Microsoft tests the 15-character limit of Windows Server admins' patience

The May 12 security update introduced a bug affecting domain controller discovery when a server hostname is exactly 15 characters long. DCLocator calls such as nltest /dsgetdc:<domain> /pdc can return ERROR_INVALID_PARAMETER, preventing applications and administrative tools from locating a domain controller. Any functionality depending on domain controller lookup may stop working. Microsoft specifically cited Distributed File System (DFS) Namespace management as an example, since DFS Namespaces groups shared folders across servers into a single namespace and relies on domain controller discovery to resolve paths. Microsoft provided no workaround, but changing the hostname length to something other than 15 characters may avoid the issue. Windows Server 2016 remains supported through extended support and Extended Security Updates.

"When the hostname is 15 characters long, DCLocator calls (for example, using nltest /dsgetdc:<domain> /pdc) will return ERROR_INVALID_PARAMETER, preventing applications and administrative tools from locating a domain controller."

"In other words, anything that depends on a domain controller lookup might stop working. As an example, Microsoft gave Distributed File System (DFS) Namespace management, which would certainly be inconvenient. DFS Namespaces is a Windows Server role that allows admins to group shared folders across different servers into a single namespace. A single path can lead to files located on multiple servers. Unless, of course, the domain controller lookup is broken."

"Microsoft lists no workaround for affected users, though changing the server hostname to something other than 15 characters would presumably avoid the trigger. "The issue is under investigation, and additional information will be shared as soon as it becomes available," it said."

"Microsoft still officially supports Windows Server 2016. Mainstream support ended in 2022, but extended support will continue until January 12, 2027. Microsoft is offering up to three more years of support via the Extended Security Updates (ESU) program after that."

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