Cloud DNS private zones offers flexibility in your configurations by allowing multiple zones to be attached to a single VPC network. Additionally, support for split horizons allows you to have a private zone share the same name as a public zone while resolving to different IP addresses in each zone.
DNS peering allows one network to forward DNS requests to another network
When GCP networks are peered, they do not automatically share private DNS zones, DNS policies, or even internal DNS records. Cloud DNS peering, currently in beta, provides a second method for sharing DNS data. You can configure all or a portion of the DNS namespace to be sent from one VPC to another and, once there, it will respect the DNS policies or matching zones defined in the peered network.