If you are like me, you probably have had most of your networking setups with the typical and reliable Link Status for failure detection.
Link status is normally great, however, it does not detect misconfigured ports or switching failures.
Beacon Probing allows an ESX server to test links in a bond by sending a packet from one adapter to all of the other adapters within a Virtual Switch across the PHYSICAL LINKS. If a port is misconfigured or down, the probe will fail and ESX will detect the failure.
This probing can be used during initial installations to verify all links are correctly trunked or configured. In environments where you have your links going to multiple switches, this can also be useful to detect upstream failures in the path between physical NICs.