Scenario: A high number of Desktop OS machines are displaying as 'Unregistered' in Citrix Studio. However, Desktop OS machines that are registered are functioning as expected. What is the likely…

If the Delivery Controller itself could not register with DNS, no VDAs in the site would be able to register, not just a subset of machines.

The XML trust setting controls whether StoreFront or Web Interface XML requests are accepted by the Controller; it has no effect on VDA-to-Controller registration.

VDA registration uses Kerberos mutual authentication, not machine-level digital certificates, so the absence of a certificate does not cause unregistered status.

Each VDA must perform a DNS lookup to resolve the Delivery Controller address before it can initiate the registration handshake. When only specific Desktop OS machines are unregistered while others function normally, the fault is localized to those machines being unable to query or resolve DNS, blocking the registration process entirely.