Beacon probing is a network failover detection mechanism that sends and listens for beacon probe packets on all physical NICs in the team. In a teamed uplink packets will be sent through each physical NIC.

 

Beacon probing detects failures, such as cable disconnects and physical switch power failures on the physical network. It uses this packet information along with link state to determine link failure. The design of Beacon probing works with physical Switch redundant networking to determine downstream link failures beyond the ESXi host networking. The following is required for beacon probing:

• 3 or more physical NICs in the team connected to 3 separate physical switches.
• VMware does not recommend multiple physical NIC connections to the same physical Switch. This can cause Beacon probing to fail to detect issues beyond the switch.

For example:
 

 

 

 

In the above example, all the physical NICs have a discrete path to the distributed switch. When the failure happens at a distribution switch level, beacon probing will detect this failure due to the uplink on the ESXi host that connects to the failed distributed switch will not receive the beacon probe packets.

 

Below are the configurations which are NOT Recommended:

Configuration 1:

 

Configuration 2:


Note: Since Beacon probing intends and design for network redundancy to detect network failover for teaming, each pNICs in a team send out and receive Beacon probe packet to make sure that the connections/Links are working fine. Thus, it is required to have 3 or more pNICs to prevent split brain condition and works more accurate network failure detection. However, we do not recommend multiple pNICs connect to the same pSwitch. It is because once Beacon probing detects the failure at distribution switch, the Beacon probe packets can transmit in the pSwitch. So it is meaningless to have Beacon probing in this situation. Please see the not recommended layout with multiple pNICs and pSwitches as example.
 

When should you enable beacon probing?
You must enable beacon probing when downstream link failures may impact availability and there is no Link State Tracking on the physical switch.

For more information, see:

 

Beacon probing utilizes virtual MAC addresses to check the link status of each VLAN and determine link failure for physical NICs in a vSwitch team. You may see entries for virtual MAC address in the esx.conf file and the MAC address table of your physical switch. For more information, see:

• VMware vSphere Blog - Beaconing Demystified: Using Beaconing to Detect Link Failures
• VMware SMB Blog - Back To Basics: Configuring Standard vSwitch (Part Two of Three)
• Beacon packets are sent even if the vSwitch is not configured to use Beacon Probing for Network Failover Detection (1024435)