hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Runs the following command to debug IPv6 uRPF:…
A network engineer runs the following command to debug IPv6 uRPF:
R1# debug ipv6 verify
IPv6 verify debugging is on
*Mar 1 00:02:34.567: IPv6 verify: source 2001:DB8:4::1 on GigabitEthernet0/0 *Mar 1 00:02:34.567: no route to source
What does this output indicate?
⚠ Common exam trap
Cisco often tests the misconception that uRPF checks the destination address or that it only verifies the source is on the same interface without requiring a route, but the key trap here is that 'no route to source' means the packet is dropped, not forwarded, because uRPF cannot validate the source without a matching route in the routing 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 packet will be dropped because uRPF cannot find a route to the source address.
The debug output shows that uRPF (unicast Reverse Path Forwarding) checked the source address 2001:DB8:4::1 on the incoming interface GigabitEthernet0/0 and found no route to that source in the IPv6 routing table. When uRPF is enabled and a packet arrives on an interface, the router performs a reverse path lookup: it checks whether the best return route to the source address points back to the same interface. If no route exists at all, the lookup fails, and uRPF considers the source as unreachable, causing the packet to be dropped. This is a strict-mode uRPF behavior, and the debug message 'no route to source' confirms the packet will be discarded.
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 packet will be dropped because uRPF cannot find a route to the source address.
Why this is correct
Correct. uRPF requires a route to the source; if none exists, the packet is dropped.
- ✗
The packet will be forwarded because uRPF only checks the destination.
Why it's wrong here
Incorrect. uRPF checks the source address.
- ✗
The packet will be forwarded because the source is on the same interface.
Why it's wrong here
Incorrect. Even if on the same interface, a route is required.
- ✗
The router will add a route to the source address.
Why it's wrong here
Incorrect. uRPF does not add routes; it only verifies.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
uRPF
Unicast Reverse Path Forwarding is a network security feature that verifies the source address of incoming packets to prevent IP spoofing attacks.
Key term
IPv6 Next Hop Resolution
IPv6 Next Hop Resolution is the process a router uses to determine the next router or destination device to which a packet should be forwarded, based on the destination IPv6 address and the routing table.
About these practice questions
One of 1,966 original 300-410 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
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.