How does Cloud Router behave when operating on a VPC with auto subnet mode?

When a Cloud Router is operating in a VPC with auto subnet mode, it automatically advertises the region's /20 prefix. This is a key feature of Cloud Router, as it enables dynamic routing by automatically managing the routes for the subnets created in your VPC.

In auto subnet mode, Google Cloud creates subnets by allocating a portion of the available IP address space in the region, which typically uses a /20 CIDR block. The Cloud Router then takes these prefixes and advertises them to other routers, such as on-premises networks or other VPCs connected via VPN or Interconnect. This feature allows seamless integration and communication between different network segments while dynamically adapting to changes in the VPC, such as when additional subnets are created or removed.

The other options do not align with how Cloud Router behaves in this context. Advertising a custom subnet, for example, is relevant in scenarios where specific subnets are defined rather than in auto mode, where the behavior is more standardized. Blocking all incoming traffic and disabling dynamic routing are not characteristics relevant to the function of Cloud Router in this scenario. The focus of Cloud Router in auto subnet mode is on automatically managing and advertising network prefixes to ensure effective routing.