Windows Server 2016 fails to find domain controller

Microsoft says a May 2026 security update breaks domain controller discovery on Windows Server 2016 systems with exactly 15-character hostnames.

The DCLocator lookup fails with ERROR_INVALID_PARAMETER, affecting tools like nltest and potentially DFS Namespace access.

Machines with 14- or 16-character hostnames are not impacted, and Microsoft has not announced a fix timeline yet.