easyMultiple ChoiceObjective-mapped
ISC2 CC Practice Question: A network administrator configures the ACL on a…
Exhibit
Refer to the exhibit. ``` interface GigabitEthernet0/1 ip access-group BLOCK_TELNET in ! ip access-list extended BLOCK_TELNET deny tcp any any eq 23 permit ip any any ```
A network administrator configures the ACL on a router as shown. What is the effect of this access list?
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
✓
Blocks Telnet traffic entering the interface, but allows all other traffic
The ACL denies TCP traffic to port 23 (Telnet) and permits all other IP traffic. Option B is wrong because SSH is port 22. Option C is wrong because the ACL is applied inbound on Gig0/1, so it filters incoming traffic only, not outgoing. Option D is wrong because it applies to all TCP traffic, not just Telnet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Blocks Telnet traffic entering the interface, but allows all other traffic
Why this is correct
The deny statement blocks port 23 (Telnet), and the permit any permits everything else.
- ✗
Blocks SSH traffic (port 22) from entering the interface
Why it's wrong here
SSH uses port 22, which is not blocked.
- ✗
Blocks Telnet traffic leaving the interface, but allows all other traffic
Why it's wrong here
The ACL is applied inbound (in), so it filters incoming traffic.
- ✗
Blocks all TCP traffic except Telnet
Why it's wrong here
It denies only Telnet (port 23) and permits all other TCP and IP traffic.
Visual reference
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Related to this question
Learn chapter
Access Control Fundamentals
Key term
TCP
TCP is a connection-oriented transport layer protocol that ensures reliable, ordered, and error-checked delivery of data between applications over IP networks.
Key term
Telnet
Telnet is a network protocol that provides a bidirectional, interactive text-based communication session between two machines over a network, typically used for remote access and management of network devices.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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