- A
uRPF strict mode requires the reverse path to be via the same interface; asymmetric routing causes drops.
Strict mode fails if the return route uses a different interface, which is common in DMVPN.
- B
The hub's IP address is not in the routing table, so uRPF drops the packet.
Why wrong: The hub is reachable, but via a different path.
- C
uRPF must be configured with the `allow-default` option to accept packets with default route.
Why wrong: Allow-default helps if the default route is used, but the issue is asymmetric routing.
- D
uRPF is not supported on tunnel interfaces; it must be applied on the physical interface.
Why wrong: uRPF is supported on tunnel interfaces.
Question 1,672 of 2,152
uRPF Strict Mode in DMVPN
This 300-410 practice question tests your understanding of eigrp troubleshooting. 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.
An engineer enables uRPF (unicast Reverse Path Forwarding) in strict mode on an interface connected to a DMVPN spoke. The spoke has multiple tunnels and receives traffic from the hub with a source IP that is not the best reverse path. Unexpectedly, the spoke drops all traffic from the hub, even though the hub is reachable via the tunnel. Which is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Quick Answer
The answer is that uRPF strict mode drops traffic from the hub because it requires the reverse path to the source to exit via the same interface the packet arrived on, and in a DMVPN spoke with multiple tunnels, asymmetric routing often violates this check. When the spoke receives a packet from the hub on its tunnel interface, uRPF strict mode performs a route lookup for the hub’s source IP; if the best reverse path points out a different interface—such as the physical WAN interface—the packet is discarded, even though the hub is reachable. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how uRPF interacts with DMVPN’s dynamic overlay topology, where the hub’s source address may be learned via a separate routing process. A common trap is assuming reachability alone satisfies uRPF, but strict mode demands interface symmetry. Remember: strict equals same interface, loose equals any interface—if your DMVPN drops, check the reverse path’s exit.
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
✓
uRPF strict mode requires the reverse path to be via the same interface; asymmetric routing causes drops.
uRPF strict mode checks that the source IP of incoming packets has a route back to the source via the same interface. In DMVPN, the hub's source IP may be reachable via a different interface (e.g., physical interface) than the tunnel interface where the packet arrives. This asymmetric routing causes uRPF strict mode to drop the packets. The solution is to use loose mode or allow-default.
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.
- ✓
uRPF strict mode requires the reverse path to be via the same interface; asymmetric routing causes drops.
Why this is correct
Strict mode fails if the return route uses a different interface, which is common in DMVPN.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The hub's IP address is not in the routing table, so uRPF drops the packet.
Why it's wrong here
The hub is reachable, but via a different path.
- ✗
uRPF must be configured with the `allow-default` option to accept packets with default route.
Why it's wrong here
Allow-default helps if the default route is used, but the issue is asymmetric routing.
- ✗
uRPF is not supported on tunnel interfaces; it must be applied on the physical interface.
Why it's wrong here
uRPF is supported on tunnel interfaces.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: uRPF strict mode requires the reverse path to be via the same interface; asymmetric routing causes drops. — uRPF strict mode checks that the source IP of incoming packets has a route back to the source via the same interface. In DMVPN, the hub's source IP may be reachable via a different interface (e.g., physical interface) than the tunnel interface where the packet arrives. This asymmetric routing causes uRPF strict mode to drop the packets. The solution is to use loose mode or allow-default.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 18, 2026
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