350-601 Compute Practice Question
Exhibit
Refer to the exhibit.
<config>
<system>
<qos>
<class-map name="BulkData">
<match qos-group="5"/>
</class-map>
<policy-map name="DataCenter">
<class name="BulkData">
<set qos-group="5"/>
<bandwidth percent="30"/>
</class>
<class class-default>
<bandwidth percent="70"/>
</class>
</policy-map>
</qos>
</system>
</config>Refer to the exhibit. An engineer applies this QoS policy to a Cisco Nexus 9000 switch in a data center. After applying the policy, storage traffic (iSCSI) is experiencing high latency and occasional drops. The engineer verifies that the iSCSI traffic is not matching the 'BulkData' class. What is the most likely cause of the issue?
⚠ Common exam trap
Cisco often tests the misconception that simply classifying traffic into a class-map is sufficient, but the trap here is that without a priority queue, latency-sensitive traffic like iSCSI will still suffer from high latency and drops even if correctly classified.
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 policy-map does not specify a priority queue for latency-sensitive traffic.
ISCSI is a latency-sensitive storage protocol that requires a strict priority queue to ensure low latency and minimal jitter. Without a priority queue configured in the policy-map, iSCSI traffic competes with other traffic classes on a best-effort basis, leading to high latency and drops even if it is not matching the 'BulkData' class.
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 policy-map does not specify a priority queue for latency-sensitive traffic.
Why this is correct
iSCSI requires low latency; without a priority queue, it competes with other traffic.
- ✗
The policy-map is applied at the system level, but iSCSI traffic is not classified under any class-map.
Why it's wrong here
iSCSI falls into class-default, but that doesn't cause drops; the lack of priority does.
- ✗
The bandwidth percent for class-default is too low, causing iSCSI to be starved.
Why it's wrong here
While 70% may be sufficient, the primary issue is lack of priority, not bandwidth starvation.
- ✗
The class-map 'BulkData' does not match the correct traffic because the match statement uses qos-group instead of dscp.
Why it's wrong here
Matching on qos-group is valid; the issue is not about matching.
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