Which of the following best describes how UDLD operates?

UDLD, or Unidirectional Link Detection, operates by sending hello messages that must be echoed back to the originating device. This is a critical function as it ensures that both ends of a link are operational and can communicate bidirectionally. If one side of the link is unable to send or receive data properly, UDLD will notice that the expected echo reply is not received. In this situation, UDLD will take action, such as disabling the interface or alerting an administrator, to prevent potential issues like loops or miscommunication in the network.

This mechanism is essential in environments where unidirectional failures are a possibility, as these failures can lead to network loops and other connectivity issues. By relying on echo replies from the far end of a link, UDLD provides a robust way to detect and prevent problems associated with links that only appear active but may be failing to send or receive data properly.