mediumMultiple Choice
CCNP Practice Question: Runs the following command on Router R3: R3# show…
A network engineer runs the following command on Router R3:
R3# show mls qos interface GigabitEthernet0/1
GigabitEthernet0/1 trust state: trust DSCP trust mode: trust dscp COS override: dis default COS: 0 DSCP Mutation Map: default dscp mutation map trust device: none qos mode: port-based
R3# show mls qos
QoS is enabled globally QoS global counters: total packets not matching QoS criteria = 0 Total packets with known CoS = 0 Total packets dropped by policing = 0
Based on this output, what can be concluded?
⚠ Common exam trap
Cisco often tests the distinction between 'trust DSCP' and 'trust CoS'—the trap here is that candidates may confuse the 'trust state: trust DSCP' output with trusting CoS, especially when the 'default COS' field is present, leading them to incorrectly select Option A or B.
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 interface trusts the DSCP markings of incoming packets.
The output shows 'trust state: trust DSCP' and 'trust mode: trust dscp', which explicitly indicates that the interface trusts the DSCP markings of incoming packets. Additionally, 'qos mode: port-based' confirms that QoS is enabled on the interface, and the global QoS status shows 'QoS is enabled globally'. Therefore, the interface will preserve and use the incoming DSCP values for QoS classification.
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 interface is configured to trust CoS values.
Why it's wrong here
The show output explicitly reveals the trust mode as 'trust dscp' and 'trust state: trust DSCP', not CoS. CoS is an 802.1p priority field carried in the VLAN tag on trunk links, whereas DSCP is a Layer 3 IP header field. If the interface were configured to trust CoS, the output would show 'trust cos' or 'trust state: trust CoS' instead.
- ✗
The interface will overwrite incoming DSCP values with default CoS.
Why it's wrong here
Trust DSCP is a passive classification mode: the interface reads the existing DSCP marking and uses it to determine the internal packet queue, but it does not modify the DSCP field. Overwriting incoming DSCP with a default CoS would require rewriting the packet with an untrusted (or 'ignore') policy, which is not what the output indicates. Moreover, DSCP and CoS are different fields at different layers, so a 'default CoS' cannot overwrite DSCP without explicitly re-marking the packet.
- ✓
The interface trusts the DSCP markings of incoming packets.
Why this is correct
The command output states 'trust state: trust DSCP' and 'trust mode: trust dscp', confirming that the interface is configured to honor the DSCP markings carried in the IP header of incoming packets. In this mode, the switch classifies each packet according to its DSCP value and maps that value to the appropriate QoS queue or policy, without altering the original DSCP field.
- ✗
QoS is disabled globally.
Why it's wrong here
The output includes the line 'QoS is enabled globally', so QoS is definitely not disabled at the global level. What is configured here is a per-interface trust behavior; global QoS enablement is a prerequisite for applying trust policies on an interface, and this output proves that prerequisite is met.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 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 350-401 exam.