While troubleshooting a network connectivity problem, a technician observes steady link lights on both the workstation NIC and the switch port to which the workstation is connected. However, when the ping command is issued from the workstation, the output message "Request timed out." is displayed. At which layer of the OSI model does the problem most likely exist（）。

• A、the session layer
• B、the protocol layer
• C、the data link layer
• D、the access layer
• E、the network layer
• F、the application layer