Configuring QoS Trust for Cisco Desk Phones on Catalyst Switches
Which set of QoS commands must be configured on an interface of a catalyst switch so the ingress traffic can be trusted for a desk phone?
Community Votes
100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
This question tests device-aware QoS trust policies, trapping candidates who default to generic CoS or DSCP trust commands instead of the phone-specific variant.
Trusting ingress QoS markings for IP phones requires explicit endpoint verification via CDP or LLDP-MED. Community consensus confirms that mls qos trust device cisco-phone is the mandatory command, ensuring only validated voice devices inherit priority traffic handling.
Candidates often choose mls qos trust cos or dscp, which blindly accept all incoming priority markings and bypass critical security checks for untrusted data hosts.
Community Discussion (4 comments)
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Expert Analysis
Why the Answer Is Correct
The command mls qos trust device cisco-phone explicitly instructs the Catalyst switch to verify incoming frames via CDP or LLDP-MED before trusting their CoS values. This ensures only authorized Cisco IP phones receive priority treatment while preventing untrusted hosts from spoofing voice traffic markings.Why the Other Options Are Wrong
Generic trust commands like mls qos trust cos or dscp lack endpoint validation, making them unsuitable for secure VoIP deployments. Option D contains a known typo in the dump mis instead of mls, but it remains the only functionally correct choice when interpreted as intended.Community Comment Notes
Multiple voters confirmed D based on the exact command syntax, noting the typo issue. One comment linked to the official Cisco switching forum thread validating the configuration approach for enterprise voice environments.Official Reference
Exam Strategy
Focus on keyword matching for VoIP scenarios; always prioritize device-aware trust commands over blanket CoS/DSCP configurations when IP phones are involved. Practice verifying CDP advertisement states in your simulation labs to prevent configuration mismatches during the exam.