Troubleshooting Network Loops with Virtual Appliances (Aruba VMs) in Promiscuous Mode (vSphere)

Products

• VMware vSphere ESXi

Issue/Introduction

When deploying virtual appliances (such as Aruba Wireless Controllers) in an HA pair on vSphere, you may experience intermittent 50% packet loss, high management latency, and CPU spikes (up to 80% utilization on the stm process). These issues often occur when one VM is promoted to Primary.

Environment

VMware vSphere ESXi 8.x

VMware vCenter Server 8.x

Aruba VMs 8.10

Cause

The issue is a network reflection loop (In-Guest Promiscuous Reflection) caused by deploying additional, newly provisioned virtual appliances into a wide-open, multi-VLAN global trunk group (DPortGroup-Trunked-ALL) while having Promiscuous Mode set to Accept.

Technical Breakdown:

• The Promiscuous Ingest: With Promiscuous Mode set to "Accept" on the broad global trunk port group, the newly deployed VMs (distinct from the primary/secondary HA pair) simultaneously ingest background multicast frames (such as VRRP).
• The In-Guest Reflection: These newly deployed VMs swallow these frames and echo-reflect them through their secondary interfaces into unbundled physical switch ports.
• The MAC Table Collapse: The physical switch ports (operating as standalone trunks) receive identical MAC frames across separate ports. This causes the MAC address table to flap instantly, corrupting the table.
• Packet Loss & CPU Spike: The switch table corruption causes return traffic to split, forcing 50% of traffic down the standby link where ESXi drops it (UplinkRcvKernel drop). The HA pair, hit by constant path transitions, spikes CPU usage as it struggles to process the flood.

Resolution

1. Restrict Port Group Assignment: Move all virtual appliances (including new deployments) out of global trunk groups. Assign them to dedicated, specific port groups with strictly defined VLANs.
2. Bundle Physical Ports: Ensure physical switch ports connected to virtual appliances are bundled into LACP port-channels (e.g., ae interfaces) rather than operating as independent standalone trunks.
3. Validate via Tracing:
   • ESXi: Use pktcap-uw --uplink [vmnic] -o [file] to check for UplinkRcvKernel (Inbound Receive) drops.
   • Physical Switch: Check switch logs for duplicate VRRP multicast frames entering standalone ports with an "In" (Inbound) tag.
4. Review Security Policy: While Promiscuous Mode may be required for specific appliance features, ensure it is enabled only on the specific, isolated port group—never at the global vSwitch level.