CCNA Network Services and Security Practice Question
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?
⚠ Common exam trap
Do not confuse the capabilities of standard ACLs with those of extended ACLs. Remember, standard ACLs filter only by source IP.
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
✓
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.
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
Standard ACLs filter on source address only, so they cannot separate Telnet from SSH because both protocols originate from the same subnet. Distinguishing them requires extended ACL syntax matching TCP port 23 versus 22, which is the constraint the policy demands.
- ✗
Because standard ACLs are valid only on wireless networks.
Why it's wrong here
Standard ACLs operate on any routed interface, wired or wireless, so this claim is factually wrong. They are tempting because they are simple source-only filters, useful for coarse permit-or-deny by subnet; here the requirement needs destination port matching, which only extended ACLs provide.
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
Telnet uses TCP port 23 and SSH port 22, so they are distinguishable by destination port. A standard ACL filters only on source address, so it cannot separate the two protocols from one subnet; an extended ACL, matching destination port, is the correct tool for this requirement.
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
ACLs filter on TCP/UDP port numbers, so SSH (TCP 22) is filterable; the real limitation is that standard ACLs match only source addresses, so a single subnet entry cannot separate Telnet from SSH. It is tempting because extended ACLs are the usual tool for port-based filtering.
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
Standard ACLs filter on source address only, so they cannot separate Telnet from SSH because both protocols originate from the same subnet. Distinguishing them requires extended ACL syntax matching TCP port 23 versus 22, which is the constraint the policy demands.
✗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?”
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Related to this question
Learn chapter
Network Automation Benefits
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
Key term
ACL
An Access Control List is a set of rules that determines who or what can access specific network resources or data.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.