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300-410 Practice Question: An engineer enables 'ipv6 destination guard' on a…
An engineer enables 'ipv6 destination guard' on a switch to prevent IPv6 address spoofing. After configuration, a legitimate host on a port is unable to receive traffic from the network, although it can send traffic. The host has a global unicast address. The switch logs show that destination guard is dropping packets destined to that host. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the interaction between IPv6 first-hop security features and privacy extensions, where candidates mistakenly think the issue is a trust configuration or address type rather than the dynamic nature of temporary addresses in the binding table.
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
✓
The host uses IPv6 privacy extensions and changes its address frequently, but the binding table only has the original address.
IPv6 destination guard relies on the IPv6 neighbor discovery (ND) binding table to validate destination addresses. If the host uses IPv6 privacy extensions (RFC 4941), it generates temporary addresses that change frequently. The binding table only contains the original address learned from the initial ND exchange, so packets destined to the new temporary address are dropped as spoofed, even though the traffic is legitimate.
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 host uses IPv6 privacy extensions and changes its address frequently, but the binding table only has the original address.
Why this is correct
Destination Guard relies on static bindings; privacy addresses are not learned.
- ✗
Destination Guard blocks all global unicast addresses by default.
Why it's wrong here
It only blocks addresses not in the binding table.
- ✗
The switch port is not configured as 'trusted' for destination guard.
Why it's wrong here
Destination Guard does not have a trust concept.
- ✗
The host is using a link-local address, which destination guard does not support.
Why it's wrong here
Destination Guard works with all unicast addresses.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco 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 300-410 exam.