Access Control Lists (ACLs): What They Are, How They Work, and Best Practices

ACLs or Access Control Lists are used by the network administrators to specify certain permissions and what is more important for performance and security purposes. Here, we will discuss various type of ACLs, their practices of implementation, and much more.

Understanding Access Control Lists (ACLs)

ACLs or Access control lists are extremely important for controlling access to certain resources. This is crucial for the management process in general and for security reasons in particular.

Network administrators are using this approach to control the network in terms of which users have access to which part of the network. The set of rules is extremely important for the permissions in the network traffic. That means the network stays efficient and secure.

These rules function as gatekeepers and are used in the switches, routers, and firewalls. So, all the traffic activity is filtered depending on specific criteria such as ports, IPs, protocol types, and much more. That means unauthorized users have no chance to access specific data.

All the rules are used for outgoing/incoming traffic activity on a network device. The activity of a specific group of users can be fully denied by the set permissions. For instance, you can deny activity from the untrusted IPs.

With the right approach towards the implementation of ACLs, it is possible to exclude lots of security risks including cyber threats. This approach is equally beneficial for huge corporations and small businesses.

How Access Control Lists Function

ACLs can be compared with a set of rules. With the help of these rules, specific criteria are set for the packets, and once the criteria are matched a certain action should be taken. Usually, it is a denial of access or permit. The process functions according to the top-down order so it checks all the rules until something is matching.
The conditions under which the access is denied or allowed might be the following:

• Destination IP. With the usage of such a rule, you are specifying IPs to which the traffic will follow. So, you can control the access to specific servers.
• Source IP. It determines the IPs from which the traffic is going. This means you can allow traffic activity from specific IPs.
• Port numbers. It is possible to specify the port numbers that will be connected with the certain traffic. For instance, you might allow HTTP traffic on port 80 and deny FTP on port 21.
• Type of protocol. Depending on the used type of protocol the traffic activity can be allowed or denied.
• Additional parameters. These may relate to any parameters for additional control of the available traffic activity.

The process of ACL check goes as follows – once the network packet gets to the device, it will be checked according to all available rules (and based on rules the packet will be allowed/denied). In case, the matching rule won’t be found, according to the default setting the access will be denied.

For instance, admins can block specific IPs and allow access to all the others that are not included in the denied range of addresses. In this case scenario, incoming packets will be checked and blocked/allowed depending on the match.

Different Types of Access Control Lists

To guarantee the best possible level of protection, you should clearly understand different types of access control lists and their use case. So, let’s discuss each type in detail so you can create a more secure network.

1. Standard ACLs

This is probably the simplest possible variant that is mainly oriented on the usage of IP for filtering purposes. The traffic activity is allowed or denied only based on the IP of the user. This approach doesn’t have any differentiation between protocols and types of traffic. The only thing that matters is where this traffic is coming from.  

For instance, you can block traffic volumes that are coming from certain workstations with IP 232.232.3.13. Just make a standard rule where access from this specific IP will be denied.

2. Extended ACLs

To create more detailed rules, you should better try extended ACLs. This type gives more flexibility in terms of adding different criteria such as the type of the protocol, port numbers, destination/source IP, and much more.

For instance, you can allow HTTP traffic to a certain IP while denying all the other volumes of traffic.

3. Named ACLs

This type is way easier in terms of management because you can create a descriptive name and don’t use a numerical identifier. This approach is considered to be simpler, especially if working with lots of ACLs. This type might be extended or standard, with the first variant you can get improved manageability.

For instance, instead of IP usage, you can specify the name as “Deny_Marketing_Departmet”. The management with such an approach is much more simplified.

4. Dynamic ACLs

This approach is fully based on the user authentication process. That means the access will be given only for the session or a short duration period after the successful completion of the authentication. Temporary ACL entry is easily created so that users can securely access necessary resources.

For instance, there is a remote user that requires temporary access and that can be easily done with this type of ACL.

5. Reflexive ACLs

This type of ACL is used for the creation of temporary rules that allow access based on outbound traffic. This variant can be used when internal clients want to access external resources, but at the same time, you plan to restrict undesirable inbound traffic.

For instance, an internal client wants to access some external resources, and temporarily the permission will be allowed, but only during the session that was initiated by the internal client.

6. Time-Based ACLs

As obvious from the name, it is necessary for the rules to be set based on the time. Such type can be used when there is a necessity to restrict access during off-hours or other possible scenarios of restrictions.

For instance, the admin might need to set these ACLs during working hours and the access will be allowed only to certain network parts. The access to the same resources will be denied during other hours.

Best Practices for Implementing ACLs

Here are some helpful practices that can significantly minimize security risks and even some operational difficulties.

1. Establish Clear Objectives

Prior to actually setting any ACLs, you should write down your major aims that should be reached with this type of implementation. You should clearly see the goals in either stopping some type of traffic activity or restricting access to some networking parts. Your needs are first and only then try to find the most suitable approach to achieve them.

2. Follow the Principle of Least Privilege

To achieve the highest possible level of security, you should follow the principle of least privilege. This means devices as well as users get the minimal access level to complete the necessary task. You allow only specific traffic while denying all the rest by default.  

3. Maintain Proper Documentation

Every ACL rule should be not a random decision, but a choice that is necessary for the security and general effectiveness of the team. That’s why, it is crucial to describe the purpose of each rule so that further maintenance and troubleshooting will go smoother. Moreover, the network team should clearly understand the goals behind any decision that has been made regarding the rules.

4. Test ACLs in a Controlled Environment

One more practice that is highly important relates to the testing process of ACL rules. The deployment should be initially made in a controlled environment so that no harm will be done to the live network. Once everything is tested and everything is functioning as planned, it is possible to deploy the rules in the production environment.

5. Apply ACLs Close to the Source

To minimize the security risks even more, you should plan the implementation of ACLs that are close to the source. This means you should filter unauthorized users or undesirable traffic activity earlier so that it won’t provoke serious consequences in the long run.

6. Conduct Regular Reviews and Updates

Cyber-attacks are regularly changing and improving in order to reach their final result so the same should be done with the ACLs. You could not set some effective rules and use them for years because they soon become ineffective to the new risks. That’s why, regular checks and updates are necessary for the effectiveness of this approach.

7. Define Specific and Granular Rules

For more effective functioning, the rules should be as specific as possible. Just blocking a huge range of IPs might not be an ideal choice. The best variant will be the detailed specification of the protocols, specific IPs, or port numbers.

8. Utilize Comments for Better Clarity

Lots of devices allow to addition of variable comments to ACL configuration. That can be extremely important, especially with troubleshooting. Just by reviewing a detailed explanation of the specific rule, you can greatly minimize the time that can be spent on the search or investigation or more. Short command can be extremely necessary and it provides valuable context for the rule.

9. Enable Logging and Monitoring

One more great practice is the usage of logging for accessing ACLs so you can easily monitor undesirable traffic activity. By regular checking of the logs, you can immediately react to the undesirable activity. Moreover, it is possible to notice traffic patterns, detect security incidents, and quickly identify connectivity issues.

10. Prioritize Rule Order for Efficiency

To improve the performance, you should also consider the choice of the rule prioritization. For instance, use the most frequently matched options at the beginning so you can save lots of time on unnecessary checks. Moreover, you can set all the allowing rules at first and only then use the denying.

The Significance of Access Control Lists

Here are some benefits that you are getting together with the implementation of the access control lists.

1. Strengthened Security Measures

This is one of the great methods for strengthening security in general. You protect your data by determining which traffic is considered to be safe and which is not and denying its access. There are lots of online risks, so with the help of ACLs, admins can significantly minimize the possibility of DoS attacks, malware, data leakages, and much more.

2. Efficient Traffic Management

To get the highest possible level of reliability, it is crucial to work with traffic management. Effective management impacts the performance characteristics significantly and excludes harmful traffic and its potential effect on productivity.

3. Ensuring Regulatory Compliance

There are lots of industries that are extremely strict towards privacy and security standards. To comply with such serious regulations, ACLs can be a great option. ACLs can be configured in a way that will fully meet specific standards. For instance, GDPR (Data Protection Regulation), HIPAA, and PCI-DSS.

4. Granular Access Control

Granular access control gives lots of benefits regarding implementation of the specific security rules. This means that admins can create access rules that will greatly work with the needs of specific users, departments, and more. For instance, with the help of ACLs, you can create an environment where you can give the access to sales department for external resources and restrict this access to others.

5. Enhanced Network Visibility

Implementation of logging practice together with ACLs will show you the usual patterns that might be necessary for the future restrictions of traffic. By checking the logs activity, you can easily identify network problems, and suspicious activity, and make more informed decisions in general.

6. Protection Against Insider Threats

Lots of insider threats can be significantly minimized with the implementation of ACLs. The usage of strict access control and the limitations of most unnecessary actions within the network can reduce unauthorized access, data leakages, and other threats.

7. Cost-Effective Security Solution

This security solution is way cheaper when compared with other available measures that can be used. To begin with, it can be built into any possible device such as firewalls, routers, and switches. That means companies don’t require any additional investment into the hardware. This is a fantastic method of protection for companies that don’t want to overpay for security solutions.

8. Facilitates Network Segmentation

For the simplification of the management process as well as improving security level – network segmentation is a crucial factor. The network can be divided into specific zones. Moreover, every segment will have separate access control. This approach prevents the spread of potential threats within the network.

Key Takeaways

For the improvement of the security level as well as the implementation of efficient traffic management a great option is to choose ACLs. This approach is extremely effective for complying with regulatory requirements, improving the management process of network resources, and even defining security policies.