What is ACL-Based Rate Limiting?

Before we go into the details, let's start with the basics. ACL stands for Access Control List. In networking, an ACL is like a set of rules that controls which data packets are allowed to pass through a network and which are blocked. Think of it as a security checkpoint that decides who gets in and who doesn’t.

Rate limiting, on the other hand, is the practice of controlling the amount of data traffic allowed to flow through a network. It’s like putting a speed limit on a highway to prevent accidents. By limiting the rate at which data packets are allowed to travel, you can prevent the network from getting overloaded and ensure that important traffic gets through smoothly.

When we combine these two concepts, we get ACL-based rate limiting. This is a technique where the rules defined in an ACL are used to control the speed at which data is allowed to flow through the network. It's a smart way to manage network traffic, especially when there are a lot of users or devices trying to access the network at the same time.

Understanding ACL-Based Rate Limiting Traffic Policies

Now that we know what ACL-based rate limiting is, let's talk about traffic policies. In the context of networking, a traffic policy is a set of rules that define how data traffic should be managed. When it comes to ACL-based rate limiting, traffic policies are the tools we use to enforce the rate limits on data traffic.

A traffic policy consists of two main parts

• Traffic Policy Name: This is a label or identifier for the policy. It’s usually a string of up to eight characters that helps network administrators easily identify and manage different policies.
• Traffic Policy Definition (TPD): This is where the actual rules and commands are defined. The TPD can define various types of policies, such as rate limiting, counting the number of packets that match the ACL rules, or a combination of both.

Types of ACL-Based Rate Limiting

When setting up ACL-based rate limiting, there are two main types you can choose from: Fixed Rate Limiting and Adaptive Rate Limiting. Let's take a closer look at each.

Fixed Rate Limiting

Fixed rate limiting is like setting a strict speed limit on a highway. It enforces a strict bandwidth limit, meaning that any data traffic that stays within the limit is allowed to pass through, while any traffic that exceeds the limit is either dropped (blocked) or forwarded at the lowest priority. This type of rate limiting is useful when you want to ensure that certain types of traffic don’t hog all the bandwidth, leaving other important traffic with little to no access.

Adaptive Rate Limiting

Adaptive rate limiting is a bit more flexible than fixed rate limiting. Instead of strictly enforcing a limit, it allows for occasional bursts of traffic above the set limit. This is useful in situations where traffic may temporarily spike, such as during a video conference or a large file download.

How to Configure ACL-Based Rate Limiting

Configuring ACL-based rate limiting might sound complicated, but it’s straightforward once you understand the steps. Here’s a step-by-step guide on how to set it up, using a RUCKUS FastIron device as an example.

Step 1: Create a Traffic Policy

The first step in setting up ACL-based rate limiting is to create a traffic policy. This involves defining the policy name and setting up the rules that will govern how traffic is handled.

Step 2: Add the Traffic Policy to an ACL Entry

Once the traffic policy is created, the next step is to add a reference to this policy in an ACL entry. An ACL entry is like a rule that defines which traffic is allowed to pass through the network and which isn’t. By adding the traffic policy to the ACL entry, you’re telling the network to apply the rate limit defined in the policy to any traffic that matches the ACL’s conditions.

Step 3: Bind the ACL to an Interface

The final step is to bind the ACL (which now includes the traffic policy) to a network interface. A network interface is like a door that data traffic uses to enter or exit the network. By binding the ACL to an interface, you’re effectively applying the rate limit to any traffic that passes through that interface.

Practical Examples of ACL-Based Rate Limiting

To help you understand how ACL-based rate limiting works in practice, let’s look at a few examples of how it might be configured in different scenarios.

Example 1: Limiting Bandwidth on a Virtual Interface

Let’s say you want to limit the bandwidth for all traffic passing through a virtual interface to 100 Mbps. You would create a traffic policy named “VIRT100” that defines a rate limit of 100 Mbps. Next, you would add this policy to an ACL entry that permits all traffic on the virtual interface. Finally, you would bind the ACL to the virtual interface, effectively capping the bandwidth for all traffic on that interface at 100 Mbps.

Example 2: Prioritizing Traffic on a VLAN

In this example, you want to prioritize voice traffic (such as VoIP) on a specific VLAN while limiting the bandwidth for other types of traffic. You could create two traffic policies: one that gives voice traffic the highest priority and another that limits the bandwidth for other traffic types to 50 Mbps.

Example 3: Dropping Excess Traffic on a Physical Interface

Suppose you want to ensure that no more than 200 Mbps of data passes through a physical Ethernet interface. You would create a traffic policy that defines a 200 Mbps rate limit and specifies that any traffic exceeding this limit should be dropped.

Best Practices for ACL-Based Rate Limiting

To get the most out of ACL-based rate limiting, it’s important to follow some best practices:

• Set Appropriate Rate Limits :- Choose rate limits that make sense for your network. If the limits are too strict, important traffic might get blocked. If they’re too lenient, the network might get overloaded. Balance is key.
• Monitor Traffic Regularly:- Keep an eye on how traffic is flowing through the network. If you notice that certain types of traffic are being blocked or slowed down too much, consider adjusting the rate limits or modifying the traffic policies
• Test Configurations Before Deploying:- Before Deploying: Before applying ACL-based rate limiting on a live network, test your configurations in a controlled environment. This helps you catch any potential issues and fine-tune the settinga for optimal performance.
• Ensure Compatibility with Other Security Tools:- ACL-based rate limiting should work alongside other security measures, such as firewalls and intrusion detection systems. Make sure that your traffic policies don’t interfere with these tools or create unintended security gaps.

Troubleshooting Common Issues

Even with the best planning, you might encounter some issues when configuring ACL-based rate limiting. Here are a few common problems:

• Traffic Not Being Limited: Double-check the ACL entries and traffic policies to ensure they’re correctly configured.
• Unexpected Traffic Drops: Consider raising the limit or adjusting the traffic policy if important traffic is being dropped.
• Network Performance Issues: Review the traffic policies and make sure they’re aligned with the network’s needs.

Conclusion

ACL-based rate limiting is a powerful tool for managing network traffic, ensuring that data flows smoothly and securely. By understanding the basics of ACLs, rate limiting, and traffic policies, you can effectively control how data moves through your network, preventing overloads and maintaining optimal performance.

Whether you're limiting bandwidth on a virtual interface or prioritizing traffic on a VLAN, ACL-based rate limiting gives you the control you need to keep your network safe and efficient.