General Availability: You can use the Resolve subnet mask setting on a subnet to configure all attached Compute Engine...

General Availability: You can use the Resolve subnet mask setting on a subnet to configure all attached Compute Engine instances with the same netmask as the subnet (instead of /32). Configuring larger instance netmasks lets compute instances discover the MAC addresses of other machines within the same subnet and directly communicate with them by using destination MAC addresses.

For more information, see Compute instance netmasks.