What is the primary function of vCenter Single Sign-On (SSO) in a vSphere environment? 

vCenter Single Sign-On acts as an authentication broker and security token exchange infrastructure. It allows various vSphere software components to communicate with each other securely through a token exchange mechanism, rather than requiring each component to authenticate a user separately with a directory service like Active Directory. Source:,

What is the VMware Certificate Authority (VMCA) and how is it used by default?

VMCA is vSphere’s internal certificate authority included with every vCenter installation. By default, it provisions all necessary certificates for vCenter components and ESX hosts, using VMCA as the root certificate authority. This configuration secures the solution immediately upon installation with the lowest operational overhead. Source:,

List the external identity providers supported by vCenter in vSphere 9.0.

vCenter supports the following external identity providers for federated authentication:

• Active Directory Federation Services (AD FS)
• Okta
• Microsoft Entra ID (formerly Azure AD)
• PingFederate Source:

What is the VMware Endpoint Certificate Store (VECS)?

VECS is a local (client-side) repository running on every vCenter node that stores certificates, private keys, and other certificate information. It contains keystores such as MACHINE_SSL_CERT, TRUSTED_ROOTS, and solution user stores (e.g., vpxd, machine). It does not store ESX host certificates, which are stored locally on the hosts. Source:,

Differentiate between “Simple Authentication” and “Token-Based Authentication” in vCenter SSO.

• Simple Authentication: The user name and password are passed directly to vCenter, which validates the credentials against its configured identity sources.
• Token-Based Authentication: An external identity provider (like AD FS) authenticates the user and issues a token. vCenter uses this token to log the user in, never handling the user’s password directly. Source:

What is the default vCenter Single Sign-On domain name, and can it be changed? 

The default domain name is vsphere.local. You can change this domain name during the deployment of the vCenter appliance to a unique name, provided it does not conflict with other directory services like OpenLDAP or Active Directory. Source:

How can an administrator monitor the expiration of vCenter certificates?

vCenter automatically monitors all certificates in the VMware Endpoint Certificate Store (VECS). It issues an alarm in the vSphere Client when a certificate is 30 days or less from its expiration date. The threshold for this warning can be configured in Advanced Settings. Source:

What is the purpose of the “Machine SSL certificate” on a vCenter node?

The Machine SSL certificate is used to create an SSL socket on the server side for secure communications (HTTPS or LDAPS). It is used by the reverse proxy service, the vCenter service (vpxd), and the VMware Directory Service (vmdir) for server verification and encryption. Source:

Explain the user login flow when vCenter Identity Provider Federation is configured with AD FS.

1. The user enters their user name on the vCenter landing page.
2. vCenter redirects the authentication request to AD FS.
3. AD FS prompts the user for credentials and authenticates them against Active Directory.
4. AD FS issues a security token containing group information.
5. vCenter validates the token and logs the user in, granting access based on the group memberships defined in the token. Source:

Describe the “Hybrid Mode” approach to certificate management and why an organization might choose it.

In Hybrid Mode, the administrator replaces the Machine SSL certificates (which handle external/browser traffic) with custom certificates signed by a third-party or enterprise CA. However, they allow VMCA to continue provisioning and managing the internal Solution User and ESX host certificates. This approach secures external traffic with trusted certificates while minimizing the operational overhead of managing internal certificates. Source:,

How does vCenter manage users and groups when configured with Okta, Microsoft Entra ID, or PingFederate versus AD FS?

• Okta/Entra ID/PingFederate: vCenter uses the System for Cross-domain Identity Management (SCIM) 2.0 standard. The external IDP pushes users and groups to vCenter.
• AD FS: vCenter does not use SCIM. Instead, it uses an LDAP connection (configured during setup) to search the Active Directory domain for users and groups to map permissions. Source:,

What is the role of VMware Identity Services in an Enhanced Linked Mode (ELM) configuration when using an external IDP like Okta?

In an ELM configuration, VMware Identity Services runs on all nodes, but only one vCenter instance communicates directly with the external identity provider (e.g., Okta). The other vCenter nodes access the identity provider endpoint through this primary node. If the primary node fails, an activation script must be run on a secondary node to re-establish communication with the external IDP. Source:,

You need to generate a custom Certificate Signing Request (CSR) for a Machine SSL certificate. What are the specific technical requirements for the certificate fields?

• Key Size: 2048 to 8192 bits (RSA).
• Format: PEM encoded, x509 version 3.
• SubjectAltName: Must contain DNS Name=<machine_FQDN>.
• Key Usage: Must contain Digital Signature and Key Encipherment.
• Client/Server Auth: Extended Key Usage should generally be empty or contain Server Authentication; “Client Authentication” is not supported for Machine SSL certificates. Source:,

Explain the process of making VMCA an Intermediate Certificate Authority (CA).

1. Generate a CSR for the VMCA Root Signing certificate using the vSphere Certificate Manager (Option 2) or certool.
2. Submit the CSR to the enterprise/third-party CA.
3. Obtain the signed certificate and the full chain of intermediate/root certificates from the CA.
4. Combine the certificates into a single file (VMCA cert + Intermediate certs + Root cert).
5. Import this combined certificate back into vCenter using the Certificate Manager (Option 2), replacing the existing VMCA root. VMCA will then sign all subsequent certificates with this trusted chain. Source:,

What is the procedure to activate a secondary vCenter node for external IDP authentication in an ELM configuration if the primary node becomes unavailable?

1. Log in to the secondary vCenter shell.
2. Run the python script /usr/lib/vmware-trustmanagement/vmware_identity_services_activation.py activate.
3. Log in to the vSphere Client of this secondary node and retrieve the new Tenant URL and Redirect URI.
4. Update the OAuth2 registration and SCIM Push configuration on the external Identity Provider (e.g., Okta/Entra ID) with these new URLs. Source:,

What is the specific function of the vpxd-extension solution user store in VECS?

The vpxd-extension store contains the certificate for the vCenter extensions service. This includes services such as vSphere Auto Deploy, the inventory service, and other services that are not part of the standard vpxd (vCenter daemon) or vsphere-webclient solution users. Source:

How do you regenerate the STS (Security Token Service) signing certificate using the vSphere Client, and what is the impact on linked vCenters?

• Action: Navigate to Administration > Certificate Management > STS Signing, select the certificate, and click Refresh with vCenter Certificate.
• Impact: VMCA issues a new certificate and replaces the current one in vmdir. In an Enhanced Linked Mode configuration, vmdir automatically uploads the new certificate to all linked vCenter systems. A restart of vCenter services is generally not required for vSphere 8.0 and later. Source:,

Describe the purpose and usage of the dir-cli command-line utility.

dir-cli is used to interact with the VMware Directory Service (vmdir). It allows administrators to create and update solution users, manage passwords, manage global users/groups, and publish or unpublish trusted root certificates to the directory service. Source:,

When configuring vCenter Identity Provider Federation for AD FS, why must you provide the “Base distinguished name for users/groups” during setup?

Because vCenter needs to establish an LDAP connection to the Active Directory domain to search for and map AD users and groups to vCenter roles (Authorization). AD FS handles the authentication, but vCenter handles the authorization mapping via this LDAP connection. Source:

If you accidentally delete a user in vCenter that was synced via SCIM from an external IDP, how must you restore them?

You cannot simply “push” the user again from the IDP immediately. You must update the SCIM 2.0 application on the external IDP to unassign and then re-assign the user or group. This triggers a new synchronization event that restores the user in vCenter. Source:

What happens to custom certificates on an ESX host during a vCenter upgrade?

If an ESX host is provisioned with custom certificates, the upgrade process retains them, even if they are expired. However, if the host was provisioned with Thumbprint (self-signed) certificates, they are replaced with VMCA-signed certificates during the upgrade to ESX 8.0 or later. Source:

What is the vecs-cli entry getkey command used for, and what output does it produce?

This command retrieves a private key stored in a specific VECS store (e.g., MACHINE_SSL_CERT). It can output the key to a specified file path or display it as human-readable text in the terminal. Source:

Explain the “Maximum Token Renewal Count” in the vCenter SSO Token Policy.

It specifies the maximum number of times a token can be renewed. Once a token has been renewed this many times, it cannot be renewed again, and the user or service must re-authenticate to obtain a new security token. Source:

How does vCenter handle certificate revocation (CRLs) for internal vSphere components?

vSphere supports replacing compromised certificates but does not enforce certificate revocation (CRLs) for ESX hosts or vCenter systems by default. If a certificate is compromised, the administrator must explicitly remove the compromised certificate from the trust stores on all nodes. Source:

When using the certool CLI to generate a certificate, what file serves as the input for configuration options, and where is the default template located?

certool uses a configuration file (often named certool.cfg) to populate certificate fields like Country, Organization, and Hostname. The default template is located at /usr/lib/vmware-vmca/share/config/certool.cfg. Source:,