File Server Health alert: DNS forward and reverse lookup are not working or incorrect.

Products

• VMware vSAN

Issue/Introduction

• In vSAN Skyline Health, the File Server Health will appear in red with below errors:

vCenter UI>vSAN Cluster>Monitor>Skyline health

• The above messages are also seen in  /var/run/log/vsanfs.mgmt.log:

2025-10-09T09:35:40.822Z In(14) vsand[2103948]: [opID=#####-### VsanFileServiceSystemImpl::_QueryFileServerHealth] Append container health: (vim.host.VsanFileServerHealthSummary) {
2025-10-09T09:35:40.822Z In(14)[+] vsand[2103948]:   domainName = '***.com',
2025-10-09T09:35:40.822Z In(14)[+] vsand[2103948]:   fileServerIp = '##.##.##.##',
2025-10-09T09:35:40.822Z In(14)[+] vsand[2103948]:   nfsdHealth = 'green',
2025-10-09T09:35:40.822Z In(14)[+] vsand[2103948]:   networkHealth = 'green',
2025-10-09T09:35:40.822Z In(14)[+] vsand[2103948]:   rootfsHealth = 'green',
2025-10-09T09:35:40.822Z In(14)[+] vsand[2103948]:   description = 'File server runtime is in good state.\nBoth DNS forward and reverse lookup are not working or incorrect.',

• Reviewing the logs in /var/run/log/vsanfs.mgmt.log, you may see entries similar to:

2025-10-09T09:40:59.157Z Wa(12) vsanfs.mgmt[2103701]: [2103862] [VDFSEndpointMonitorContainer::_CheckContainerHealthItem] CONT: Error running DnsLookupTest on container File server node IP "##.##.##.##": dnsbothlookuperror, Forward lookup output:;; communications error to DNS server IP#53: host unreachable

• vSAN File Service VMs in the cluster cannot ping each other.

Environment

VMware VSAN 8.x

Cause

This indicates a network connectivity issue, where the vSANFS VM is unable to reach the DNS server or communicate with peer vSANFS VMs.

Resolution

1. Validate Uplinks
   1. Navigate to the affected vCenter Port Group
   2. Confirm that the correct uplinks are assigned
   3. Go to Configure > Policies
2. Verify VLAN Configuration
   1. Ensure that the correct VLAN tags are applied in the same port group configuration.
3. Verify VM network interface connectivity
   1. Check that the vSAN File Service VM(s) has its network interface in a connected state.
4. Engage Network team or vendor to further investigate the issue.