The regional private internal IP address that is used to establish
BGP sessions to a VM instance acting as a third-party
Router Appliance, such as a Next Gen Firewall, a Virtual Router, or
an SD-WAN VM.
The URI of the subnetwork resource that this interface belongs to, which
must be in the same region as the Cloud Router.
When you establish a BGP session to a VM instance using this interface,
the VM instance must belong to the same subnetwork as the subnetwork
specified here.