CDP is primarily used to display information about which of the following?

CDP, or Cisco Discovery Protocol, is primarily used to display information about directly connected Cisco devices. This network protocol enables Cisco devices to share information about themselves with other directly connected Cisco devices, such as device identifiers, IP addresses, and operating system versions. By using CDP, network administrators can easily discover and monitor the devices in their local network, which is essential for effective network management.

The information shared by CDP can help in troubleshooting connectivity issues, understanding the network topology, and facilitating the configuration of network devices. CDP operates at Layer 2 of the OSI model, allowing it to gather and disseminate information about the physical connections in a Cisco environment.

The other choices pertain to different functionalities not encompassed by CDP. For instance, routing tables are related to the data that routers use to forward packets, but that information is learned through routing protocols rather than CDP. Similarly, performance metrics for WAN modules and ISDN connectivity statuses involve specific technologies or protocols that are outside the scope of what CDP is designed to accomplish. Therefore, the use of CDP focuses exclusively on the direct relationships and configurations among Cisco devices within the same local area network.