DVS switch health alarm shows an error stating "Not all VLAN MTU settings on the external physical switch allow the vSphere Distributed Switch maximum MTU size packets to pass on the uplink port XXX in vSphere Distributed Switch"

Products

• VMware vSphere ESXi

Issue/Introduction

• On the ESXi host, there is an alarm stating an error as shown below

"Not all the configured VLANs in the vSphere Distributed Switch were trunked by the physical switch connected to uplink port 447 in vSphere Distributed Switch on host"

• Login to the ESXi host as user root. In /var/run/log/hostd.log, there are errors related to the VLAN settings.

2025-06-03T17:09:34.301Z In(166) Hostd[######]: [Originator@6876 sub=Vimsvc.ha-eventmgr] Event 3306 : Not all the configured VLANs in the vSphere Distributed Switch were trunked by the physical switch connected to uplink port ### in vSphere Distributed Switch on host <ESXi FQDN>.
2025-06-03T17:09:34.301Z In(166) Hostd[######]: [Originator@6876 sub=Vimsvc.ha-eventmgr] Event 3308 : Not all the configured VLANs in the vSphere Distributed Switch were trunked by the physical switch connected to uplink port ### in vSphere Distributed Switch on host <ESXi FQDN>.

Environment

vSphere ESXi 

Cause

This issue is caused by a configuration mismatch where the VLAN is assigned to the vSwitch but is not permitted (or trunked) on the connected physical switch port.

 

Resolution

Need to thoroughly verify and validate with the physical network team to ensure the physical switch is configured to trunk the corresponding VLAN

Additional Information

• From the alarm screenshot and the error message in /var/run/log/hostd.log, note down the port number for which the alarm is triggered.
• Login to the host as user root and run the command net-dvs -l, search for the appropriate port number listed in the error message/alarm and verify whether there are any untrunked VLAN listed as shown below
• From the output below, the following port xxx show that VLAN 0,115 is trunked. But, VLAN 421 is not trunked.
  
  

  net-dvs -l
  
  port xxx:
  Trunked VLAN: 0,115
  Untrunked VLAN:421

• In this case, a portgroup configured with VLAN A exists on the virtual switch, and it is carrying traffic from VMs or VMkernel ports on VLAN A. VLAN A is not allowed (or trunked) on the connected physical switch port, this VLAN mismatch leads to the triggered alarm

To know more about VLAN settings, refer to the KB VLAN configuration on virtual switches, physical switches, and virtual machines