This LPIC-2 practice question tests your understanding of advanced networking configuration. 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.
An administrator is troubleshooting IPv6 connectivity on a Linux host. The host has an IPv6 address configured on eth0, but cannot ping6 the default gateway. The output of 'ip -6 route show' shows a default route via fe80::1 dev eth0. Which tool should be used to verify that the neighbor discovery process is working?
tcpdump -i eth0 icmp6
Why wrong: While this can capture neighbor solicitation/advertisements, it is not a quick verification tool.
traceroute6
Why wrong: traceroute6 tests path, but not neighbor discovery for the first hop.
ip neigh show
This shows the neighbor discovery cache, including unresolved entries.
ndp -n
Why wrong: ndp is a FreeBSD command, not available on Linux.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ip neigh show
The 'ip neigh show' command displays the neighbor cache (equivalent to ARP table for IPv6), which is populated by the Neighbor Discovery Protocol (NDP). Since the default gateway is a link-local address (fe80::1), the host must have resolved the gateway's MAC address via NDP before it can send packets. If the neighbor entry is missing or incomplete (e.g., STALE or FAILED), it indicates that the neighbor discovery process is not working, which would explain the ping failure.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
tcpdump -i eth0 icmp6
Why it's wrong here
While this can capture neighbor solicitation/advertisements, it is not a quick verification tool.
traceroute6
Why it's wrong here
traceroute6 tests path, but not neighbor discovery for the first hop.
ip neigh show
Why this is correct
This shows the neighbor discovery cache, including unresolved entries.
Related concept
Read the scenario before looking for a memorised answer.
ndp -n
Why it's wrong here
ndp is a FreeBSD command, not available on Linux.
Common exam traps
The trap here is that candidates confuse the Linux command 'ip neigh show' with the BSD command 'ndp -n', or they think that packet capture (tcpdump) is the only way to diagnose NDP issues, when in fact the neighbor cache provides a direct snapshot of the resolution state.
Trap categories for this question
Command / output trap
ndp is a FreeBSD command, not available on Linux.
Detailed technical explanation
Neighbor Discovery Protocol (NDP) uses ICMPv6 types 135 (Neighbor Solicitation) and 136 (Neighbor Advertisement) to resolve MAC addresses from IPv6 addresses. The neighbor cache stores these mappings with states such as REACHABLE, STALE, DELAY, or PROBE; a missing or FAILED entry indicates that NDP resolution failed, often due to a missing or misconfigured link-local gateway. In real-world scenarios, a common cause is that the gateway's MAC address changed (e.g., after a router reboot) and the neighbor cache is stale, requiring manual clearing with 'ip neigh flush'.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Advanced Networking Configuration — study guide chapter
Learn the concepts, then practise the questions
Advanced Networking Configuration practice questions
Targeted practice on this topic area only
All LPIC-2 questions
511 questions across all exam domains
Linux Professional Institute Certification Level 2 LPIC-2 study guide
Full concept coverage aligned to exam objectives
LPIC-2 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise LPIC-2 questions linked to Linux Kernel and System Startup.
Practise LPIC-2 questions linked to Block Devices, Filesystems and Advanced Storage.
Practise LPIC-2 questions linked to Advanced Networking Configuration.
Practise LPIC-2 questions linked to DNS, Web and Mail Services.
Practise LPIC-2 questions linked to File Sharing and Samba.
Practise LPIC-2 questions linked to System Security.
Practise LPIC-2 questions linked to Network Client Management.
Practise LPIC-2 questions linked to LPIC-2 fundamentals.
Practise LPIC-2 questions linked to LPIC-2 scenario.
Practise LPIC-2 questions linked to LPIC-2 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Advanced Networking Configuration — This question tests Advanced Networking Configuration — Read the scenario before looking for a memorised answer..
The correct answer is: ip neigh show — The 'ip neigh show' command displays the neighbor cache (equivalent to ARP table for IPv6), which is populated by the Neighbor Discovery Protocol (NDP). Since the default gateway is a link-local address (fe80::1), the host must have resolved the gateway's MAC address via NDP before it can send packets. If the neighbor entry is missing or incomplete (e.g., STALE or FAILED), it indicates that the neighbor discovery process is not working, which would explain the ping failure.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 25, 2026
This LPIC-2 practice question is part of Courseiva's free LPI 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 LPIC-2 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.