NSX Backup fails with error "Either backup server login failed or unauthorized access to backup directory"

Products

• VMware NSX

Issue/Introduction

• Last Backup Status showing "Failed" while Node & Cluster backups shows "Successful".

• Pinging the SFTP server from the NSX Manager succeeds, but connecting to the SFTP server over port 22 fails.
  • NSXMgr> nc -zv <SFTP server IP address> 22
• In /var/log/syslog errors similar to the below are observed:

YYYY-MM-DDT14:11:28.457Z <NSX_MGR_FQDN> NSX 77753 - [nsx@6876 comp="nsx-manager" errorCode="MP29115" level="ERROR" s2comp="backup-restore" subcomp="manager"] Cluster backup failed with ; BackupAsyncStatus [BackupStatus [status=AUTH_FAILURE, statusDetail=Cannot connect to sftp server. The remote server returned error: status: 255   out: '[Errno 5] Input/output error'., remoteUri=sftp://<SFTP_Server>:22/<Backup_Directory>/, errorCode=null, startTime=1749132684207, endTime=1749132688423]; responseBody=null].

Environment

VMware NSX

Cause

The above symptoms indicates connectivity or authentication issues with the SFTP server.

Resolution

• Restore the connectivity with the SFTP server, or validate the SFTP credentials to have sufficient permissions. 
• If no connectivity issues have been identified between the NSX manager and the SFTP server and the SFTP server path and permission limitations outlined in Broadcom KB 312385 are ruled out, execute a manual backup of the affected NSX Manager by clicking on the start backup button/re-apply the credentials(username,password) in the NSX backup configuration.

Additional Information

• The behavior where the Node & Cluster backups will show "Successful" while the Last Backup Status is shows "Failed" is as per design. The Node & Cluster backup status indicates that the backup was successfully created on the NSX manager. On the other hand, the Last Backup Status indicates the success of the transfer to the SFTP server, which in that scenario failed.
• If the issue is not caused by connectivity or authentication issues with the SFTP server, please review the below KBs

NSX backup fails with "Backup operation unknown error"

NSX-T Manager Backup task never completes

"Authentication failed", "bad directory" or "server disk full" error when preforming NSX backup to Windows SFTP server

NSX Scheduled backups do not execute at the scheduled time, but manual backups are successful.

Troubleshooting NSX Backup and Restore Failures