The answer is that the client's firewall is blocking incoming ICMP echo requests. This is correct because the client can successfully ping the lab server at 192.168.100.50, proving that outbound traffic and the routing table are configured properly—the direct route to 192.168.100.0/24 via eth1 is present and functional. However, when the server tries to ping the client, the ICMP echo request is an inbound connection attempt, and a firewall like iptables or ufw on the Linux client is likely dropping these packets by default while still allowing outbound traffic. On the LPIC-2 exam, this scenario tests your understanding of asymmetric routing and stateful firewall behavior, often appearing as a trap where candidates mistakenly blame routing tables or DHCP misconfiguration. A common memory tip is "ping is a two-way street: outbound success doesn't guarantee inbound return"—always check firewall rules for incoming ICMP when the reverse ping fails.
LPIC-2 Network Client Management Practice Question
This LPIC-2 practice question tests your understanding of network client management. 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.
A company has a Linux client running Ubuntu 20.04 that is used by multiple developers. The client has two network interfaces: eth0 (connected to the corporate network with DHCP) and eth1 (connected to a test lab with static IP 192.168.100.10/24). The client needs to access both the internet (via eth0) and the lab network (192.168.100.0/24). The default gateway is 10.0.0.1 on eth0. The lab network has a server at 192.168.100.50 that provides DHCP for the lab devices, but the client's eth1 is statically configured. Recently, the client cannot reach the lab server at 192.168.100.50. The administrator checks the routing table and sees:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.0.0.1 0.0.0.0 UG 100 0 0 eth0
10.0.0.0 0.0.0.0 255.255.255.0 U 100 0 0 eth0
192.168.100.0 0.0.0.0 255.255.255.0 U 100 0 0 eth1
The administrator can ping 192.168.100.50 from the client. However, the lab server cannot ping the client. What is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The client's firewall is blocking incoming ICMP echo requests.
The client can ping the lab server (192.168.100.50), proving that outbound traffic from the client to the lab network works correctly. However, the lab server cannot ping the client, which indicates that either the return traffic is blocked or the client does not have a route back to the server. Since the client's routing table shows a direct route to 192.168.100.0/24 via eth1, the issue is not a missing route; instead, the most likely cause is that the client's firewall (e.g., iptables or ufw) is blocking incoming ICMP Echo Requests (ping) on eth1, while allowing outbound traffic.
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.
✗
The lab server's default gateway is misconfigured.
Why it's wrong here
The lab server's default gateway does not affect direct communication within the same subnet.
✓
The client's firewall is blocking incoming ICMP echo requests.
Why this is correct
The client can initiate traffic but may block incoming connections, preventing the server from pinging back.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The client has no route to the lab subnet.
Why it's wrong here
The routing table shows a route to 192.168.100.0/24 via eth1.
✗
The client's default gateway is misconfigured.
Why it's wrong here
The default gateway is correctly set to 10.0.0.1 for internet access; lab traffic is local.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a successful ping from client to server implies full bidirectional connectivity, but they overlook that firewalls often block inbound ICMP while permitting outbound, leading to a one-way communication failure.
Trap categories for this question
Command / output trap
The routing table shows a route to 192.168.100.0/24 via eth1.
Detailed technical explanation
How to think about this question
When a client on the same subnet cannot be pinged, the problem often lies in the host firewall (e.g., iptables rules that drop INPUT packets by default) or in the ARP resolution if the client does not respond to ARP requests. In Ubuntu 20.04, ufw (Uncomplicated Firewall) may be enabled and blocking incoming ICMP, while the default iptables policy for the INPUT chain is DROP. A common real-world scenario is that developers configure static IPs but forget to allow ICMP on the interface, causing asymmetric routing issues where outbound traffic works but inbound is silently dropped.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
Network Client Management — This question tests Network Client Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The client's firewall is blocking incoming ICMP echo requests. — The client can ping the lab server (192.168.100.50), proving that outbound traffic from the client to the lab network works correctly. However, the lab server cannot ping the client, which indicates that either the return traffic is blocked or the client does not have a route back to the server. Since the client's routing table shows a direct route to 192.168.100.0/24 via eth1, the issue is not a missing route; instead, the most likely cause is that the client's firewall (e.g., iptables or ufw) is blocking incoming ICMP Echo Requests (ping) on eth1, while allowing outbound traffic.
What should I do if I get this LPIC-2 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". 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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Question Discussion
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