What does a switch configured to dynamic auto do if it receives a DTP frame?

A switch configured to dynamic auto will respond to a Dynamic Trunking Protocol (DTP) frame. When the dynamic auto mode is set on a switch port, it has the potential to become a trunk port if the connected device sends a DTP frame and indicates that it is willing to form a trunk.

In this scenario, the switch in dynamic auto mode effectively listens for the DTP frames from the other device. If it receives such a frame and the other device is set to create a trunk (like a switch configured as dynamic desirable), the switch will respond and configure its port as a trunk link. This ability to respond allows for a dynamic negotiation of trunking, making the configuration process easier and reducing the potential for misconfigurations in the network.

The other options do not accurately describe the behavior of a switch in dynamic auto mode when it interacts with DTP frames. The ability to initiate a response rather than ignore frames or set the port to access mode is what allows this negotiation process to occur.