Courseiva
← 300-410
Full test
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:

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

    The debug line "no route to source" means the FIB lookup for 2001:DB8:4::1 failed, so strict uRPF cannot validate the return path and discards the packet. This satisfies the stem's requirement of identifying the drop cause directly from the verify output.

  • ✗

    The packet will be forwarded because uRPF only checks the destination.

    Why it's wrong here

    uRPF verifies the source address against the routing table, not the destination, so this reasoning is inverted. The "no route to source" message confirms the source check failed, causing a drop. Destination-based forwarding checks occur separately, after any uRPF pass.

  • ✗

    The packet will be forwarded because the source is on the same interface.

    Why it's wrong here

    The debug line "no route to source" means the router lacks a route back to 2001:DB8:4::1, so strict uRPF drops the packet rather than forwarding it. Same-interface source reachability is irrelevant here; the failure is the missing reverse-path route, not interface locality.

  • ✗

    The router will add a route to the source address.

    Why it's wrong here

    Debug output reports a verification result; it never installs a route. The router has no route to the source, so uRPF drops the packet instead of adding a forwarding entry. Route installation comes from routing protocols or static configuration, not from uRPF verification.

About these practice questions

One of 1,401 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 →

How Courseiva writes practice questions · Editorial policy

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.