The answer is `firewall-cmd --add-port=8080/tcp --permanent`. This command is correct because it explicitly opens TCP port 8080 in firewalld, the default dynamic firewall daemon on RHEL/CentOS 8/9, and the `--permanent` flag ensures the rule survives a reboot. When a web server is running but clients cannot connect, the firewall is almost always the culprit—it blocks inbound traffic by default, so you must use `--add-port` with the protocol (`tcp`) to allow connections on that specific port. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of firewalld’s runtime versus permanent rules; a common trap is forgetting `--permanent` or omitting the protocol suffix, which causes the command to fail silently. Remember the mnemonic “APT” for **A**dd **P**ort **T**CP—always specify the protocol and make it permanent to lock in the change.
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Network Topology
A web server is running on the system but clients cannot connect to port 8080. Based on the exhibit, which command should the administrator run to allow traffic on port 8080?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
firewall-cmd --add-rich-rule='rule port port=8080 protocol=tcp accept' --permanent
Why wrong: While a rich rule could also work, the standard and simpler approach is to add the port directly. The rich rule is more complex and not the most straightforward solution.
B
firewall-cmd --add-port=8080/tcp --permanent
This command adds TCP port 8080 permanently to the firewall rules, which is required for HTTPS on a non-standard port.
C
firewall-cmd --add-port=8080/udp --permanent
Why wrong: Web traffic uses TCP, not UDP; opening UDP port 8080 would not help.
D
firewall-cmd --add-service=http --permanent
Why wrong: Adding service 'http' only opens port 80, not port 8080.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
firewall-cmd --add-port=8080/tcp --permanent
The correct command is `firewall-cmd --add-port=8080/tcp --permanent` because it opens TCP port 8080 in firewalld, which is the default firewall management tool on RHEL/CentOS 8/9. Since the web server is running but clients cannot connect, the firewall is likely blocking inbound traffic on that port. The `--add-port` option with the `tcp` protocol explicitly allows TCP connections, and `--permanent` makes the rule persist across reboots.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
firewall-cmd --add-rich-rule='rule port port=8080 protocol=tcp accept' --permanent
Why it's wrong here
While a rich rule could also work, the standard and simpler approach is to add the port directly. The rich rule is more complex and not the most straightforward solution.
✓
firewall-cmd --add-port=8080/tcp --permanent
Why this is correct
This command adds TCP port 8080 permanently to the firewall rules, which is required for HTTPS on a non-standard port.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
firewall-cmd --add-port=8080/udp --permanent
Why it's wrong here
Web traffic uses TCP, not UDP; opening UDP port 8080 would not help.
✗
firewall-cmd --add-service=http --permanent
Why it's wrong here
Adding service 'http' only opens port 80, not port 8080.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse `--add-port` with `--add-service` or use the wrong protocol (UDP instead of TCP), or incorrectly format a rich rule, because the exam tests precise syntax and the distinction between service-based and port-based rules in firewalld.
Detailed technical explanation
How to think about this question
Firewalld uses zones and services to manage rules; `--add-port` directly opens a specific port/protocol combination, while `--add-service` maps to predefined port definitions in `/usr/lib/firewalld/services/`. The `--permanent` flag writes the rule to the XML configuration files (e.g., `/etc/firewalld/zones/public.xml`), but the rule only takes effect after a `firewall-cmd --reload` or service restart unless `--runtime-to-permanent` is used. In real-world scenarios, administrators often forget to reload the firewall after adding permanent rules, causing the rule to not apply until the next reboot.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the XK0-005 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: firewall-cmd --add-port=8080/tcp --permanent — The correct command is `firewall-cmd --add-port=8080/tcp --permanent` because it opens TCP port 8080 in firewalld, which is the default firewall management tool on RHEL/CentOS 8/9. Since the web server is running but clients cannot connect, the firewall is likely blocking inbound traffic on that port. The `--add-port` option with the `tcp` protocol explicitly allows TCP connections, and `--permanent` makes the rule persist across reboots.
What should I do if I get this XK0-005 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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