Question

A network engineer is deploying IP phones with attached PCs on access switches. The desk PCs are re-marking their own traffic with DSCP EF to gain priority, causing voice quality degradation for the phones during congestion. The engineer wants to enforce the QoS trust boundary at the correct location so that only the phone's markings are trusted while PC markings are reset. Where should the trust boundary be established and how?

Accepted Answer

Configure the access switch port to conditionally trust the Cisco IP phone via CDP, so the phone's markings are honored and the PC's markings are reclassified to a default/untrusted value at the phone's PC port

Answer

Configure the distribution switch uplink to trust DSCP so all downstream markings, including the PC's EF, are preserved end-to-end

Answer

Disable QoS on the access switch entirely so all traffic is treated equally and no re-marking conflicts occur

Answer

Configure the core switch to police all EF traffic to zero, dropping any packets marked EF regardless of source