easyMultiple ChoiceObjective-mapped
XK0-006 Firewall (iptables) Practice Question
Exhibit
Refer to the exhibit. $ sudo iptables -L -n -v Chain INPUT (policy DROP 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 10 540 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443
A user can access a web server on this Linux system via HTTPS but cannot connect via SSH. Based on the exhibit, what is the most likely cause?
⚠ Common exam trap
Candidates often assume that because HTTPS works, SSH should also work. However, if the firewall has a default DROP policy, explicit allow rules are required for each service. The presence of an HTTPS rule does not imply SSH is allowed; each service must be explicitly permitted.
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
✓
The firewall is missing a rule to allow SSH traffic.
The exhibit likely shows that the INPUT chain has a default policy of DROP and contains an explicit rule to allow HTTPS (port 443) but no rule to allow SSH (port 22). With a default DROP policy, only traffic matching explicit allow rules passes. Since SSH traffic does not match any allow rule, it is dropped, preventing SSH connections while HTTPS (with an explicit rule) works. Therefore, the most likely cause is that the firewall is missing a rule to allow SSH traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The SSH service is not running.
Why it's wrong here
The exhibit does not indicate the status of the SSH service.
- ✗
The eth0 interface is down.
Why it's wrong here
The exhibit shows packets being counted on eth0 for HTTPS, so the interface is up.
- ✓
The firewall is missing a rule to allow SSH traffic.
Why this is correct
Only HTTPS is allowed; SSH packets are dropped by the default DROP policy.
- ✗
The INPUT chain default policy is DROP.
Why it's wrong here
While true, the root cause is the absence of an SSH ACCEPT rule; the default policy would not affect SSH if an allow rule existed.
Go deeper
Related to this question
Learn chapter
Linux Fundamentals and History
Key term
Policy
A policy is a set of rules or guidelines that defines how an organization manages, secures, and operates its IT systems and services.
Key term
User
A user is any person, system, or device that interacts with an IT service, resource, or identity system, typically authenticated through credentials and authorized to perform specific actions.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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