Question 185 of 2,152

IPv6 First Hop Security →mediumMultiple ChoiceObjective-mapped

300-410 IPv6 First Hop Security Practice Question

This 300-410 practice question tests your understanding of ipv6 first hop security. 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 network engineer is troubleshooting an issue where IPv6 traffic from a host is being dropped by the switch. The switch has IPv6 Source Guard enabled. The host has a static IPv6 address 2001:db8:2::20. The engineer sees that the binding table does not contain an entry for this host. What should the engineer do to resolve the issue without disabling IPv6 Source Guard?

Question 1mediummultiple choice

Study the full IPv6 explanation →

A
Enable IPv6 ND snooping on the VLAN to allow the switch to learn the host's binding from Neighbor Discovery messages.
Correct because ND snooping creates bindings for static addresses, allowing IPv6 Source Guard to permit traffic.
B
Configure the host to use DHCPv6 to obtain an address so that the binding is learned via DHCPv6 snooping.
Why wrong: Incorrect because while DHCPv6 snooping would create a binding, the host is using a static address; changing the host configuration may not be desirable.
C
Add a static binding entry for the host in the IPv6 binding table using the 'ipv6 neighbor' command.
Why wrong: Incorrect because the 'ipv6 neighbor' command adds an entry to the switch's neighbor cache, not to the IPv6 Source Guard binding table; the binding table is populated by snooping.
D
Disable IPv6 Source Guard on the port connected to the host.
Why wrong: Incorrect because the question asks to resolve the issue without disabling IPv6 Source Guard.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Enable IPv6 ND snooping on the VLAN to allow the switch to learn the host's binding from Neighbor Discovery messages.

For static IPv6 addresses, IPv6 Source Guard relies on ND snooping to learn the binding. If ND snooping is not enabled, the binding will not be created, and traffic will be dropped. The fix is to enable ND snooping on the VLAN.

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.

✓
Enable IPv6 ND snooping on the VLAN to allow the switch to learn the host's binding from Neighbor Discovery messages.
Why this is correct
Correct because ND snooping creates bindings for static addresses, allowing IPv6 Source Guard to permit traffic.
Related concept
OSPF neighbours must agree on key parameters.
✗
Configure the host to use DHCPv6 to obtain an address so that the binding is learned via DHCPv6 snooping.
Why it's wrong here
Incorrect because while DHCPv6 snooping would create a binding, the host is using a static address; changing the host configuration may not be desirable.
✗
Add a static binding entry for the host in the IPv6 binding table using the 'ipv6 neighbor' command.
Why it's wrong here
Incorrect because the 'ipv6 neighbor' command adds an entry to the switch's neighbor cache, not to the IPv6 Source Guard binding table; the binding table is populated by snooping.
✗
Disable IPv6 Source Guard on the port connected to the host.
Why it's wrong here
Incorrect because the question asks to resolve the issue without disabling IPv6 Source Guard.

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.

Trap categories for this question

Command / output trap
Incorrect because the 'ipv6 neighbor' command adds an entry to the switch's neighbor cache, not to the IPv6 Source Guard binding table; the binding table is populated by snooping.

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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

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: Enable IPv6 ND snooping on the VLAN to allow the switch to learn the host's binding from Neighbor Discovery messages. — For static IPv6 addresses, IPv6 Source Guard relies on ND snooping to learn the binding. If ND snooping is not enabled, the binding will not be created, and traffic will be dropped. The fix is to enable ND snooping on the VLAN.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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