- A
It verifies that the source address is in the routing table, but does not check the incoming interface.
Why wrong: That describes loose mode, not strict mode.
- B
It checks that the source address is reachable via the same interface and that the route is a connected route.
Why wrong: The route does not have to be connected; it must point back to the same interface.
- C
It verifies that the source address is reachable via the same interface and that the route points back to that interface.
This is the definition of strict mode uRPF.
- D
It only checks that the source address is not a multicast or link-local address.
Why wrong: uRPF does not filter based on address type; it checks reachability.
Question 1,558 of 2,152
300-410 IPv6 Traffic Filtering and uRPF Practice Question
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which statement correctly describes the behavior of IPv6 Unicast Reverse Path Forwarding (uRPF) in strict mode?
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
✓
It verifies that the source address is reachable via the same interface and that the route points back to that interface.
IPv6 uRPF strict mode requires that the source address of an incoming packet is reachable via the exact same interface on which the packet arrived, and that the best matching route in the FIB points back to that interface. This prevents spoofed traffic by ensuring the source is topologically correct from the router's perspective, as defined in RFC 3704.
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.
- ✗
It verifies that the source address is in the routing table, but does not check the incoming interface.
Why it's wrong here
That describes loose mode, not strict mode.
- ✗
It checks that the source address is reachable via the same interface and that the route is a connected route.
Why it's wrong here
The route does not have to be connected; it must point back to the same interface.
- ✓
It verifies that the source address is reachable via the same interface and that the route points back to that interface.
Why this is correct
This is the definition of strict mode uRPF.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
It only checks that the source address is not a multicast or link-local address.
Why it's wrong here
uRPF does not filter based on address type; it checks reachability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between strict and loose mode, and the trap here is that candidates confuse 'route points back to that interface' with 'route is a connected route,' leading them to incorrectly select Option B.
Detailed technical explanation
How to think about this question
Under the hood, uRPF strict mode performs a FIB lookup on the source IPv6 address and verifies that the outgoing interface in the FIB entry matches the ingress interface of the packet. This behavior is critical in asymmetric routing scenarios where strict mode can drop legitimate traffic if paths are not symmetric, which is why loose mode exists as an alternative. In real-world deployments, strict mode is often used on customer-facing interfaces to prevent source address spoofing in a controlled topology.
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.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: It verifies that the source address is reachable via the same interface and that the route points back to that interface. — IPv6 uRPF strict mode requires that the source address of an incoming packet is reachable via the exact same interface on which the packet arrived, and that the best matching route in the FIB points back to that interface. This prevents spoofed traffic by ensuring the source is topologically correct from the router's perspective, as defined in RFC 3704.
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.
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Last reviewed: Jul 4, 2026
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