Which two protocols are associated with the link layer of the TCP/IP reference model? (Choose two.)

UDP is a transport-layer protocol responsible for connectionless, end-to-end data delivery between hosts, operating two layers above the link layer.

LLDP (Link Layer Discovery Protocol, IEEE 802.1AB) operates at Layer 2 to advertise device identity and capabilities to directly connected neighbors, making it a link layer protocol in the TCP/IP model. Unlike higher-layer discovery mechanisms, LLDP frames are not routable and are confined to the local link segment.

STP (Spanning Tree Protocol, IEEE 802.1D) operates at Layer 2 to prevent switching loops by placing redundant ports in a blocking state, placing it at the TCP/IP link layer. STP uses Bridge Protocol Data Units (BPDUs) sent directly at Layer 2 without any IP header, confirming its operation exclusively at the link layer.

IPsec is a network-layer (Internet layer) protocol suite that provides authentication and encryption for IP packets, operating above the link layer.

HSRP is a Cisco first-hop redundancy protocol that operates at Layer 3 to provide default gateway failover, not at the link layer.