In networking, Access Control Lists (ACLs) play a crucial role in controlling traffic flow. But when it comes to ACL placement, the question arises: where should you apply your access list? In this article, we will explore the optimal location for ACL placement and shed light on the best practices associated with it.
Contents
Standard Access Lists vs. Extended Access Lists
Before diving into ACL placement, let’s briefly differentiate between standard and extended access lists. Standard access lists are primarily used to filter traffic based on source IP addresses, whereas extended access lists offer more granularity by considering both source and destination IP addresses.
Finding the Right Placement
To understand the optimal location for ACL placement, let’s take a look at a network topology consisting of three routers and multiple hosts. The goal is to prevent host C from communicating with host A while allowing it to communicate with host B and the internet.
We can configure a standard access list on any router interface along the path between host C and host A. However, the key is to find the best location that achieves the desired result without inadvertently blocking additional traffic.
Applying the Standard Access List
If we apply the access list on Router 3, filtering inbound traffic, it successfully prevents host C from communicating with host A. However, it also blocks host C’s communication with host B and the internet. The same result occurs when applying the access list on Router 1 or Router 2.
Moving forward, we find that applying the access list on Router 3, filtering outbound traffic, solves the problem. Now, host C is prevented from speaking to host A while maintaining its ability to communicate with host B and the internet. This optimal placement ensures that only the intended traffic is blocked.
Extended Access Lists: More Granularity, More Options
When dealing with extended access lists, which offer greater specificity, you have the flexibility to apply them anywhere as long as the access conditions are precisely defined. The general best practice is to apply extended access lists closest to the source to drop packets as early as possible.
Considerations for applying extended access lists include identifying aggregation points in your network topology. By analyzing your network’s structure, you can determine the most suitable locations for applying extended access lists. This approach allows you to prevent unwanted traffic while minimizing unnecessary processing by network devices.
FAQs
Q1: Can extended access lists do everything that standard access lists can?
Yes, extended access lists can accomplish everything that a standard access list can. In fact, extended access lists offer more granularity and should be preferred in real-world scenarios.
Q2: What is the best practice for ACL placement?
For standard access lists, apply them closest to the destination. For extended access lists, apply them closest to the source.
Q3: Should I avoid using standard access lists in the real world?
It is recommended to avoid standard access lists in favor of extended access lists. Extended access lists offer greater flexibility and control over traffic filtering.
Conclusion
Choosing the right location for ACL placement is crucial for effectively controlling traffic in your network. By applying standard access lists closest to the destination and extended access lists closest to the source, you can achieve your desired filtering goals while minimizing unintended consequences.
Remember, when it comes to ACL placement, it’s essential to consider the unique characteristics of your network and identify aggregation points for optimal results. Embrace the power of extended access lists to have more granular control over your traffic filtering.
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