- A
The 'ip verify unicast source reachable-via any' command was used instead of 'rx'.
Why wrong: That would be loose mode, which would not drop the traffic.
- B
The router has a default route pointing out the same interface, causing uRPF to pass all traffic.
Why wrong: Default route can cause uRPF to pass traffic that should be dropped.
- C
The customer traffic is arriving on an interface where the return path to the source is via a different interface, violating strict uRPF.
Strict uRPF requires symmetric routing; asymmetric routing causes drops.
- D
The 'ip urpf allow-default' command is missing, causing default routes to be ignored.
Why wrong: Allow-default affects loose mode, not strict mode.
Question 991 of 2,152
Why Strict uRPF Drops Legitimate Traffic: Asymmetric Routing Explained
This 300-410 practice question tests your understanding of route redistribution. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 configures unicast Reverse Path Forwarding (uRPF) in strict mode on an interface facing the Internet. Legitimate traffic from a customer network is being dropped. The traffic has a source IP that belongs to the customer's prefix, which is reachable via a different interface on the router. 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 strict uRPF drops legitimate traffic when asymmetric routing forces the return path to the source IP out a different interface than the one where the packet arrived. Strict mode performs a two-part check: it verifies that the source address exists in the routing table and, critically, that the best reverse path to that source exits through the exact interface where the packet was received. When traffic from a customer network enters via one interface but the router’s best route back to that source points out a different interface—a classic asymmetric routing scenario—the strict check fails, and the packet is silently dropped. On the Cisco CCNP ENARSI 300-410 exam, this is a favorite trap: candidates often assume uRPF only checks for a route, forgetting the interface-matching requirement. The key memory tip is “Strict means same interface in and out; if the path splits, the packet splits.”
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 customer traffic is arriving on an interface where the return path to the source is via a different interface, violating strict uRPF.
Strict uRPF checks that the source IP of incoming packets has a route back out the same interface. If the best path to the source IP is via a different interface (asymmetric routing), the packet is dropped. This is a classic edge case with strict uRPF in asymmetric routing scenarios.
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.
- ✗
The 'ip verify unicast source reachable-via any' command was used instead of 'rx'.
Why it's wrong here
That would be loose mode, which would not drop the traffic.
- ✗
The router has a default route pointing out the same interface, causing uRPF to pass all traffic.
Why it's wrong here
Default route can cause uRPF to pass traffic that should be dropped.
- ✓
The customer traffic is arriving on an interface where the return path to the source is via a different interface, violating strict uRPF.
Why this is correct
Strict uRPF requires symmetric routing; asymmetric routing causes drops.
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 'ip urpf allow-default' command is missing, causing default routes to be ignored.
Why it's wrong here
Allow-default affects loose mode, not strict mode.
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.
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.
- →
Route Redistribution — study guide chapter
Learn the concepts, then practise the questions
- →
Route Redistribution practice questions
Targeted practice on this topic area only
- →
All 300-410 questions
2,152 questions across all exam domains
- →
Cisco CCNP ENARSI 300-410 study guide
Full concept coverage aligned to exam objectives
- →
300-410 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 300-410 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Layer 3 Technologies practice questions
Practise 300-410 questions linked to Layer 3 Technologies.
EIGRP Troubleshooting practice questions
Practise 300-410 questions linked to EIGRP Troubleshooting.
OSPF Troubleshooting (v2/v3) practice questions
Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).
BGP Troubleshooting practice questions
Practise 300-410 questions linked to BGP Troubleshooting.
Route Redistribution practice questions
Practise 300-410 questions linked to Route Redistribution.
Policy-Based Routing (PBR) practice questions
Practise 300-410 questions linked to Policy-Based Routing (PBR).
VRF-Lite practice questions
Practise 300-410 questions linked to VRF-Lite.
Route Maps and Route Filtering practice questions
Practise 300-410 questions linked to Route Maps and Route Filtering.
Administrative Distance practice questions
Practise 300-410 questions linked to Administrative Distance.
Route Summarization practice questions
Practise 300-410 questions linked to Route Summarization.
Bidirectional Forwarding Detection (BFD) practice questions
Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).
VPN Technologies practice questions
Practise 300-410 questions linked to VPN Technologies.
Practice this exam
Start a free 300-410 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this 300-410 question test?
Route Redistribution — This question tests Route Redistribution — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The customer traffic is arriving on an interface where the return path to the source is via a different interface, violating strict uRPF. — Strict uRPF checks that the source IP of incoming packets has a route back out the same interface. If the best path to the source IP is via a different interface (asymmetric routing), the packet is dropped. This is a classic edge case with strict uRPF in asymmetric routing scenarios.
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
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More 300-410 practice questions
- Drag and drop the steps to negotiate an IKEv2 IPsec site-to-site tunnel into the correct order, from first to last.
- Drag and drop the steps to troubleshoot an IPsec site-to-site VPN adjacency failure into the correct order, from first t…
- Drag and drop the steps to verify and validate the operational state of an IPsec site-to-site VPN into the correct order…
- Consider the following configuration snippet: ip cef ! interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.25…
- A router is configured with 'logging host 10.1.1.100' and 'logging trap informational'. The engineer notices that syslog…
- Drag and drop the steps to configure a GRE tunnel for IPv6 over IPv4 into the correct order, from first to last.
Last reviewed: Jun 18, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.