Which protocol is responsible for sending periodic advertisements to learn device information in Cisco networks?

The correct choice is the protocol that facilitates the exchange of information between directly connected Cisco devices, specifically Cisco Discovery Protocol (CDP). CDP operates at the Data Link Layer and is used primarily in Cisco environments to gather information about neighboring devices such as their device type, IP address, and capabilities. By sending periodic advertisements, CDP enables devices to discover relevant details automatically without manual configuration.

This automatic discovery process helps network administrators gain visibility into the network topology and quickly troubleshoot connectivity issues. As devices periodically send CDP advertisements, they maintain updated information about themselves and their surroundings, creating a dynamic view of the network.

In contrast, the other protocols mentioned serve different purposes. Link Layer Discovery Protocol (LLDP) is a vendor-neutral protocol similar to CDP but is not specific to Cisco devices. Spanning Tree Protocol (STP) is used for preventing loops in network topologies, and Point-to-Point Protocol (PPP) is primarily used for establishing direct connections between two nodes in point-to-point links. These protocols do not focus on advertisement and discovery of device information like CDP does.