Create a hierarchical firewall policy configured at the organization to deny all connections from 0.0.0.0/0.

Create a hierarchical firewall policy configured at the organization to allow connections only from internal IP ranges.

Create a Google Cloud Armor security policy to deny traffic from 0.0.0.0/0.

Create a firewall rule for each virtual private cloud (VPC) to deny traffic from 0.0.0.0/0 with priority 0.