ESXi host logs flooding with "rn_addmask bcmp" messages

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:
• ESXi host status appears as "Not Responding" in vCenter.
• vmkernel.log is flooded with the following warning message: Tcpip_Vmk: 123: rn_addmask bcmp(addmask_key=..., x->rn_key=..., mlen=0x8) != 0
• Management services (hostd, vpxa) may fail to communicate with vCenter due to the inability to process network routes.

Cause

Inconclusive - These log entries indicate that the ESXi network stack is struggling to resolve or process active routes or network traffic. While this can sometimes be caused by invalid VMkernel interface configuration, in transient cases, this is triggered by external network conditions such as an ARP/broadcast storm or network loops upstream of the ESXi host. The host is not technically failing; it is simply overwhelmed by the volume of packets flooding its routing table.

Resolution

1. Host Recovery: Restart the hostd and vpxa services on the host (/etc/init.d/hostd restart | /etc/init.d/vpxa restart). Then, reconnect the host to the vCenter by right clicking on the hosts, select connection, click reconnect.

2. If restarting services and reconnecting the host does not work, perform a reboot of the affected ESXi host. This clears the network stack's current state and allows the host to re-establish normal communication once the external network traffic has stabilized.

3. Environment Monitoring: If the issue resolves after a reboot without any configuration changes, treat this as a transient environmental network condition.

4. Physical Infrastructure Investigation: If the log flooding persists or recurs, inspect the upstream physical network infrastructure for:
• Duplicate IP addresses on the same subnet.
• Physical switches configured with broadcast storm control that may be dropping traffic unexpectedly.
• Network loops on the upstream segment.
Note: If the flooding continues immediately after a reboot or persists despite a stable upstream network, open a case with Broadcom Support.