Troubleshooting Inconsistent ACL Rule Application With Deny All Policy In DefGuard V1.4.0

Introduction

This article addresses a peculiar issue encountered in DefGuard v1.4.0, where Access Control List (ACL) rules combined with a default location policy of "Deny All" exhibit inconsistent behavior. Specifically, the issue revolves around ICMP traffic being intermittently blocked for users despite a rule explicitly allowing it for a user group from Active Directory (AD). This article details the problem, the troubleshooting steps taken, and potential solutions, aiming to provide insights and guidance for those facing similar challenges. The focus is on understanding the root cause of this erratic behavior and implementing effective strategies to ensure consistent network access based on defined policies.

Problem Description

The core issue lies in the inconsistent application of ACL rules when a default location policy of "Deny All" is in effect. The setup involves a simple rule intended to allow ICMP traffic for a specific user group authenticated via Active Directory. Initially, some users within the group can successfully send and receive ICMP packets, while others experience complete blockage. This inconsistency is not immediately resolved and exhibits a delayed, almost random pattern. For instance, out of several users, a subset might face issues, which can then resolve themselves over time (e.g., after an hour), only to reappear for different users later. The problem is further compounded by the fact that users experiencing the issue are correctly identified and displayed in the DefGuard dashboard, indicating that the system recognizes their connection attempts but fails to apply the intended ACL rule consistently.

The intermittent nature of this issue makes it particularly challenging to diagnose. The problem manifests even when the affected users are attempting basic network operations, such as pinging the default gateway. The fact that the users appear in the DefGuard dashboard while experiencing connectivity issues suggests that the authentication and identification processes are functioning correctly, but the subsequent application of the ACL rule is failing. This disconnect between user identification and policy enforcement points to a potential bug or misconfiguration within the DefGuard system itself, specifically in how it handles ACL rules in conjunction with the "Deny All" default location policy. Understanding this behavior is crucial for maintaining network security and ensuring seamless user experience. This inconsistency can lead to significant disruptions in network operations and requires a thorough investigation to prevent future occurrences.

Symptoms Observed

The symptoms observed are quite specific and highlight the erratic nature of the issue. Initially, when the rule is set to allow ICMP traffic for users within a defined AD group, some users can successfully ping network resources, while others cannot. This issue isn't tied to a specific user; instead, it seems to affect users randomly. For instance, two users might have no issues, while a third user within the same group experiences complete blockage of ICMP traffic. This initial inconsistency is perplexing, as all users should theoretically be subject to the same ACL rule.

Over time, the situation can change spontaneously. After about an hour, some users who initially had problems might find that their ICMP traffic is now passing through without issue. However, this doesn't necessarily mean the problem is resolved, as other users may then start experiencing the same blockage. This shifting nature of the issue makes it extremely difficult to pinpoint the root cause. The fact that the problem appears and disappears seemingly at random suggests that there may be an underlying timing or caching issue within DefGuard. Moreover, the lack of any specific error messages on the client-side further complicates the diagnosis process. Users simply experience a failure to connect, without any indication as to why the connection is being blocked.

The temporary workaround of creating a rule to allow all traffic for the affected user and then removing it after a brief period further underscores the complexity of the problem. This action somehow resets or recalibrates the system, allowing the original ICMP rule to function correctly, at least for a while. This workaround highlights that the issue is likely not a persistent misconfiguration but rather a temporary glitch or state within DefGuard that prevents the proper application of the ACL rules. This behavior suggests a potential flaw in the system's rule processing or caching mechanism, which warrants a detailed examination.

Temporary Workaround Behavior

As mentioned in the problem description, a peculiar workaround was discovered that temporarily resolves the issue. When a user experiences ICMP traffic blockage, creating a temporary rule that allows all traffic for that specific user can alleviate the problem. This workaround involves adding a new ACL rule that overrides the default "Deny All" policy and the specific ICMP rule, effectively granting unrestricted access to the affected user. After a short period, typically around 5 to 10 minutes, this temporary rule can be safely removed. Following the removal, the original ICMP rule appears to function correctly for the user, allowing ICMP traffic as intended.

The effectiveness of this workaround is quite intriguing and provides valuable clues about the underlying issue. The fact that granting and then revoking full access resolves the problem suggests that DefGuard's ACL processing engine might have a temporary caching or state-management issue. When a user's traffic is initially blocked, the system might be incorrectly caching the "Deny All" policy or failing to properly evaluate the ICMP rule. Creating the temporary "allow all" rule forces the system to re-evaluate the user's permissions and update its internal state. Removing the rule then allows the system to correctly apply the intended ICMP rule.

However, this workaround is not a permanent solution and merely serves as a temporary fix. The underlying issue can recur, requiring the workaround to be applied repeatedly for different users. This makes the workaround cumbersome and impractical for large-scale deployments. The inconsistent nature of the problem and the need for a temporary fix further emphasize the need for a thorough investigation and a permanent resolution. This workaround's behavior hints at a deeper issue within DefGuard's rule processing logic, warranting further examination of the system's internal mechanisms.

DefGuard Environment Details

To provide a comprehensive understanding of the issue, it's essential to outline the specific environment in which DefGuard is operating. The DefGuard Core and Gateway versions are both running version v1.4.0. This information is crucial, as it allows for targeted investigation into known issues or bugs specific to this version. Furthermore, it helps in determining whether an upgrade to a later version might resolve the problem.

The DefGuard Gateway, which is responsible for enforcing the ACL rules and policies, is running on Debian 12. Debian 12 is a widely used and stable operating system, making it less likely to be the direct cause of the issue. However, understanding the underlying operating system is important for ruling out potential compatibility issues or conflicts. The specific version of Debian, along with any installed packages or configurations, can provide further context for diagnosing the problem.

Operating System and Version: Debian 12

Knowing the environment details helps narrow down the scope of the investigation and allows for targeted troubleshooting. It's possible that specific configurations or interactions between DefGuard and the operating system might be contributing to the problem. By considering these details, a more accurate diagnosis and effective solution can be identified.

Troubleshooting Steps Taken

To address the inconsistent ACL rule application, several troubleshooting steps were undertaken to isolate and identify the root cause. The initial approach involved a thorough review of the ACL rules and location policies within DefGuard. The aim was to ensure that the rules were correctly configured and that there were no conflicting policies that could explain the intermittent behavior. This involved examining the specific settings for the ICMP rule, verifying that the correct AD group was targeted, and confirming that the "Deny All" default location policy was indeed in effect.

Network connectivity tests were also conducted to verify the basic network infrastructure and rule out any underlying network issues. This involved pinging the default gateway and other network resources from the affected users' machines to confirm that the problem was specific to DefGuard and not a broader network issue. The results of these tests indicated that the network was functioning correctly, further narrowing down the potential causes to DefGuard itself.

Log analysis formed a crucial part of the troubleshooting process. DefGuard logs were examined for any error messages or warnings that might shed light on the issue. However, no relevant error messages were found that directly indicated the cause of the inconsistent ACL application. This lack of explicit error messages made the troubleshooting process more challenging, as it suggested that the problem might be a subtle bug or misconfiguration that was not triggering any specific alerts.

Packet captures were also considered as a potential troubleshooting step. Capturing network traffic on the DefGuard Gateway could provide detailed insights into the flow of ICMP packets and help determine whether the traffic was being dropped by the gateway or if there were any other anomalies. However, this step was not fully implemented due to the intermittent nature of the problem, which made it difficult to capture the issue in real-time. The sporadic behavior of the problem would require continuous packet capture, which could be resource-intensive and might not guarantee capturing the specific instance of the issue. Despite this limitation, packet captures remain a valuable tool for future troubleshooting efforts if the issue persists.

Possible Causes and Solutions

Given the symptoms and troubleshooting steps taken, several potential causes for the inconsistent ACL rule application can be identified. One possibility is a caching issue within DefGuard's ACL processing engine. The system might be incorrectly caching the "Deny All" policy or failing to properly update its cache when changes are made to ACL rules. This could explain why the temporary workaround of creating and deleting an "allow all" rule resolves the issue temporarily, as it might force the system to refresh its cache.

Another potential cause is a race condition within DefGuard's rule processing logic. If multiple users are attempting to access the network simultaneously, there might be a situation where the system is not correctly applying the ACL rules in the correct order. This could lead to some users being blocked while others are allowed, depending on the timing of their requests.

A third possibility is a bug within DefGuard v1.4.0 that specifically affects the interaction between ACL rules and the "Deny All" default location policy. It's possible that this version of DefGuard has a known issue that is causing the inconsistent behavior. Checking the DefGuard documentation and release notes for known bugs or issues related to ACL rules and location policies could provide valuable insights.

Based on these potential causes, several solutions can be considered:

1. Upgrade to the Latest DefGuard Version: Upgrading to the latest version of DefGuard might resolve the issue if it is a known bug that has been fixed in a later release. Checking the release notes for the latest version can confirm whether the issue has been addressed.
2. Review ACL Rule Order and Specificity: Ensure that the ACL rules are ordered correctly, with the most specific rules placed higher in the list. This can help prevent conflicts between rules and ensure that the intended rules are applied correctly.
3. Investigate Caching Mechanisms: Examine DefGuard's caching mechanisms to determine if there are any configuration options that can be adjusted to improve cache consistency. Clearing the cache might also be a temporary solution, but it's important to identify the underlying cause of the caching issue.
4. Implement Rate Limiting: If a race condition is suspected, implementing rate limiting on the DefGuard Gateway might help prevent the issue by limiting the number of requests processed simultaneously.
5. Contact DefGuard Support: If the issue persists despite these troubleshooting steps, contacting DefGuard support is recommended. They can provide further assistance and potentially identify specific bugs or configuration issues that are causing the problem.

Conclusion

The inconsistent application of ACL rules in DefGuard v1.4.0, when combined with a "Deny All" default location policy, presents a challenging issue. The intermittent nature of the problem, coupled with the lack of explicit error messages, makes diagnosis difficult. However, by systematically analyzing the symptoms, reviewing the environment details, and conducting thorough troubleshooting steps, potential causes can be identified. The possibilities of caching issues, race conditions, or specific bugs within DefGuard v1.4.0 warrant further investigation.

The temporary workaround of creating and deleting an "allow all" rule provides a temporary solution but is not a sustainable long-term fix. Upgrading to the latest DefGuard version, reviewing ACL rule order, investigating caching mechanisms, implementing rate limiting, and contacting DefGuard support are all viable options for resolving the issue. By addressing the root cause of the problem, consistent and reliable enforcement of ACL rules can be ensured, enhancing network security and user experience. Further investigation and implementation of appropriate solutions are crucial to prevent future disruptions and maintain a stable network environment.

Keywords for SEO:

• DefGuard ACL Rules
• Location Default Policy
• Deny All Policy
• ICMP Traffic
• Network Troubleshooting
• DefGuard v1.4.0
• Debian 12
• Access Control List
• Network Security
• Firewall Rules