Thinking of Adding a Windows Server 2025 DC? Why It Might Cause Major Network Problems

Is Your Mixed Server Environment Safe? The Hidden Risks of a Windows Server 2025 Upgrade

If you help manage a computer network, this is for you. You might be thinking about adding a new Windows Server 2025 computer to act as a Domain Controller (DC). A Domain Controller is like the main traffic cop for your network, handling logins and security. The advice right now is simple: if your network also uses older servers like Windows Server 2022 or 2016 as Domain Controllers, do not add a 2025 server to the mix.

Putting a new Server 2025 DC into a network with older DCs is causing huge problems. People suddenly and randomly find they can’t log in. The computers themselves are failing to update their own secret passwords with the network. This isn’t a small glitch. One administrator described the situation by saying, “The roof is on fire!” This is because the problem strikes without warning and can disrupt your entire organization’s workflow.

This article breaks down exactly what is happening, why it is happening, and what you can do—and more importantly, what you should not do—to keep your network safe and stable. It is based on the real-world experiences of system administrators who have faced this issue head-on. Microsoft is reportedly working on a solution, but it has not been officially confirmed as a public issue yet. Until then, caution is the best approach.

The Core of the Conflict: Machine Passwords and Login Failures

Imagine your network is a private club. Every person who logs in has a password. But every computer that is part of the club also has its own secret password, called a machine account password. This is how the computer proves to the network that it is a trusted member and not an imposter. For security, these machine passwords are required to change automatically on a regular basis, usually every 30 days.

Here is where the problem starts. When a Windows Server 2025 DC is added to a network with older DCs, this automatic password change process breaks. The computers on the network try to update their password, but the process fails. After a while, the old password expires, and the computer is no longer trusted by the network.

The consequences of this failure are severe:

Random Login Failures

A user might try to log into their computer or a server and be denied access for no clear reason. The issue seems random. It might affect one server today and a different one tomorrow. This unpredictability makes troubleshooting incredibly difficult.

Loss of Trust

The formal term for this is that the “trust relationship” between the machine and the domain fails. The network essentially kicks the computer out of the club until its credentials can be fixed.

One administrator running a network with a mix of 2022 and 2025 Domain Controllers described the chaos perfectly. After adding the 2025 servers, logins would just stop working on random machines. His team discovered that the root cause was the failure of these machine accounts to reset their passwords. This issue is not just an annoyance; it can bring productivity to a halt.

The Technical Reason: An Old Encryption Method Called RC4

So, why does this happen? The evidence points to a change in how Windows Server 2025 handles an old and less secure encryption method known as RC4. Encryption is the process of scrambling data so only authorized parties can read it. It is the secret code language that computers use to talk securely.

RC4 is an outdated code language. For years, the tech industry has been moving away from it because it has known weaknesses that can be exploited by attackers. Modern systems prefer stronger, more complex encryption methods like AES. Windows Server 2025 continues this trend by further limiting or changing how it uses RC4.

The problem arises in a mixed environment because the older servers (like 2016 or 2022) may still expect to use or negotiate RC4 in certain situations. The new Server 2025 has a different set of rules for this old encryption. This mismatch in communication protocols appears to be what causes the machine password reset process to fail. The servers are essentially speaking different dialects of the same security language, leading to a critical misunderstanding.

The Danger of a “Simple” Fix

Seeing that RC4 was the problem, one administrator tried what seemed like a logical solution: disable RC4 completely across the network. They used a Group Policy Object (GPO), which is a tool for setting rules for all computers in the domain. The goal was to force all accounts to stop using RC4 for authentication requests.

The result was a catastrophe.

This action crippled the entire domain. No one could log in. The network was completely inaccessible. The administrator described the process of fixing it as a “hair-raising” session, requiring a complex, low-level tool called ADSI Edit just to reverse the change and allow RC4 again. This story serves as a stark warning: do not try to manually force RC4 to be disabled in this situation. The systems are too fragile, and you risk making the problem infinitely worse.

What Does and Doesn’t Work: Solutions from the Trenches

Administrators who have been battling this issue have tried several things. Most of them are temporary fixes or bad ideas, but one solution has proven effective, though it comes with its own major challenges.

The Temporary Workaround

When a machine’s trust relationship fails, there is a manual way to fix it. An administrator can log into the affected computer using a local account (one that isn’t tied to the network) and run a command:

reset-ComputerMachinePassword

This command forces the computer to get a new password from a Domain Controller. It works. But it is not a solution. It is a temporary patch. You would have to do this for every machine every time its password fails to update. For any network with more than a handful of computers, this is completely impractical.

An Idea to Avoid

Another administrator in an online forum suggested preventing the machine accounts from changing their passwords altogether. While this would stop the error from occurring, it is a very bad idea from a security perspective. Machine password rotation is a fundamental security feature. Disabling it would be like leaving your front door unlocked permanently to avoid the hassle of using a key. It makes your network significantly more vulnerable to attack.

The Only Known Effective Solution

The only method that has reliably solved the problem is to eliminate the mixed environment entirely. One administrator, who ultimately lost his job over the production downtime caused by this issue, shared his experience. He found that the only way to restore normal function was to upgrade all of his Domain Controllers to Windows Server 2025.

Why this works:

• When all DCs are running the same 2025 version, they all use the same updated Kerberos (the network’s authentication service) database and security protocols.
• The conflict between the new and old systems is gone because there are no old systems left in that critical role.

However, this “solution” is a massive project. It requires careful planning, potential downtime, and significant effort. For the administrator who shared his story, a lack of proper documentation and a rushed process led to a day of lost production and his dismissal. This highlights the high stakes involved. Upgrading all your DCs is not a quick fix; it is a full-scale infrastructure project that may not be feasible for many organizations right now.

Microsoft’s Position and Your Best Path Forward

As of late September 2025, this problem has not been officially acknowledged by Microsoft on its public Windows Server Release Health status page. This means there is no official documentation, no “known issue” article, and no patch you can download to fix it.

However, reports from administrators in contact with Microsoft suggest that the issue has been reported internally. The product group is said to be aware of the bug and is working on a fix. They are even providing weekly status updates to some who have reported it. But until that fix is developed, tested, and released to the public, everyone else is navigating this problem without official support.

Given this situation, the recommendation is clear and direct.

Do not introduce a Windows Server 2025 Domain Controller into a mixed environment.

If you are currently running Domain Controllers on Windows Server 2022, 2019, or 2016, you should postpone any plans to add a 2025 DC. The risk of causing random, disruptive failures across your network is simply too high. The best course of action is to wait for Microsoft to release an official statement and a patch that resolves the underlying Kerberos and RC4 conflict. Attempting to work around the issue could lead to even bigger problems, including extended network downtime and security vulnerabilities. Stay informed, follow updates from Microsoft, and for now, keep your DC environment consistent.