Which feature ensures that only one active EtherChannel exists between two switches?

The Link Aggregation Control Protocol (LACP) is the feature that ensures only one active EtherChannel exists between two switches. It works by enabling the aggregation of multiple physical links into a single logical channel, effectively increasing bandwidth and providing fault tolerance.

LACP helps to prevent loops in the network by collaborating with the Spanning Tree Protocol (STP), which is responsible for loop prevention in Ethernet networks. While STP and Rapid STP manage the overall topology and can block redundant links, it is LACP that specifically governs the negotiation and establishment of link aggregation. If more than one EtherChannel is configured between the same two switches, LACP ensures that only one remains active by dynamically enabling or disabling the links based on their availability and status.

This makes LACP a critical component in maintaining efficient network performance, as it helps to avoid confusion and inefficiencies that could arise from having multiple active channels between the same devices. In contrast, the Spanning Tree Protocol and Rapid Spanning Tree Protocol focus more on managing the overall topology rather than the specifics of link aggregation, and Port Aggregation Protocol is an older, less commonly used protocol compared to LACP.