So far you've learned about the default network, which is one of the three VPC network types in Google Cloud platform. Every project is provisioned with a default VPC network that comes with a preset of subnets and firewall rules. Specifically, a subnet is allocated for each region with a non-overlapping IP range and firewall rules that allows ingress traffic for ICMP, RDP, and SSH traffic from anywhere, as well as an ingress traffic from within the default network, for all protocols and ports. We recommend using the default VPC for prototyping and testing purposes rather than production workloads. In an auto mode network, one subnet from each region is automatically created. The default network is actually an auto mode network that you can manually add and have greater freedom to modify. These automatically created subnets use a set of predefined IP ranges with a /20 mask that can be expanded up to a /16. All of the subnets fits within the 10.128.0.0/9 cider block. Therefore, as the new GCP regions becomes available, new subnets in these regions are automatically added to an auto mode network using an IP range from that block. A custom mode network does not automatically create subnets. This type of network provides you with complete control over the subnets and the IP ranges. You decide which subnets to create in regions you choose, and using IP ranges you specify within the RFC 1918 address space. These IP ranges cannot overlap between subnets of the same network. This network is recommended for production because it assumes no implicit trust and gives you maximum control over its layout. It is also recommended network if you want to interconnect your VPC network with other networks, because you have control over the IP address layout. You can convert an auto mode network to a costume mode network to take advantage of the control that custom mode networks provide. However, this conversion is one way, meaning that custom mode networks cannot be changed to an auto mode networks. So carefully review the considerations of auto mode networks to help you decide which type of network meets your needs.
