Diagnosing Intermittent Authentication Failures for Service Accounts in vSphere

Products

• VMware vCenter Server

Issue/Introduction

After applying a vCenter patch update, some users may experience intermittent authentication failures for service accounts, particularly those used for backup operations. These failures can occur despite no changes being made to the service accounts themselves.

Environment

- vSphere 7.0 or later
- Environment using Active Directory for authentication
- vCenter Servers in the environment
- Service accounts used for operations such as backups

Cause

Intermittent authentication failures are often caused by Active Directory replication issues or DNS inconsistencies. These problems can be exacerbated by networking and other infrastructure performance factors, leading to:

1. Kerberos pre-authentication failures
2. Inability to find user or group information in Active Directory
3. Rapid switches between successful and failed authentication attempts

Resolution

Follow these steps to resolve the intermittent authentication issues:

1. Verify Active Directory Replication:
   a. Open the Active Directory Sites and Services console.
   b. Navigate to the "Sites" container and expand your site.
   c. Check the "NTDS Settings" for each domain controller.
   d. Ensure all replication partners are up-to-date.

2. Check DNS Resolution:
   a. Log into the ESXi host command line console.
   b. Run `cat /etc/resolv.conf` to list DNS servers.
   c. For each DNS server, run:
      `nslookup <ESXi_hostname> <DNS_server_IP>`
      `nslookup <ESXi_IP_address> <DNS_server_IP>`
   d. Ensure all lookups resolve correctly.

3. Verify Network Connectivity:
   a. From each vCenter server, ping the domain controllers.
   b. From each ESXi host, ping the vCenter servers and domain controllers.
   c. Ensure there are no packet losses or high latencies.

4. Review Load Balancing Configuration:
   a. If using a load balancer for authentication requests, check its configuration.
   b. Ensure session persistence is properly configured to prevent rapid switches between authentication sources.

5. Run the VCF Diagnostic Tool for vSphere (VDT):
   a. Download VDT from the VMware website.
   b. Run VDT on each affected vCenter server.
   c. Review the results, paying special attention to DNS and authentication-related checks.

6. Update vCenter's Identity Provider:
   a. Log in to the vSphere Client.
   b. Navigate to Administration → Single Sign On → Configuration.
   c. Select the identity source for your Active Directory.
   d. Click "Edit" and review the settings.
   e. Update the primary and secondary domain controller information if needed.

7. Consider Transitioning to AD over LDAP:
   a. If using Integrated Windows Authentication (IWA), plan to transition to AD over LDAP.
   b. Refer to VMware documentation for the transition process.

Additional Information

• Deprecation of Integrated Windows Authentication
• Active Directory over LDAP and OpenLDAP Server Identity Source Settings
• Using the lw-measure tool to detect latency between vCenter Server and Active Directory domain controllers
• Using checkADConfig to detect connectivity and DNS issues between vCenter Server and Active Directory