Which protocol is a vendor-neutral Layer 2 protocol that advertises a device's identity and capabilities to other network devices?

The correct response is focused on LLDP (Link Layer Discovery Protocol). LLDP is a vendor-neutral protocol that operates at Layer 2 of the OSI model, which allows network devices to advertise their identity and capabilities to other devices on the same local area network. This includes sharing information such as device type, software version, and capabilities, which helps in network management and topology discovery.

Being vendor-neutral, LLDP enables interoperability among devices from different manufacturers, unlike some proprietary protocols. This characteristic is particularly beneficial in complex networks where devices from various vendors need to work together smoothly.

Other protocols in the context provided serve different purposes or are specific to certain environments. For instance, CDP (Cisco Discovery Protocol) is a proprietary protocol used by Cisco devices, which limits its applicability to only Cisco networks. SNMP (Simple Network Management Protocol) is primarily used for network management and monitoring rather than advertising device identity. RTP (Real-time Transport Protocol) is used for delivering audio and video over IP networks, which is unrelated to device discovery.

Thus, LLDP stands out as the correct choice, being a standardized and widely applicable protocol for device identification and capability advertisement in diverse networking environments.