The answer is to stop unwanted traffic earlier and conserve bandwidth. An extended ACL is placed close to the source because it can filter traffic based on source and destination IP addresses, protocols, and port numbers, allowing it to drop malicious or unnecessary packets at the network edge before they traverse core routers and consume valuable link resources. On the CCNA 200-301 v2 exam, this concept tests your understanding of ACL placement strategy—a common trap is assuming extended ACLs belong near the destination, but Cisco emphasizes source-side placement for efficiency. A helpful memory tip is “Extended near the source, standard near the destination,” which reinforces that extended ACLs filter granularly early, while standard ACLs, which only check source IPs, are placed close to the destination to avoid blocking legitimate traffic.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Why is an extended ACL usually placed close to the source of the traffic being filtered?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To stop unwanted traffic earlier and conserve bandwidth
Extended ACLs can filter by source, destination, and protocol. Placing them near the source drops unwanted traffic before it crosses more of the network.
Key principle: Extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Because standard ACLs cannot be applied near the destination
Why it's wrong here
That is not the reason for extended ACL placement guidance.
When this WOULD be correct
In a different question asking about the limitations of standard ACLs, one might state that they cannot be applied effectively near the destination for complex filtering scenarios, thus making this option correct. For example, a question could ask why standard ACLs are not suitable for certain destination-based filtering tasks.
✓
To stop unwanted traffic earlier and conserve bandwidth
Why this is correct
Correct. Filtering near the source is the classic design guidance for extended ACLs.
Related concept
Extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control.
✗
To make NAT translation easier on inside interfaces
Why it's wrong here
That is not the primary ACL placement principle here.
When this WOULD be correct
In a scenario where the exam question asks about optimizing NAT configurations in a network, a candidate might be asked why certain ACLs should be placed on NAT devices. In this context, the option could be correct if the question implies that specific ACL placements can facilitate NAT operations.
✗
Because extended ACLs only work inbound on access interfaces
Why it's wrong here
Extended ACLs can be applied in multiple directions and places depending on design.
When this WOULD be correct
In a question asking about the limitations of extended ACLs, such as 'What is a restriction of extended ACLs on access interfaces?', option D would be correct, as it highlights that extended ACLs are indeed applied inbound on access interfaces.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓To stop unwanted traffic earlier and conserve bandwidthCorrect answer▾
Why this is correct
Correct. Filtering near the source is the classic design guidance for extended ACLs.
✗Because standard ACLs cannot be applied near the destinationWrong answer — click to see why▾
Why this is wrong here
Standard ACLs can be applied near the destination or source, but the placement guidance for extended ACLs is based on their ability to filter on source and destination IP addresses and ports, not on limitations of standard ACLs. The reason for placing extended ACLs near the source is to filter traffic early, not because standard ACLs cannot be applied near the destination.
★ When this WOULD be the correct answer
In a different question asking about the limitations of standard ACLs, one might state that they cannot be applied effectively near the destination for complex filtering scenarios, thus making this option correct. For example, a question could ask why standard ACLs are not suitable for certain destination-based filtering tasks.
Why candidates choose this
Students may confuse the placement rules for standard and extended ACLs, thinking that extended ACLs are placed near the source because standard ACLs are limited to destination-based filtering. However, standard ACLs are typically placed near the destination, but that is not the reason for extended ACL placement.
✗To make NAT translation easier on inside interfacesWrong answer — click to see why▾
Why this is wrong here
NAT translation is typically performed on routers or firewalls at network boundaries, and ACL placement for filtering is independent of NAT configuration. Placing an extended ACL near the source does not directly affect NAT translation; NAT uses its own rules and is not a factor in ACL placement decisions.
★ When this WOULD be the correct answer
In a scenario where the exam question asks about optimizing NAT configurations in a network, a candidate might be asked why certain ACLs should be placed on NAT devices. In this context, the option could be correct if the question implies that specific ACL placements can facilitate NAT operations.
Why candidates choose this
Students might associate ACLs with NAT because both are often configured on border devices, leading to the misconception that ACL placement is related to NAT. However, the primary reason for placing extended ACLs near the source is to filter traffic early, not to assist NAT.
✗Because extended ACLs only work inbound on access interfacesWrong answer — click to see why▾
Why this is wrong here
Extended ACLs can be applied inbound or outbound on any interface, not just inbound on access interfaces. The statement is factually incorrect; extended ACLs are versatile and can be placed in various locations depending on the filtering requirements.
★ When this WOULD be the correct answer
In a question asking about the limitations of extended ACLs, such as 'What is a restriction of extended ACLs on access interfaces?', option D would be correct, as it highlights that extended ACLs are indeed applied inbound on access interfaces.
Why candidates choose this
Students may think that extended ACLs are only effective when applied inbound because they filter traffic before it enters the router, but this is a misunderstanding. Extended ACLs can filter traffic in both directions, and placement near the source is a design choice, not a technical limitation.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Remember that ACLs are processed by network devices, not end devices, and their placement affects traffic flow, not the ACL's complexity or dynamic capabilities.
Detailed technical explanation
How to think about this question
Extended Access Control Lists (ACLs) are a fundamental security feature in Cisco networking that filter traffic based on multiple criteria such as source IP, destination IP, protocol type, and port numbers. Unlike standard ACLs, which filter only by source IP address, extended ACLs provide granular control over traffic flows, enabling network administrators to permit or deny specific types of traffic. This capability is essential for enforcing security policies and optimizing network performance by controlling which packets are allowed to traverse the network.
The placement of extended ACLs near the source of the traffic is a best practice because it prevents unwanted traffic from traveling across the network, thereby conserving bandwidth and reducing unnecessary load on intermediate devices. By filtering traffic as close as possible to its origin, the network avoids processing and forwarding packets that will ultimately be denied, which improves overall efficiency and security. This design principle contrasts with placing ACLs near the destination, which allows unwanted traffic to consume network resources before being dropped.
A common exam trap is misunderstanding the difference between standard and extended ACL placement. Some candidates incorrectly believe that extended ACLs must be placed near the destination or that they only work inbound on interfaces. In reality, extended ACLs can be applied inbound or outbound and should be placed near the source to maximize efficiency. Misplacing extended ACLs can lead to suboptimal network performance and security gaps, which is why understanding the rationale behind ACL placement is critical for the CCNA exam and real-world network design.
KKey Concepts to Remember
Extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control.
Placing extended ACLs near the source of traffic prevents unwanted packets from consuming network bandwidth and resources downstream.
Standard ACLs filter only by source IP and are typically placed near the destination to avoid blocking legitimate traffic prematurely.
Extended ACLs can be applied inbound or outbound on interfaces, providing flexible deployment options based on network design.
Filtering traffic early with extended ACLs improves network performance by reducing unnecessary processing on intermediate routers and switches.
Misplacing extended ACLs near the destination can lead to inefficient bandwidth usage and increased network congestion.
Understanding the difference between standard and extended ACL placement is critical to designing secure and efficient Cisco networks.
Cisco devices process ACLs in sequential order, so placing extended ACLs near the source ensures early denial of unwanted traffic.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — Extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control..
What is the correct answer to this question?
The correct answer is: To stop unwanted traffic earlier and conserve bandwidth — Extended ACLs can filter by source, destination, and protocol. Placing them near the source drops unwanted traffic before it crosses more of the network.
What should I do if I get this 200-301 question wrong?
Review extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Extended ACLs filter traffic based on source IP, destination IP, protocol, and port numbers, enabling granular traffic control.
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