- A
IPv6 source guard is dropping packets from sources not in the binding table, preventing spoofing.
The packet is dropped because the source address is not found in the binding table.
- B
IPv6 source guard is allowing the packet because the source MAC matches.
Why wrong: The packet is dropped, not allowed.
- C
IPv6 source guard is not configured; the debug output is from default IPv6 forwarding.
Why wrong: The debug references source guard, indicating it is configured.
- D
IPv6 source guard is learning the binding from the packet and will allow future packets.
Why wrong: The packet is dropped, and there is no indication of learning.
Question 1,192 of 2,152
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 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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
IPv6 source guard uses a binding table built by DHCPv6 snooping or IPv6 neighbor discovery (ND) snooping to validate source addresses on a per-port basis. When a packet arrives, the switch performs a lookup on the source IPv6 address and MAC; if no matching entry exists, the packet is dropped, preventing rogue devices from spoofing addresses. In real-world deployments, this is critical for mitigating attacks like IPv6 address spoofing in enterprise access layers, especially where DHCPv6 is used for address assignment.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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 |
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
IPv6 First Hop Security — study guide chapter
Learn the concepts, then practise the questions
- →
IPv6 First Hop Security practice questions
Targeted practice on this topic area only
- →
All 300-410 questions
2,152 questions across all exam domains
- →
Cisco CCNP ENARSI 300-410 study guide
Full concept coverage aligned to exam objectives
- →
300-410 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 300-410 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Layer 3 Technologies practice questions
Practise 300-410 questions linked to Layer 3 Technologies.
EIGRP Troubleshooting practice questions
Practise 300-410 questions linked to EIGRP Troubleshooting.
OSPF Troubleshooting (v2/v3) practice questions
Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).
BGP Troubleshooting practice questions
Practise 300-410 questions linked to BGP Troubleshooting.
Route Redistribution practice questions
Practise 300-410 questions linked to Route Redistribution.
Policy-Based Routing (PBR) practice questions
Practise 300-410 questions linked to Policy-Based Routing (PBR).
VRF-Lite practice questions
Practise 300-410 questions linked to VRF-Lite.
Route Maps and Route Filtering practice questions
Practise 300-410 questions linked to Route Maps and Route Filtering.
Administrative Distance practice questions
Practise 300-410 questions linked to Administrative Distance.
Route Summarization practice questions
Practise 300-410 questions linked to Route Summarization.
Bidirectional Forwarding Detection (BFD) practice questions
Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).
VPN Technologies practice questions
Practise 300-410 questions linked to VPN Technologies.
Practice this exam
Start a free 300-410 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this 300-410 question test?
IPv6 First Hop Security — This question tests IPv6 First Hop Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More 300-410 practice questions
- Drag and drop the steps to negotiate an IKEv2 IPsec site-to-site tunnel into the correct order, from first to last.
- Drag and drop the steps to troubleshoot an IPsec site-to-site VPN adjacency failure into the correct order, from first t…
- Drag and drop the steps to verify and validate the operational state of an IPsec site-to-site VPN into the correct order…
- Consider the following configuration snippet: ip cef ! interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.25…
- A router is configured with 'logging host 10.1.1.100' and 'logging trap informational'. The engineer notices that syslog…
- Drag and drop the steps to configure a GRE tunnel for IPv6 over IPv4 into the correct order, from first to last.
Last reviewed: Jul 4, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.