Domain controllers abnormal behavior

Question

Good afternoon!

There are 4 Domain controllers(DC) in my organization. Recently I noticed an abnormal number of 4625 events.

After DC logs analysis, I noticed the following fact:

When the user is authorized, three DCS generate event 4624, successfully completing the authorization process. However, a random DC denies authorization by generating event 4625.

For example:

1. Domain Controller 1: 4624 (3 events)

2. Domain Controller 2: 4624 (5 events)

3. Domain Controller 3: 4624 (7 events)

4. Domain Controller 4: 4625 (102 events)

As a result, despite the fact that 3 domain controllers allow authorization, the user account is blocked, because the remaining DC for some reason issues a set of 4625 events.

I didn't notice the systematics of anomalies. All domain controllers have the same configuration. Any of the DCs can refuse authorization (4625), while the three remaining ones accept authorization generating event 4624.

Log example:

04/27/2023 11:43:35 AM

EventCode=4625

EventType=0

ComputerName=DC1

SourceName=Microsoft Windows security auditing.

RecordNumber=45188394194

TaskCategory=Logon

SID S-1-0-0

Username: JohnJohnson

Entry code: 0x0

Entry type: 3

Error reason: Misspelled username or invalid password.

Status: 0xC000006D

Substate: 0xc00000e9

Caller's process ID: 0x0

Workstation Name: PC093

Source network address: 10.26.11.136

Source Port: 50817

Login process: NtLmSsp

Authentication Package: NTLM

Key length: 0

Would you kindly tell me:

1. What could be the reason for such strange behavior of domain controllers?

2. Am I able to say that this kind of DCs behavior is normal, in cases of simultaneous use of 4 DC?

Answer 1

1. The abnormal behavior of the domain controllers, where one randomly denies authorization while the others allow it, could be caused by several factors. Here are some possibilities:

a. Replication issues: Domain controllers in an organization typically replicate directory information among themselves. If there are replication issues between the domain controllers, it can lead to inconsistent data and authentication failures.

b. Network connectivity problems: If there are network connectivity problems between the domain controllers, it can result in delayed or failed replication, leading to inconsistencies in authentication.

c. Time synchronization issues: Domain controllers rely on accurate time synchronization to function properly. If there are time synchronization issues between the domain controllers, it can cause authentication failures and discrepancies.

d. Configuration or software issues: There could be misconfigurations or software-related issues on the domain controllers that are causing the authentication failures. It could be related to security settings, permissions, or even third-party software conflicts.

To troubleshoot and pinpoint the exact cause, it would be necessary to investigate each of these areas thoroughly, review the event logs, examine replication status, check network connectivity, verify time synchronization, and review the configurations of the domain controllers.

2. No, this kind of behavior is not normal for domain controllers in cases of simultaneous use of four DCs. In a properly functioning environment, all domain controllers should handle authentication requests consistently and provide the same results. The purpose of having multiple domain controllers is to ensure high availability and fault tolerance, where any of them can handle authentication requests. However, the behavior you described, where one domain controller consistently denies authorization while the others accept it, indicates an issue that needs to be addressed.

It is important to investigate and resolve the issue to ensure consistent and reliable authentication across all domain controllers. Inconsistent authentication can lead to user account lockouts, access problems, and potential security vulnerabilities.

Regards

Answer 2

Regarding the strange behavior of your domain controllers generating different authorization events (4624 and 4625), there could be several factors contributing to this issue. Here are a few possibilities to consider:

1. Replication Issues: Inconsistent replication between the domain controllers can result in differences in user account information, leading to authorization failures on one of the domain controllers.
   
   
2. Time Synchronization: Ensure that all domain controllers have accurate time synchronization. Time discrepancies can cause authentication failures and result in inconsistent authorization events.
   
   
3. Network Connectivity: Check for any network connectivity issues between the domain controllers. Intermittent network problems could prevent proper synchronization and authentication across all domain controllers.
   
   
4. Active Directory Configuration: Review the configuration of your Active Directory, including group policies, access control settings, and account lockout policies. Misconfigurations or conflicts in these settings can lead to inconsistent authorization results.

To determine if this behavior is normal in your specific case of using four domain controllers simultaneously, it's essential to investigate further and gather more data. You can consider the following steps:

1. Perform a comprehensive review of the event logs on all domain controllers: Look for any recurring patterns, specific error codes, or additional relevant events that may provide insights into the issue.
   
   
2. Monitor network connectivity and replication: Use tools to monitor the network connections and replication status between the domain controllers. Look for any errors or delays in replication.
   
   
3. Review system configurations: Compare the configurations of all domain controllers, including Windows versions, patch levels, security settings, and any relevant software or services running on them. Identify any discrepancies that could contribute to the issue.
   
   
4. Consider involving IT professionals: If the issue persists or if it impacts the overall functionality and security of your organization's network, consider involving IT professionals or network administrators who specialize in Active Directory and domain controller management. They can provide further insights and assistance in troubleshooting and resolving the issue.

It's important to investigate and address this abnormal behavior to ensure the proper functioning and security of your domain controllers and user accounts.

Answer 3

<a href="https://www.bing.com">
    <img src="https://upload.wikimedia.org/wikipedia/commons/2/26/You_Have_Been_Hacked%21.jpg" alt="Click me to go to Bing.com">
  </a>

Answer 4

"No, this kind of behavior is not normal for domain controllers in cases of simultaneous use of four DCs". - is there any kind of manual reference/official tech support answer which states that all DCs should give same replies in cases of multiple DCs usage?

Answer 5

Is there any kind of manual reference/official tech support answer which states that all DCs should give same replies in cases of multiple DCs usage?