NSX backup fails with "Backup operation unknown error"

Products

• VMware NSX

Issue/Introduction

• Backup server is configured with fully qualified domain name.
• Scheduled backup will always fails with error "Backup operation unknown error":
  
• Manually created backup may be successfully created.
• In NSX Manager logs (this will be the node which is creating the backup), you may see the logs similar to samples below:
  var/log/syslog:
2025-07-18T09:00:00.399Z nsx.manager.example NSX 2255 - [nsx@6876 comp="nsx-manager" subcomp="node-mgmt" username="root" level="ERROR" errorCode="NOD110"] Error creating iptables rule,rc: 2, out: , err: iptables v1.8.7 (legacy): host/network `backup.server.example' not found#012Try `iptables -h' or 'iptables --help' for more information.
2025-07-18T09:00:00.401Z nsx.manager.example NSX 5212 SYSTEM [nsx@6876 comp="nsx-manager" errorCode="MP29256" level="ERROR" subcomp="manager"]
2025-07-18T09:00:00.401Z nsx.manager.example NSX 5212 SYSTEM [nsx@6876 comp="nsx-manager" errorCode="MP99" level="ERROR" subcomp="manager"] Unknown response code 36228
2025-07-18T09:00:00.401Z nsx.manager.example NSX 5212 SYSTEM [nsx@6876 comp="nsx-manager" errorCode="MP99" level="ERROR" subcomp="manager"] Cluster backup had error
2025-07-18T09:00:00.441Z nsx.manager.example NSX 5212 - [nsx@6876 comp="nsx-manager" errorCode="MP99" level="ERROR" s2comp="backup-restore" subcomp="manager"] Cluster backup failed with ; BackupAsyncStatus [BackupStatus [status=GENERIC_ERROR, statusDetail=Invalid file server specified., remoteUri=sftp://backup.server.example:22/cluster-node-backups, errorCode=null, startTime=1752829200193, endTime=1752829200401]; responseBody=null].

var/log/nvpapi/api_server.log 
2025-07-18T09:00:00.399Z napi.root.node.file-store.appliance_utils ERROR Error creating iptables rule,rc: 2, out: , err: iptables v1.8.7 (legacy): host/network `backup.server.example' not found
Try `iptables -h' or 'iptables --help' for more information.
• Forward name resolution of backup server's FQDN from the Manager running the backup doesn't resolve:
  dig backup.server.example

Environment

VMware NSX
VMware NSX-T Data Center

Cause

search-domain is not configured correctly, or is not configured at all on the impacted nodes. 

Resolution

Please review search-domain configuration on NSX Managers:

1. SSH to the Manager as admin
2. Confirm current configuration of search-domains:
   get search-domains
3. If needed, configure correct search-domain:
   set search-domains <new-search-domain>