Question 1,141 of 2,015

NetFlow and Telemetry →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct approach is to define a custom flow record that includes the 'match ipv4 vlan' or 'match ipv4 vrf' field to identify each customer's traffic, and apply a single flow monitor on the shared interface. This works because Flexible NetFlow allows you to customize flow records with key fields like VRF or VLAN, which act as unique tags to separate flows per customer even when multiple customers share the same physical interface. On the ENCOR 350-401 exam, this question tests your understanding of Flexible NetFlow’s ability to export per-customer data without needing separate monitors or export destinations—a common trap is assuming you must create multiple flow monitors per interface, which would still mix flows if customers share a link. Remember, the key is to match on the VRF or VLAN field within a single flow record, not to multiply monitors. Memory tip: “One monitor, match the VRF—keep customers separate without grief.”

CCNP NetFlow and Telemetry Practice Question

This 350-401 practice question tests your understanding of netflow and telemetry. 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.

A service provider is using Cisco ASR 9000 routers and needs to collect NetFlow data from multiple customers' traffic. The engineer wants to ensure that flow records from different customers are not mixed and can be identified separately. The router supports Flexible NetFlow. What is the best approach?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

Question 1hardmultiple choice

Read the full network assurance explanation →

A
Define a custom flow record that includes the 'match ipv4 vlan' or 'match ipv4 vrf' field to identify each customer's traffic, and apply a single flow monitor on the shared interface.
Correct because including the VRF or VLAN match field in the flow record allows the collector to distinguish flows per customer.
B
Configure a separate flow monitor for each customer interface and export to different collectors.
Why wrong: Incorrect because if customers share an interface (e.g., MPLS VPN), separate monitors won't separate flows; also, multiple collectors add complexity.
C
Use NetFlow v9 export with the 'match ipv4 source address' field only, and rely on the collector to separate by source IP.
Why wrong: Incorrect because source IP alone may not uniquely identify customers if they use overlapping private IPs.
D
Enable SNMP interface polling to track per-customer traffic statistics.
Why wrong: Incorrect because SNMP provides aggregate interface counters, not per-flow or per-customer granularity.

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

✓

Define a custom flow record that includes the 'match ipv4 vlan' or 'match ipv4 vrf' field to identify each customer's traffic, and apply a single flow monitor on the shared interface.

Flexible NetFlow allows customization of flow records. Option A is correct by using a flow record with a 'match ipv4 vlan' or 'match ipv4 vrf' field to tag flows per customer. Option B is incorrect because separate flow monitors for each interface would still mix flows if multiple customers share an interface. Option C is incorrect because NetFlow v9 export format does not inherently separate customers. Option D is incorrect because SNMP is not suitable for per-customer flow identification.

Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
Define a custom flow record that includes the 'match ipv4 vlan' or 'match ipv4 vrf' field to identify each customer's traffic, and apply a single flow monitor on the shared interface.
Why this is correct
Correct because including the VRF or VLAN match field in the flow record allows the collector to distinguish flows per customer.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
Configure a separate flow monitor for each customer interface and export to different collectors.
Why it's wrong here
Incorrect because if customers share an interface (e.g., MPLS VPN), separate monitors won't separate flows; also, multiple collectors add complexity.
✗
Use NetFlow v9 export with the 'match ipv4 source address' field only, and rely on the collector to separate by source IP.
Why it's wrong here
Incorrect because source IP alone may not uniquely identify customers if they use overlapping private IPs.
✗
Enable SNMP interface polling to track per-customer traffic statistics.
Why it's wrong here
Incorrect because SNMP provides aggregate interface counters, not per-flow or per-customer granularity.

Common exam traps

Common exam trap: an active trunk can still block the VLAN you need

A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.

Detailed technical explanation

How to think about this question

VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.

KKey Concepts to Remember

Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.

TExam Day Tips

Use show vlan brief to verify access VLANs.
Use show interfaces trunk to verify trunk state and allowed VLANs.
Do not treat every same-VLAN issue as a routing problem.

Key takeaway

A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

Real-world example

How this comes up in practice

A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.

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FAQ

Questions learners often ask

What does this 350-401 question test?

NetFlow and Telemetry — This question tests NetFlow and Telemetry — Access ports place end devices into a single VLAN..

What is the correct answer to this question?

The correct answer is: Define a custom flow record that includes the 'match ipv4 vlan' or 'match ipv4 vrf' field to identify each customer's traffic, and apply a single flow monitor on the shared interface. — Flexible NetFlow allows customization of flow records. Option A is correct by using a flow record with a 'match ipv4 vlan' or 'match ipv4 vrf' field to tag flows per customer. Option B is incorrect because separate flow monitors for each interface would still mix flows if multiple customers share an interface. Option C is incorrect because NetFlow v9 export format does not inherently separate customers. Option D is incorrect because SNMP is not suitable for per-customer flow identification.

What should I do if I get this 350-401 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Access ports place end devices into a single VLAN.

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