The answer is that the static binding must be associated with a valid ND entry; without an NA from the host, the binding remains in an INCOMPLETE state. IPv6 Source Guard with `ipv6 verify source` relies on the binding table to validate source addresses, and even a manually configured `ipv6 neighbor binding` entry will not be used for forwarding unless the switch has a corresponding ND cache entry in the REACHABLE state. This is because the binding table entry is tied to the ND process—if the host never sends an unsolicited Neighbor Advertisement or the switch never receives a Router Solicitation to populate the ND cache, the binding stays incomplete and Source Guard drops the traffic. On the CCNP ENARSI 300-410 exam, this tests your understanding that static bindings do not automatically create ND entries; it is a common trap to assume a static binding alone is sufficient. Remember the memory tip: “Static binding needs an NA to play—no NA, no REACHABLE, no traffic.”
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.
An engineer configures IPv6 Source Guard on a switch port with 'ipv6 verify source' and also enables 'ipv6 snooping' globally. A legitimate host on that port is unable to send traffic, and the switch logs show that packets are being dropped due to source address validation failure. The host has a static IPv6 address and the engineer has configured a static binding using 'ipv6 neighbor binding' command. What is the most likely oversight?
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 static binding must be associated with a valid ND entry; without an NA from the host, the binding remains incomplete.
IPv6 Source Guard with 'ipv6 verify source' uses the binding table to validate source addresses. Even with a static binding, the binding table entry must be in the 'REACHABLE' state for Source Guard to accept traffic. If the static binding is configured but the switch does not have a corresponding ND entry (because the host never sends an NS or the switch does not learn it), the binding remains in 'INCOMPLETE' state and Source Guard drops the traffic. The edge case is that static bindings do not automatically populate the ND cache; the host must send an unsolicited NA or the switch must receive an RS to complete the binding.
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 static binding must be associated with a valid ND entry; without an NA from the host, the binding remains incomplete.
Why this is correct
Source Guard requires the binding to be in REACHABLE state, which requires ND activity.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The host must use DHCPv6 to obtain an address for Source Guard to work.
Why it's wrong here
Source Guard works with static addresses if bindings are present.
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 static binding must be associated with a valid ND entry; without an NA from the host, the binding remains incomplete. — IPv6 Source Guard with 'ipv6 verify source' uses the binding table to validate source addresses. Even with a static binding, the binding table entry must be in the 'REACHABLE' state for Source Guard to accept traffic. If the static binding is configured but the switch does not have a corresponding ND entry (because the host never sends an NS or the switch does not learn it), the binding remains in 'INCOMPLETE' state and Source Guard drops the traffic. The edge case is that static bindings do not automatically populate the ND cache; the host must send an unsolicited NA or the switch must receive an RS to complete the binding.
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.
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?
OSPF neighbours must agree on key parameters.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which configuration is missing to properly implement IPv6 First Hop Security on an access switch port that should only allow traffic from a single host with a static IPv6 address 2001:db8:1::10?
medium
✓ A.The interface needs 'ipv6 verify source' and a static binding entry 'ipv6 source binding 2001:db8:1::10 interface GigabitEthernet0/6'.
B.The interface needs 'ipv6 nd raguard' to block RAs.
C.The interface needs 'ipv6 dhcp guard' to block DHCP messages.
D.The interface needs 'ipv6 nd inspection' to validate ND messages.
Why A: To restrict traffic to a single host, you need IPv6 Source Guard with a static binding or a PACL. The missing piece is often the static binding or the source guard configuration.
Last reviewed: Jun 18, 2026
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