mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Runs the following command to troubleshoot IPv6…
A network engineer runs the following command to troubleshoot IPv6 source guard:
R1# debug ipv6 source-guard *Mar 1 00:04:56.789: IPv6-Source-Guard: R1, Fa0/0, IPv6 packet from 2001:db8::5, src MAC 0011.2233.4455, dst 2001:db8::1 *Mar 1 00:04:56.789: IPv6-Source-Guard: R1, Fa0/0, Binding lookup: 2001:db8::5 not found in binding table *Mar 1 00:04:56.789: IPv6-Source-Guard: R1, Fa0/0, Packet dropped: source 2001:db8::5 not allowed
What does this output indicate?
⚠ Common exam trap
Cisco often tests the misconception that IPv6 source guard can dynamically learn bindings from any traffic, when in fact it requires a pre-built binding table from DHCPv6 snooping or ND snooping to function correctly.
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
✓
IPv6 source guard is dropping packets from sources not in the binding table, preventing spoofing.
The debug output shows that IPv6 source guard is actively dropping a packet from source address 2001:db8::5 because that address is not found in the binding table. This is the core function of IPv6 source guard: it filters traffic based on the source IPv6 address and MAC address, using the binding table (populated by DHCPv6 snooping or ND snooping) to prevent spoofing attacks. The packet is dropped because the source address is not allowed, confirming that option A is correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
IPv6 source guard is dropping packets from sources not in the binding table, preventing spoofing.
Why this is correct
The packet is dropped because the source address is not found in the binding table.
- ✗
IPv6 source guard is allowing the packet because the source MAC matches.
Why it's wrong here
The packet is dropped, not allowed.
- ✗
IPv6 source guard is not configured; the debug output is from default IPv6 forwarding.
Why it's wrong here
The debug references source guard, indicating it is configured.
- ✗
IPv6 source guard is learning the binding from the packet and will allow future packets.
Why it's wrong here
The packet is dropped, and there is no indication of learning.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
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JA
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.