vCenter Server backup failed due to stale network interface "eth0:upgrade"

Products

• VMware vCenter Server

Issue/Introduction

• vCenter Server file backup failed at 95% with the error message "BackupManager encountered an exception".
• vCenter Server upgraded with Reduced Downtime Upgrade (RDU).
• In /var/log/vmware/applmgmt/backup.log:
  
  2026-03-02T08:42:49.250 [20260302-003759-25148086] [MainProcess:PID-173593] [BackupManager::GenerateBackupMetadata:BackupManager.py:224] ERROR: PNID is not resolvable to any IP on theexisting system.


• The forward and reverse resolution of PNID with DNS are working correctly.
• There are two network interfaces 'eth0' and 'eth0:upgrade' in the vCenter Server from the output of 'ifconfig' and the IP address of 'eth0:upgrade' is private which can not reach out to DNS server. 

Environment

VMware vCenter Server 8.0.x
VMware vCenter Server 9.0.x

Cause

The stale network interface 'eth0:upgrade' is unable to reach out to DNS to do name resolution by default. The interface should only exist during the upgrade with RDU. It should be removed automatically after upgrade completed. In this instance, the interface is still present in vCenter Server after upgraded which should be removed.

Resolution

To resolve the issue:

1. Restarting vCenter Server can remove the stale network interface 'eth0:upgrade' automatically with 'ifconfig' double confirm.
2. Try backup again after restarting completed which will be successful. 

Additional Information

VCSA VAMI Backup Failed With Error 'PNID is not resolvable to any IP on the existing system'
Backup of vCenter Server fails at 95% with error "Backup job failed"
古いネットワーク インターフェイス「eth0:upgrade」により vCenter Server のバックアップが失敗する