hardMultiple Choice
300-410 Practice Question: Runs the following command to debug IPv6 uRPF…
A network engineer runs the following command to debug IPv6 uRPF with detailed information:
R1# debug ipv6 verify detail
IPv6 verify debugging is on (detail)
*Mar 1 00:03:45.678: IPv6 verify: source 2001:DB8:5::1 on GigabitEthernet0/0 *Mar 1 00:03:45.678: route to source via GigabitEthernet0/1, not same as input interface
What does this output indicate?
⚠ Common exam trap
Cisco often tests the distinction between strict and loose uRPF modes, and the trap here is that candidates assume any valid route means the packet is forwarded, ignoring the critical interface match requirement for 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
✓
The packet will be dropped because strict uRPF requires the return path to be through the same interface.
The debug output shows that the source address 2001:DB8:5::1 is reachable via GigabitEthernet0/1, but the packet arrived on GigabitEthernet0/0. With strict unicast Reverse Path Forwarding (uRPF), the router verifies that the best return route to the source uses the same interface on which the packet was received. Since the interfaces do not match, the router drops the packet to prevent spoofing.
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 strict uRPF requires the return path to be through the same interface.
Why this is correct
Strict uRPF checks that the source address is reachable via the same interface the packet arrived on. Here the route to 2001:DB8:5::1 points to GigabitEthernet0/1, not the input GigabitEthernet0/0, so the packet fails the check and is dropped.
- ✗
The packet will be forwarded because a route exists.
Why it's wrong here
A route existing is insufficient under strict uRPF, which also requires the source route's egress interface to match the packet's ingress interface. Here they differ, so the packet is dropped; a route alone would suffice only under loose mode.
- ✗
The packet will be forwarded because uRPF is loose.
Why it's wrong here
Loose mode checks only that a route to the source exists, regardless of interface, so the mismatched input interface would not cause a drop. The output shows strict mode failing the interface match, meaning the packet is dropped; loose mode would be correct if configured.
- ✗
The router will change the route to use GigabitEthernet0/0.
Why it's wrong here
uRPF verification never rewrites the routing table; it only accepts or drops the packet based on the existing route. The output shows the source route pointing to GigabitEthernet0/1, so the router drops the packet rather than altering forwarding to GigabitEthernet0/0.
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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.