Which protocol is defined by IEEE 802.1AX that coordinates communications between two hosts?

• A. Link Aggregation Control Protocol (LACP)
• B. Spanning Tree Protocol (STP)
• C. Border Gateway Protocol (BGP)
• D. Internet Control Message Protocol (ICMP)

Answer: (A)

The concept being tested is how multiple physical links can be combined to act as a single, higher-bandwidth channel. This is achieved by a protocol that coordinates the endpoints to form a Link Aggregation Group. IEEE 802.1AX defines this protocol as the one that negotiates which physical links become part of the same logical link, exchanges partner information, and maintains the active set of links through periodic messages. This coordination lets two devices treat several cables as one path, with traffic distributed across the active links and automatic reconfiguration if a link fails or a new one is added, improving both bandwidth and resilience. The other options don’t perform this function: a protocol focused on preventing loops in a switched network, a routing protocol between networks, or a protocol for diagnostic messages cannot create and manage a shared, aggregated link between endpoints. Therefore, the protocol defined by IEEE 802.1AX that coordinates communications between two endpoints is the one used for link aggregation.