The correct interpretation is that the IPv6 binding table shows three distinct states—REACH, STALE, and INCOMP—each reflecting a different phase of Neighbor Discovery (ND) learning and policy enforcement. The REACH entry on Fa0/1 with a TRUSTED policy indicates an actively verified neighbor with confirmed bidirectional reachability, while the STALE entry on Fa0/0 with an INSPECT policy means the neighbor was once reachable but hasn’t been confirmed within the last 30 seconds, so it remains usable but requires re-validation before forwarding. The INCOMP entry with no policy and a zero age shows an incomplete ND resolution, where a solicitation was sent but no advertisement has been received yet. On the Cisco CCNP ENARSI 300-410 exam, this command tests your ability to read the IPv6 First Hop Security binding table, often used in scenarios involving RA Guard, DHCPv6 Guard, or Source Guard. A common trap is assuming STALE means unreachable—it does not; the entry is still valid until the neighbor cache timeout expires. Memory tip: think of REACH as “ready and confirmed,” STALE as “still standing but needs a handshake,” and INCOMP as “incomplete—still waiting for a reply.”
300-410 IPv6 First Hop Security Practice Question
This 300-410 practice question tests your understanding of ipv6 first hop security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 network engineer runs the following command to verify IPv6 binding table:
R1# show ipv6 neighbors binding
IPv6 Address Age Link-layer Addr State Interface VLAN Policy
2001:db8::1 10 0011.2233.4455 REACH Fa0/1 10 TRUSTED
2001:db8::2 5 00aa.bbcc.ddee STALE Fa0/0 10 INSPECT
2001:db8::3 0 1111.2222.3333 INCOMP Fa0/0 10 -
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The binding table shows three entries: one reachable on trusted port, one stale on untrusted port, and one incomplete, indicating active ND learning.
The show command displays the IPv6 binding table with entries learned via ND. The table shows reachable, stale, and incomplete entries with associated policies.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 binding table shows three entries: one reachable on trusted port, one stale on untrusted port, and one incomplete, indicating active ND learning.
Why this is correct
The output correctly shows the state and policy for each entry.
The binding table is empty, indicating no ND activity.
Why it's wrong here
There are three entries, so it is not empty.
✗
The binding table shows all entries as reachable, indicating stable neighbor relationships.
Why it's wrong here
One entry is STALE and one is INCOMP, not all reachable.
✗
The binding table is only for DHCPv6-learned addresses.
Why it's wrong here
The table includes ND-learned addresses, not just DHCPv6.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
IPv6 First Hop Security — This question tests IPv6 First Hop Security — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The binding table shows three entries: one reachable on trusted port, one stale on untrusted port, and one incomplete, indicating active ND learning. — The show command displays the IPv6 binding table with entries learned via ND. The table shows reachable, stale, and incomplete entries with associated policies.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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