The correct conclusion is that Telnet traffic from any source is denied. This is because the ACL 101 processes entries sequentially: the first line permits HTTP from the 192.168.1.0/24 subnet, the second line explicitly denies TCP traffic to port 23 (Telnet) from any source, and the third line permits all other IP traffic. The match counters confirm that 50 Telnet attempts have been blocked, while HTTP and general traffic have been allowed. On the ENCOR 350-401 exam, this tests your ability to read ACL output and understand implicit deny logic—a common trap is forgetting that the order of entries matters, and that a deny entry for a specific protocol overrides a later permit all. Remember the memory tip: "ACLs are like bouncers—they check the list in order, and once a rule matches, the action sticks."
CCNP Infrastructure Security Practice Question
This 350-401 practice question tests your understanding of infrastructure security. 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 101
Extended IP access list 101
10 permit tcp 192.168.1.0 0.0.0.255 any eq 80 (100 matches)
20 deny tcp any any eq 23 (50 matches)
30 permit ip any any (200 matches)
Why wrong: The first entry only permits HTTP, not Telnet. The second entry denies Telnet from any source, including 192.168.1.0/24.
B
Telnet traffic from any source is denied.
Entry 20 denies TCP port 23 (Telnet) from any source to any destination.
C
HTTP traffic from any source is permitted.
Why wrong: HTTP is only permitted from 192.168.1.0/24, not from any source.
D
All traffic is permitted because of the last entry.
Why wrong: The last entry permits all IP traffic, but Telnet is still denied because ACLs are processed sequentially and the deny entry is hit first for Telnet.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Telnet traffic from any source is denied.
The ACL 101 has three entries. The first permits HTTP traffic from 192.168.1.0/24 to any destination. The second denies Telnet traffic from any source. The third permits all other IP traffic. The match counters show hits. Since Telnet is denied, any Telnet attempt will be blocked unless it matches a preceding permit (which it doesn't).
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Telnet traffic from 192.168.1.0/24 is permitted.
Why it's wrong here
The first entry only permits HTTP, not Telnet. The second entry denies Telnet from any source, including 192.168.1.0/24.
✓
Telnet traffic from any source is denied.
Why this is correct
Entry 20 denies TCP port 23 (Telnet) from any source to any destination.
Related concept
Static NAT maps one inside address to one outside address.
✗
HTTP traffic from any source is permitted.
Why it's wrong here
HTTP is only permitted from 192.168.1.0/24, not from any source.
✗
All traffic is permitted because of the last entry.
Why it's wrong here
The last entry permits all IP traffic, but Telnet is still denied because ACLs are processed sequentially and the deny entry is hit first for Telnet.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
Infrastructure Security — This question tests Infrastructure Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Telnet traffic from any source is denied. — The ACL 101 has three entries. The first permits HTTP traffic from 192.168.1.0/24 to any destination. The second denies Telnet traffic from any source. The third permits all other IP traffic. The match counters show hits. Since Telnet is denied, any Telnet attempt will be blocked unless it matches a preceding permit (which it doesn't).
What should I do if I get this 350-401 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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