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Collaboration, Voice & AV · Intermediate

Conditional Trust

A switch QoS setting that trusts endpoint markings only when a specific device, such as a Cisco IP phone, is detected via CDP.

Definition

With conditional trust, the access port trusts DSCP or CoS from an attached Cisco phone and remarks traffic to zero if no phone is detected, preventing PCs from marking their own traffic as EF. The phone itself can re-mark traffic from the attached PC. This extends the QoS trust boundary to the phone.

Example

trust device cisco-phone on a Catalyst access port trusts markings only when CDP sees a Cisco phone.

Exam tip

Conditional trust relies on CDP; third-party phones may require LLDP-based or ACL-based classification.

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