Question 1mediummulti select
Full question →mediummulti selectObjective-mapped
Which two statements accurately describe ACL behavior on Cisco devices?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
ACL entries are processed from top to bottom until a match is found.
This is correct because Cisco ACLs are evaluated sequentially and stop at the first match.
B
Best answer
ACLs end with an implicit deny if unmatched traffic reaches the end.
This is correct because unmatched traffic is denied by default at the end of the ACL.
C
Distractor review
ACLs always evaluate every line before deciding the action.
This is wrong because ACLs stop processing at the first match.
D
Distractor review
ACLs end with an implicit permit unless configured otherwise.
This is wrong because Cisco ACLs end with an implicit deny.
E
Distractor review
ACLs apply only to Layer 1 traffic and not IP packets.
This is wrong because ACLs commonly filter Layer 3 and Layer 4 traffic characteristics.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that ACLs evaluate every line before deciding to permit or deny traffic. Candidates might think that if no explicit deny exists, traffic is allowed by default. However, Cisco ACLs stop processing at the first match, and if no match occurs, the implicit deny at the end blocks the traffic. This misunderstanding can lead to incorrect answers about ACL behavior and cause misconfigurations in real networks. Remembering that ACLs use a “first match wins” approach and end with an implicit deny helps avoid this trap.
Technical deep dive
How to think about this question
Access Control Lists (ACLs) on Cisco devices are fundamental security tools used to filter network traffic based on defined criteria such as source and destination IP addresses, protocols, and ports. ACLs operate primarily at Layer 3 (Network Layer) and Layer 4 (Transport Layer), enabling granular control over which packets are permitted or denied through interfaces. The core concept behind ACL processing is that each ACL consists of multiple entries or statements, each specifying a condition and an action (permit or deny). When a packet arrives at an interface where an ACL is applied, the device evaluates the ACL entries sequentially from the top down. The evaluation stops immediately when a match is found, and the corresponding action is taken. If no entries match the packet, the ACL implicitly denies the packet at the end, even if no explicit deny statement exists. This implicit deny rule is a critical security feature that prevents unintended traffic from passing through. A common exam trap involves misunderstanding the implicit deny behavior or assuming ACLs evaluate all entries before deciding. Some candidates mistakenly believe ACLs permit unmatched traffic by default or that all lines are checked before a decision. In practice, the first matching entry determines the fate of the packet, and unmatched packets are denied implicitly. This behavior ensures predictable and secure filtering but requires careful ordering of ACL entries to avoid unintended traffic blocking or permitting.
KKey Concepts to Remember
- ACL entries on Cisco devices are processed sequentially from top to bottom until a matching condition is found.
- Cisco ACLs have an implicit deny at the end that blocks any traffic not explicitly permitted by earlier entries.
- The first matching ACL entry determines whether a packet is permitted or denied, preventing further evaluation of subsequent lines.
- ACLs filter traffic primarily at Layer 3 and Layer 4, using IP addresses, protocols, and port numbers as matching criteria.
- Explicit deny statements in ACLs are optional because unmatched traffic is denied by default due to the implicit deny rule.
- Ordering of ACL entries is critical because once a match occurs, no further ACL lines are evaluated for that packet.
- Misunderstanding the implicit deny or the sequential processing of ACLs is a common source of configuration errors and exam mistakes.
- ACLs do not operate at Layer 1; they control packet flow based on network and transport layer information.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
ACL entries on Cisco devices are processed sequentially from top to bottom until a matching condition is found.
What is the correct answer to this question?
The correct answer is: ACL entries are processed from top to bottom until a match is found. — ACL questions often depend on understanding how Cisco devices process entries line by line. In plain language, ACL entries are evaluated from top to bottom, and the first matching statement decides the result. If traffic reaches the end without matching a permit, it is denied by the implicit deny. These two ideas explain many real ACL troubleshooting cases. The wrong answers often sound plausible because they borrow language from other parts of networking. But ACLs do not normally evaluate all lines before choosing, and they do not end with an implicit permit. Once you remember “first match wins” and “implicit deny at the end,” many access-list questions become much easier.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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