Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
An administrator wants to prevent a specific subnet from using Telnet to reach network devices, while still allowing SSH from that same subnet. What is the strongest reason a standard ACL is not enough by itself?
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
Because the policy must distinguish Telnet from SSH, which requires protocol or port-level matching.
This is correct because source-only matching cannot separate those two protocols.
B
Distractor review
Because standard ACLs are valid only on wireless networks.
This is wrong because standard ACLs are not wireless-only.
C
Distractor review
Because Telnet and SSH always use the same destination port.
This is wrong because they use different TCP ports.
D
Distractor review
Because SSH can never be filtered with ACLs.
This is wrong because SSH traffic can absolutely be filtered with ACL logic.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is believing that a standard ACL can block Telnet traffic while allowing SSH from the same subnet simply by filtering on source IP. This mistake ignores that standard ACLs do not inspect protocol or port information, so they cannot differentiate between Telnet and SSH. As a result, applying a standard ACL to block the subnet’s source IP would block both Telnet and SSH traffic indiscriminately, causing unintended access issues. Understanding this limitation prevents candidates from selecting incorrect answers based on incomplete ACL capabilities.
Technical deep dive
How to think about this question
Access Control Lists (ACLs) are fundamental tools in Cisco networking used to filter traffic based on defined criteria. Standard ACLs operate by filtering packets solely based on the source IP address, without inspecting the protocol or port information. This simplicity limits their use cases to broad filtering scenarios where only the source subnet or host matters. Extended ACLs, on the other hand, provide more detailed control by allowing matches on source and destination IP addresses, as well as Layer 4 protocol types and port numbers, enabling precise traffic filtering. In the context of differentiating Telnet and SSH traffic from the same subnet, the key distinction lies in their TCP destination ports: Telnet uses port 23, while SSH uses port 22. A standard ACL cannot differentiate between these because it does not evaluate port numbers or protocols; it only filters based on source IP. Therefore, to block Telnet traffic but permit SSH from the same subnet, an extended ACL is required to specify the destination port in the filtering rule. This capability ensures that only Telnet traffic is denied while SSH remains accessible. A common exam trap is assuming that source-based filtering with a standard ACL is sufficient to enforce protocol-specific policies. This mistake leads to overly broad blocking, potentially disrupting legitimate management access like SSH. In practical Cisco network deployments, administrators must understand that protocol and port-level filtering requires extended ACLs. Recognizing this distinction is essential for designing secure and functional access policies, especially when multiple protocols share the same source subnet but require different handling.
KKey Concepts to Remember
- A standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.
- Extended ACLs provide granular filtering by matching source and destination IP addresses, protocols, and TCP/UDP port numbers.
- Telnet and SSH use different TCP destination ports, with Telnet on port 23 and SSH on port 22, enabling protocol-level distinction.
- To block Telnet but allow SSH from the same subnet, an ACL must differentiate traffic by destination port, which standard ACLs cannot do.
- Cisco devices apply ACLs in a sequential order, stopping at the first match, so precise matching criteria are essential for correct filtering.
- Using only a standard ACL risks unintentionally blocking all traffic from the subnet, including allowed protocols like SSH.
- Extended ACLs enable network administrators to enforce security policies that depend on protocol and port distinctions within the same subnet.
- Understanding ACL types and their capabilities is critical for implementing effective access control in Cisco network environments.
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?
A standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.
What is the correct answer to this question?
The correct answer is: Because the policy must distinguish Telnet from SSH, which requires protocol or port-level matching. — A standard ACL is not enough by itself because the policy depends on distinguishing different protocols or destination ports, not just source address. In practical terms, the source subnet is the same for both Telnet and SSH. The ACL therefore needs to tell those two management protocols apart, which requires more granular matching than source-only logic. This is one of the clearest examples of why extended ACL capability matters.
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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