region; changing the VPC dynamic routing mode to `Global` allows the Cloud Router in `europe-west4` to advertise routes for all subnets across all regions (`us-east1`, `us-west4`, and `europe-west4`) to the on-premises branch office via HA VPN, ensuring full connectivity.

The `advertised routes` setting on a Cloud Router configures what specific routes are advertised, but the Cloud Router's ability to even *see* routes from other regions is controlled by the VPC network's overall dynamic routing mode. Setting advertised routes to Global wouldn't work if the VPC dynamic routing mode is still Regional.