Will User Network Mapped Drives break by Moving the file shares server form one domain to another domain?

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Will User Network Mapped Drives break by Moving the file shares server form one domain to another domain?

Woody Chiu at RASI 231

All users in our company have I and J network-mapped drives created by the AD GPO policy. The file share server is currently located in another forest/domain, which is trusted bi-directionally by our main forest/domain, where all users reside. Having said that, it means all user permissions on the shares have been allowing them to access those I and J file shares across the forest/domain, no problem. I want to bring the file server into our main forest/domain instead of continuously accessing the resource there through a trust relationship. What if I have the file server leave its forest/domain, and join it back to our main forest/domain? Will that break any of the users' I and J mapping? FYI. The file shares server's hostname will be retained unchanged. I am actually seeing the links probably won't break for those user references that are based on I and J mappings, but will break for those that reference by FQDN path, because the UNC path actually includes the server's domain in the path. Hope you can help!

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Marcin Policht 67,980 MVP Volunteer Moderator

Yep — in your scenario, the only thing that can break is access paths that reference the server's FQDN. Drive letter mappings using the shortname (\FileServer\Share) will continue to work, but any references using the old FQDN (\FileServer.OldDomain.com\Share) will fail, because the domain portion of the UNC path has changed.

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin

Woody Chiu at RASI 231 Reputation points

2025-09-12T13:39:55.4633333+00:00

I have just performed a preliminary scan of all Excel files containing the FQDN paths. There were over thirteen thousand Excel files containing that. There are many other file types I have not scanned. So, it is not feasible to move the server to our main domain. Do you have any suggestions on how to handle this situation? I hope to remove the forest/domain where the file server resides due to a business merger a couple of decades ago to simplify management and reduce attack surfaces. Regardless, the forest/domain's DC has been upgraded to Server 2022, even though the file server is still Server 2008 32-bit. What is the file and folder access performance penalty through a bi-directional trust relationship between two Server 2022s in two different forests/domains if I am stuck with this way. Ideally, the migrated file server in Server 2022 can be moved over to our main forest/domain. Is there anything that we can do to make this happen without breaking all the UNC links and path references in the files ?
Marcin Policht 67,980 Reputation points MVP Volunteer Moderator

2025-09-12T16:16:27.5333333+00:00

You can preserve all existing UNC paths when migrating or upgrading a file server by using a DNS alias. This approach allows clients to continue accessing the server using the original FQDN, such as \\FileServer.OldDomain.com\Share, even though the server itself has been moved or upgraded. By creating a CNAME record in DNS that points the old FQDN to the new server's hostname or IP address, all network requests to the old name are automatically resolved to the correct server.

To ensure that clients can connect over the alias, the server should be configured to allow SMB access via CNAMEs. This requires setting the DisableStrictNameChecking registry value on the server and, if clients on the same server need to access it via the alias, optionally configuring the BackConnectionHostNames registry value. These settings prevent Windows from blocking file sharing connections that use the alias instead of the server's actual hostname.

Kerberos authentication over the alias can be maintained by registering a Service Principal Name (SPN) for the alias on the server's computer account. For example, creating an SPN such as HOST/FileServer.OldDomain.com ensures that Kerberos can issue tickets for clients connecting through the alias. Without this SPN, clients would fall back to NTLM, which works but is less efficient and less secure than Kerberos.

The original share and folder structure on the server can be retained so that the only change experienced by users is the resolution of the hostname. This preserves all Excel links, scripts, shortcuts, and any other hard-coded UNC paths, allowing the server to be upgraded to a newer OS, such as Server 2022, or eventually moved to a new domain without breaking user access.

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin

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Will User Network Mapped Drives break by Moving the file shares server form one domain to another domain?

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