Question 2,090 of 2,152
IPv4 Access Control ListsmediumMultiple ChoiceObjective-mapped

300-410 IPv4 Access Control Lists Practice Question

This 300-410 practice question tests your understanding of ipv4 access control lists. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.

A network engineer runs the following command on Router R1:

R1# show ip access-lists

Extended IP access list 120

10 permit tcp 10.0.0.0 0.255.255.255 any eq www (1000 matches)
    
20 permit udp any any eq dns (500 matches)
    
30 deny ip any any (200 matches)

Based on this output, what is the problem?

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

The ACL is blocking all traffic except web and DNS, which may be too restrictive.

Option B is correct because the ACL explicitly permits only TCP port 80 (www) and UDP port 53 (dns) traffic, while the final deny ip any any statement blocks all other traffic. With only 1000 matches for web and 500 for DNS, the ACL is likely too restrictive for a production network, as it would drop essential traffic such as routing protocols, management traffic (e.g., SSH, SNMP), or other application flows. The output shows the ACL is present and has hit counts, but its restrictive nature is the problem.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The ACL is correctly permitting web and DNS traffic.

    Why it's wrong here

    While it permits those, the deny all statement may block other needed traffic.

  • The ACL is blocking all traffic except web and DNS, which may be too restrictive.

    Why this is correct

    The deny ip any any with matches shows that other traffic is being denied, which could be a problem.

    Related concept

    Read the scenario before looking for a memorised answer.

  • The ACL has no effect because it is not applied.

    Why it's wrong here

    The match counts indicate the ACL is applied and active.

  • The ACL allows all traffic because of the permit statements.

    Why it's wrong here

    The deny ip any any overrides and denies all other traffic.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that an ACL with permit statements is automatically 'correct' or 'permissive,' when in fact the explicit deny at the end makes it highly restrictive, and candidates may overlook the need to evaluate whether the ACL matches the intended security policy.

Detailed technical explanation

How to think about this question

Cisco ACLs process entries sequentially from top to bottom; once a match occurs, no further lines are evaluated. The implicit deny ip any any at the end of every ACL is overridden here by the explicit deny statement, but the behavior is identical. In real-world scenarios, an ACL that only permits web and DNS would break services like VoIP, NTP, or ICMP (ping), which are often required for network health and troubleshooting.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

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

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

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.

Visual reference

Source Router + ACL permit 10.0.0.0/8 deny any Server 10.0.0.5 ✓ 192.168.1.1 ✗ dropped ACLs evaluate top-down; first match wins — implicit deny all at end

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

Got this wrong? Here's your next step.

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FAQ

Questions learners often ask

What does this 300-410 question test?

IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The ACL is blocking all traffic except web and DNS, which may be too restrictive. — Option B is correct because the ACL explicitly permits only TCP port 80 (www) and UDP port 53 (dns) traffic, while the final deny ip any any statement blocks all other traffic. With only 1000 matches for web and 500 for DNS, the ACL is likely too restrictive for a production network, as it would drop essential traffic such as routing protocols, management traffic (e.g., SSH, SNMP), or other application flows. The output shows the ACL is present and has hit counts, but its restrictive nature is the problem.

What should I do if I get this 300-410 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 24, 2026

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