The answer is that a standard ACL is not enough by itself because the policy must distinguish Telnet from SSH, which requires protocol or port-level matching. Standard ACLs filter traffic based solely on the source IP address, but here the source subnet is identical for both Telnet and SSH traffic, making source-only logic useless for differentiating them. An extended ACL, by contrast, can match on the destination port (TCP 23 for Telnet, TCP 22 for SSH), allowing you to block Telnet while permitting SSH from the same subnet. On the CCNA 200-301 v2 exam, this scenario tests your understanding of ACL granularity and the fundamental limitation of standard ACLs—a common trap is assuming a standard ACL can handle protocol-specific filtering. Remember the memory tip: “Standard is source-only; extended is everything.”
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: a standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.. 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.
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
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.
Key principle: A standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Because the policy must distinguish Telnet from SSH, which requires protocol or port-level matching.
Why this is correct
This is correct because source-only matching cannot separate those two protocols.
Related concept
A standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.
✗
Because standard ACLs are valid only on wireless networks.
Why it's wrong here
This is wrong because standard ACLs are not wireless-only.
When this WOULD be correct
If a question stated that standard ACLs are only applicable to wireless networks and asked about their limitations in that context, then this option would be correct. For example, a scenario where a candidate must choose the best ACL type for a wireless-only environment would validate this statement.
✗
Because Telnet and SSH always use the same destination port.
Why it's wrong here
This is wrong because they use different TCP ports.
When this WOULD be correct
If a question stated that both Telnet and SSH were configured to use the same port due to a specific network policy or misconfiguration, then this option could be correct, as it would imply that distinguishing between them would be impossible.
✗
Because SSH can never be filtered with ACLs.
Why it's wrong here
This is wrong because SSH traffic can absolutely be filtered with ACL logic.
When this WOULD be correct
In a different exam scenario, if the question stated that SSH traffic is inherently unfilterable due to its encryption or that it operates on a unique protocol not recognized by ACLs, then this option could be correct. For example, a question could ask about filtering protocols that are not supported by ACLs.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Because the policy must distinguish Telnet from SSH, which requires protocol or port-level matching.Correct answer▾
Why this is correct
This is correct because source-only matching cannot separate those two protocols.
✗Because standard ACLs are valid only on wireless networks.Wrong answer — click to see why▾
Why this is wrong here
Standard ACLs are not limited to wireless networks; they can be applied to any interface on a router, including wired connections. This option misrepresents the applicability of standard ACLs.
★ When this WOULD be the correct answer
If a question stated that standard ACLs are only applicable to wireless networks and asked about their limitations in that context, then this option would be correct. For example, a scenario where a candidate must choose the best ACL type for a wireless-only environment would validate this statement.
Why candidates choose this
Candidates may confuse the specific use cases of ACLs with network types, leading them to believe that standard ACLs have restrictions based on the type of network, rather than understanding their broader applicability.
✗Because Telnet and SSH always use the same destination port.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because Telnet and SSH use different destination ports; Telnet typically uses port 23, while SSH uses port 22, allowing for distinct filtering in ACLs.
★ When this WOULD be the correct answer
If a question stated that both Telnet and SSH were configured to use the same port due to a specific network policy or misconfiguration, then this option could be correct, as it would imply that distinguishing between them would be impossible.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of port assignments and the assumption that both protocols operate on the same layer, leading to confusion about their distinct characteristics.
✗Because SSH can never be filtered with ACLs.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because SSH can indeed be filtered using ACLs, as they can match traffic based on IP addresses and protocols. Standard ACLs can be applied to control SSH traffic just like any other traffic type.
★ When this WOULD be the correct answer
In a different exam scenario, if the question stated that SSH traffic is inherently unfilterable due to its encryption or that it operates on a unique protocol not recognized by ACLs, then this option could be correct. For example, a question could ask about filtering protocols that are not supported by ACLs.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of ACL capabilities, believing that the complexity of SSH encryption prevents any form of filtering, thus making it seem like a plausible answer.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Do not confuse the capabilities of standard ACLs with those of extended ACLs. Remember, standard ACLs filter only by source IP.
Detailed technical explanation
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.
Key takeaway
A standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.
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 200-301 question in full detail.
Review a standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — 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?
Review a standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
A standard ACL filters traffic based solely on source IP addresses without considering protocol types or port numbers.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An administrator wants to permit HTTP and HTTPS from 10.1.10.0/24 to a web server at 198.51.100.20 and deny everything else from that subnet. Which ACL type is required?
hard
A.Named standard ACL
✓ B.Extended ACL
C.Prefix list
D.MAC access-list
Why B: A standard ACL can match only the source address. To permit specific protocols and ports such as TCP 80 and 443 to a specific destination, the administrator must use an extended ACL.
Last reviewed: May 17, 2026
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