LFCS Networking Practice Question
Exhibit
Refer to the exhibit. [root@server ~]# ss -tln State Recv-Q Send-Q Local Address:Port Peer Address:Port LISTEN 0 128 0.0.0.0:22 0.0.0.0:* LISTEN 0 128 *:80 *:* LISTEN 0 128 *:443 *:* LISTEN 0 128 127.0.0.1:53 0.0.0.0:* LISTEN 0 128 0.0.0.0:8080 0.0.0.0:*
Based on the exhibit, which port is listening only on the loopback interface?
⚠ Common exam trap
Candidates often confuse 'listening on all interfaces' (0.0.0.0) with 'listening only on loopback' (127.0.0.1), and may incorrectly assume that common services like SSH or HTTP are loopback-only when they are typically bound to all interfaces.
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
✓
53
Port 53 (DNS) is configured to listen only on the loopback interface (127.0.0.1) as shown in the exhibit's output of `ss -tlnp`. The listening address `127.0.0.1:53` indicates the service is bound exclusively to the loopback interface, meaning it is not accessible from external network interfaces.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
53
Why this is correct
Listening on 127.0.0.1, which is the loopback interface only.
- ✗
22
Why it's wrong here
Listening on 0.0.0.0, meaning all interfaces.
- ✗
443
Why it's wrong here
Listening on * (all interfaces).
- ✗
80
Why it's wrong here
Listening on * (all interfaces).
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.