Troubleshooting MAC Address Flapping Errors with ESXi Hosts

Products

• VMware vSphere ESXi

Issue/Introduction

• Network switch reports MAC address flapping errors similar to:
   
  %SW_MATM-4-MACFLAP_NOTIF: Host aaaa.bbbb.cccc in vlan 123 is flapping between port Gi3/0/24 and port Gi2/0/18
• The issue occurs with specific MAC addresses (including both VM MAC addresses and physical NIC MAC addresses) flapping between different switch ports connected to the same ESXi host.
• This issue may cause network connectivity issues or may just be cosmetically in logs on the switchports connected to the ESXi host
• The following symptoms can be observed in the network switch logs:
  • MAC addresses are detected on two different switch ports
  • MAC flapping notifications appear in rapid succession
  • The affected MAC addresses are typically those shared between vmk0 management interface and physical NICs (vmnics), which is a normal behavior that becomes problematic when using unsupported Beacon Probing configurations
• This issue involves the vmk0 management interface sharing the same MAC address as a physical NIC or storage adapter, which becomes problematic with certain teaming configurations.

 

Environment

• VMware vSphere ESXi 7.x
• VMware vSphere ESXi 8.x
• vSwitch configuration with active/active uplinks
• Network adapters configured with Beacon Probing enabled

Cause

This issue occurs due to using Beacon Probing in an unsupported network configuration:

1. Beacon Probing is a network failover detection mechanism that requires specific network topology requirements to function properly.
2. The vmk0 management interface shares the same MAC address with a physical network interface (vmnic) or storage adapter, which becomes problematic when using unsupported Beacon Probing configurations.
3. When Beacon Probing is used without meeting the minimum topology requirements, it can cause the same MAC address to appear on multiple switch ports, triggering the switch's MAC flapping protection.

Resolution

Supported vs. Unsupported Beacon Probing Configurations

The key point to understand is that when Beacon Probing is implemented in unsupported configurations (such as with fewer than 3 NICs or with multiple NICs connected to the same switch), MAC address flapping can occur because:

1. The vmk0 management interface shares its MAC address with a physical NIC
2. In unsupported configurations, beacon probe packets may appear on multiple switch ports
3. This combination causes the switch to detect the same MAC address on different ports, triggering MAC flapping errors

Additional Information

• For detailed information on proper Beacon Probing implementation requirements, see What is beacon probing?
• For specific resolution steps to address MAC flapping with Beacon Probing, see VMware ESXi host network flapping error when Beacon Probing is selected
• For information on vmk0 sharing MAC addresses with physical NICs, see vmk0 management network MAC address is not updated when NIC card is replaced or vmkernel has duplicate MAC address

When Beacon Probing is required for enhanced failure detection but the current network topology does not support it, consider implementing one of these alternatives:

1. Reconfigure the physical network to meet Beacon Probing requirements (3+ NICs to 3+ separate switches)
2. Implement Link State Tracking on the physical switches as an alternative to Beacon Probing
3. Use EtherChannel/LACP with IP hash load balancing for proper redundancy and performance

If the error persists after implementing a supported configuration, contact Broadcom Support for further assistance.

Please provide the following information when opening a support request with Broadcom for this issue:

• Network configuration details (screenshots of vSwitch configuration)
• MAC addresses involved in the flapping
• Switch ports configuration and logs showing the MAC flapping errors
• ESXi host logs, particularly those showing the networking configuration