Quick Answer
The answer is 1000. Cisco IOS enforces a hard limit of 1000 entries in a single IPv4 ACL to prevent performance degradation and excessive memory consumption on the router, ensuring predictable forwarding behavior. This cap applies equally to standard, extended, and named ACLs, and it is a software-enforced boundary rather than a hardware limitation. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of ACL scalability and resource management; a common trap is assuming the limit is higher or that named ACLs have a different threshold. Remember that the limit is absolute—once you hit 1000 ACE lines, the router will reject additional entries. A simple memory tip: think of the "1" in 1000 as standing for "one single ACL," and the three zeros as a reminder that no extra entries are allowed beyond that triple-zero boundary.
This 300-410 practice question tests your understanding of ipv4 access control lists. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
What is the maximum number of entries that can be configured in a single IPv4 ACL in Cisco IOS?
1000
Cisco IOS generally supports up to 1000 ACEs per ACL, though hardware limits may be lower.
500
Why wrong: 500 is not the standard maximum; 1000 is more common.
Unlimited
Why wrong: There is a finite limit; unlimited is incorrect.
256
Why wrong: 256 is too low; the limit is higher.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
1000
Cisco IOS limits a single IPv4 ACL to a maximum of 1000 entries (ACE lines) to prevent performance degradation and excessive memory consumption on the router. This hard limit applies to both standard and extended numbered ACLs, as well as named ACLs, and is enforced by the software to ensure predictable forwarding behavior.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
1000
Why this is correct
Cisco IOS generally supports up to 1000 ACEs per ACL, though hardware limits may be lower.
Related concept
Read the scenario before looking for a memorised answer.
500
Why it's wrong here
500 is not the standard maximum; 1000 is more common.
Unlimited
Why it's wrong here
There is a finite limit; unlimited is incorrect.
256
Why it's wrong here
256 is too low; the limit is higher.
Common exam traps
Cisco often tests the 1000-entry limit to catch candidates who assume ACLs are unlimited or who confuse the limit with the 256-entry limit common on older Catalyst switch ACLs.
Detailed technical explanation
The 1000-entry limit is defined in Cisco IOS code and applies to both IPv4 and IPv6 ACLs, though IPv6 ACLs have a separate limit of 1000 entries as well. This restriction is not an RFC requirement but a Cisco implementation choice to balance granularity with hardware TCAM (Ternary Content-Addressable Memory) constraints; in practice, exceeding 1000 ACEs can cause high CPU utilization during ACL compilation and lookup, especially on older platforms. Real-world scenarios like large-scale BGP route filtering or complex security policies often require careful ACL design to stay within this limit, sometimes using object groups or prefix lists as alternatives.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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IPv4 Access Control Lists — study guide chapter
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FAQ
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
The correct answer is: 1000 — Cisco IOS limits a single IPv4 ACL to a maximum of 1000 entries (ACE lines) to prevent performance degradation and excessive memory consumption on the router. This hard limit applies to both standard and extended numbered ACLs, as well as named ACLs, and is enforced by the software to ensure predictable forwarding behavior.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
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