Question 160 of 2,015

NetFlow and Telemetry →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to define a flow record that matches the specific application using NBAR or an ACL, and apply a flow monitor with a sampler rate to reduce CPU impact. This approach is the most efficient because Flexible NetFlow allows you to filter traffic at the flow record level, isolating only the suspect application, while the sampler reduces the number of packets inspected per second, thereby offloading the switch’s CPU from processing every single flow. On the ENCOR 350-401 exam, this scenario tests your understanding of how to balance granular application visibility with hardware performance—a common trap is assuming that capturing all flows or using SPAN mirrors is acceptable, but both would spike CPU utilization on a Catalyst 9300. Remember the key principle: filter first, then sample. A useful memory tip is “Match and Sample” — match the application with NBAR or an ACL, then apply a sampler to keep the CPU cool.

350-401 NetFlow and Telemetry Practice Question

This 350-401 practice question tests your understanding of netflow and telemetry. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 network engineer is troubleshooting a performance issue on a Cisco Catalyst 9300 switch. The engineer suspects that a specific application is using excessive bandwidth. The switch supports Flexible NetFlow. The engineer wants to monitor only the traffic from that application without affecting the switch's CPU. What is the most efficient way to configure this?

Question 1hardmultiple choice

Read the full network assurance explanation →

A
Define a flow record that matches the specific application using NBAR or an ACL, and apply a flow monitor with a sampler rate to reduce CPU impact.
Correct because matching only the application of interest and using a sampler minimizes the number of flows processed, reducing CPU load.
B
Enable NetFlow on all interfaces and export all flows to the collector, then filter at the collector.
Why wrong: Incorrect because capturing all flows increases CPU usage on the switch, which may exacerbate performance issues.
C
Use SNMP to poll interface counters and calculate the bandwidth used by the application.
Why wrong: Incorrect because SNMP provides aggregate interface counters, not per-application granularity.
D
Configure port mirroring (SPAN) to send all traffic to an external probe for analysis.
Why wrong: Incorrect because port mirroring sends all traffic, increasing CPU load on the switch and potentially worsening performance.

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 flow record that matches the specific application using NBAR or an ACL, and apply a flow monitor with a sampler rate to reduce CPU impact.

Flexible NetFlow allows filtering to reduce CPU impact. Option A is correct because using a flow record with a match on the application (e.g., NBAR or ACL) and a sampler reduces the number of flows processed. Option B is incorrect because capturing all flows would increase CPU load. Option C is incorrect because SNMP polling gives aggregate data, not per-application. Option D is incorrect because mirroring all traffic to a probe would also increase CPU load.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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 flow record that matches the specific application using NBAR or an ACL, and apply a flow monitor with a sampler rate to reduce CPU impact.
Why this is correct
Correct because matching only the application of interest and using a sampler minimizes the number of flows processed, reducing CPU load.
Related concept
Standard ACLs match source addresses.
✗
Enable NetFlow on all interfaces and export all flows to the collector, then filter at the collector.
Why it's wrong here
Incorrect because capturing all flows increases CPU usage on the switch, which may exacerbate performance issues.
✗
Use SNMP to poll interface counters and calculate the bandwidth used by the application.
Why it's wrong here
Incorrect because SNMP provides aggregate interface counters, not per-application granularity.
✗
Configure port mirroring (SPAN) to send all traffic to an external probe for analysis.
Why it's wrong here
Incorrect because port mirroring sends all traffic, increasing CPU load on the switch and potentially worsening performance.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 350-401 ACL questions on filtering logic and placement.

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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 — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: Define a flow record that matches the specific application using NBAR or an ACL, and apply a flow monitor with a sampler rate to reduce CPU impact. — Flexible NetFlow allows filtering to reduce CPU impact. Option A is correct because using a flow record with a match on the application (e.g., NBAR or ACL) and a sampler reduces the number of flows processed. Option B is incorrect because capturing all flows would increase CPU load. Option C is incorrect because SNMP polling gives aggregate data, not per-application. Option D is incorrect because mirroring all traffic to a probe would also increase CPU load.

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

What is the key concept behind this question?

Standard ACLs match source addresses.

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