The correct answer is that extended ACLs are processed in order until a matching permit or deny statement is found. This sequential processing is fundamental because Cisco IOS evaluates each rule from top to bottom, stopping at the first match, which makes the order of entries critical for effective traffic filtering. Extended ACLs offer granular control by filtering on source and destination IP addresses, protocol type, and port numbers, unlike standard ACLs which are limited to source-only filtering. On the ENCOR 350-401 exam, this concept tests your ability to design and apply ACLs for precise traffic filtering, often appearing in scenario-based questions where a common trap is forgetting the implicit deny any at the end or misapplying an extended ACL in the wrong direction on an interface. Remember the mnemonic "SDP" for what extended ACLs can filter: Source, Destination, and Protocol/Port.
350-401 ACLs and CoPP Practice Question
This 350-401 practice question tests your understanding of acls and copp. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
Which three statements about extended ACLs on Cisco IOS are true? (Choose three.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Extended ACLs can filter based on source and destination IP addresses.
Extended ACLs can filter based on source and destination IP addresses, protocol, and port numbers. They are processed sequentially until a match is found, and an implicit deny any is at the end. They can be applied to interfaces using the 'ip access-group' command. Extended ACLs cannot filter based on MAC addresses; that is done by MAC ACLs. They are not limited to source-only filtering.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Extended ACLs can filter based on source and destination IP addresses.
Why this is correct
Correct because extended ACLs evaluate both source and destination addresses.
Related concept
Static NAT maps one inside address to one outside address.
✓
Extended ACLs can filter based on TCP or UDP port numbers.
Why this is correct
Correct because extended ACLs can specify protocol and port information for TCP/UDP.
Related concept
Static NAT maps one inside address to one outside address.
✓
Extended ACLs are processed in order until a matching permit or deny statement is found.
Why this is correct
Correct because ACLs use first-match logic.
Related concept
Static NAT maps one inside address to one outside address.
✗
Extended ACLs can filter based on source MAC addresses.
Why it's wrong here
Incorrect because MAC address filtering is done by MAC ACLs, not IP extended ACLs.
✗
Extended ACLs only filter traffic based on the source IP address.
Why it's wrong here
Incorrect because extended ACLs can filter on both source and destination, as well as protocol and port.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 350-401 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
ACLs and CoPP — This question tests ACLs and CoPP — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Extended ACLs can filter based on source and destination IP addresses. — Extended ACLs can filter based on source and destination IP addresses, protocol, and port numbers. They are processed sequentially until a match is found, and an implicit deny any is at the end. They can be applied to interfaces using the 'ip access-group' command. Extended ACLs cannot filter based on MAC addresses; that is done by MAC ACLs. They are not limited to source-only filtering.
What should I do if I get this 350-401 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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