This LFCS practice question tests your understanding of networking. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Exhibit
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
Refer to the exhibit. The output of 'ip addr show' reveals that eth0 is in state DOWN and has no IPv4 address. Which command is most likely to bring the interface up and obtain an IP via DHCP?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ifup eth0
Option B is correct because the `ifup` command is a distribution-agnostic tool that reads the interface configuration from files (e.g., `/etc/network/interfaces` on Debian/Ubuntu or `/etc/sysconfig/network-scripts/ifcfg-eth0` on RHEL/CentOS) and brings the interface up while automatically initiating a DHCP client (e.g., dhclient or dhcpcd) to obtain an IPv4 address. This is the standard way to activate a network interface with its configured addressing method, including DHCP, in a single step.
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.
✗
ip link set eth0 up
Why it's wrong here
Brings the interface up but DHCP may not automatically start unless configured.
✓
ifup eth0
Why this is correct
ifup invokes the network configuration scripts, which will start DHCP based on config.
Clue confirmation
The clue words "most likely", "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
ip route add default via 192.168.1.1 dev eth0
Why it's wrong here
Adds a default route but does not bring the interface up or obtain an address.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume `ip link set eth0 up` (options A or D) is sufficient to obtain an IP via DHCP, but this command only activates the link layer and does not invoke any DHCP client, leaving the interface without an IP address.
Detailed technical explanation
How to think about this question
Under the hood, `ifup` parses the interface configuration file to determine the addressing method (e.g., 'dhcp' or 'static') and then executes the appropriate sequence of commands: it sets the link up via `ip link set`, then runs a DHCP client (like dhclient) which performs a four-step DORA (Discover, Offer, Request, Acknowledge) exchange to lease an IP address. A subtle behavior is that `ifup` may also apply any custom pre-up or post-up scripts defined in the configuration, making it more robust than manually running `ip link set` alone.
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 LFCS 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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ifup eth0 — Option B is correct because the `ifup` command is a distribution-agnostic tool that reads the interface configuration from files (e.g., `/etc/network/interfaces` on Debian/Ubuntu or `/etc/sysconfig/network-scripts/ifcfg-eth0` on RHEL/CentOS) and brings the interface up while automatically initiating a DHCP client (e.g., dhclient or dhcpcd) to obtain an IPv4 address. This is the standard way to activate a network interface with its configured addressing method, including DHCP, in a single step.
What should I do if I get this LFCS 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: "most likely", "which command". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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