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 fails.

- 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 you see errors similar to:

2025-06-05T14:11:28.457Z <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].

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

 

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. 

 

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 KB #312385.