Question 170 of 2,152

NetFlow and Flexible NetFlow →hardMultiple ChoiceObjective-mapped

300-410 NetFlow and Flexible NetFlow Practice Question

This 300-410 practice question tests your understanding of netflow and flexible netflow. 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. After the configuration, legitimate traffic from a customer network is being dropped. The engineer verifies that the customer's IP prefix is in the routing table. 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.

A
The router has multiple equal-cost paths to the customer network, and the return path uses a different interface, causing strict uRPF to drop the packet.
Strict uRPF requires that the best route to the source points back to the receiving interface. If there are multiple equal-cost paths, the router may choose a different interface for the return path, causing drops.
B
The customer network uses private IP addresses that are not routable, so uRPF drops them.
Why wrong: uRPF does not care about private vs public IPs; it only checks the routing table.
C
The interface is configured with 'ip verify unicast source reachable-via any', which is loose mode, not strict mode.
Why wrong: The scenario says strict mode is configured, so this is not the issue.
D
The routing table has a default route that points to a different interface, causing uRPF to use the default route for verification.
Why wrong: By default, uRPF does not use default routes for verification unless the 'allow-default' option is configured. If a default route exists, it may cause issues, but the scenario says the customer prefix is in the routing table, so the default route is not used.

Full breakdown with real-world context →

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 router has multiple equal-cost paths to the customer network, and the return path uses a different interface, causing strict uRPF to drop the packet.

Strict uRPF checks that the source IP of incoming packets has a route back to the same interface. If there is asymmetric routing, where the return path goes out a different interface, strict uRPF will drop the packets. A common edge case is when the router has multiple equal-cost paths to the source network, and the return traffic uses a different interface than the one the packet arrived on. In such cases, uRPF strict mode will fail because it only checks the best route, not all routes.

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 router has multiple equal-cost paths to the customer network, and the return path uses a different interface, causing strict uRPF to drop the packet.
Why this is correct
Strict uRPF requires that the best route to the source points back to the receiving interface. If there are multiple equal-cost paths, the router may choose a different interface for the return path, causing 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 customer network uses private IP addresses that are not routable, so uRPF drops them.
Why it's wrong here
uRPF does not care about private vs public IPs; it only checks the routing table.
✗
The interface is configured with 'ip verify unicast source reachable-via any', which is loose mode, not strict mode.
Why it's wrong here
The scenario says strict mode is configured, so this is not the issue.
✗
The routing table has a default route that points to a different interface, causing uRPF to use the default route for verification.
Why it's wrong here
By default, uRPF does not use default routes for verification unless the 'allow-default' option is configured. If a default route exists, it may cause issues, but the scenario says the customer prefix is in the routing table, so the default route is not used.

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.

Trap categories for this question

Scenario analysis trap
The scenario says strict mode is configured, so this is not the issue.

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

NetFlow and Flexible NetFlow — This question tests NetFlow and Flexible NetFlow — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The router has multiple equal-cost paths to the customer network, and the return path uses a different interface, causing strict uRPF to drop the packet. — Strict uRPF checks that the source IP of incoming packets has a route back to the same interface. If there is asymmetric routing, where the return path goes out a different interface, strict uRPF will drop the packets. A common edge case is when the router has multiple equal-cost paths to the source network, and the return traffic uses a different interface than the one the packet arrived on. In such cases, uRPF strict mode will fail because it only checks the best route, not all routes.

What should I do if I get this 300-410 question wrong?

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.

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