Question

A network engineer is deploying QoS on the access layer of a campus network. IP phones connect to access switches, and PCs connect through the phones. The engineer wants to ensure that voice traffic is prioritized while preventing users from manipulating DSCP markings on their PCs to gain unfair bandwidth. Where should the trust boundary be established, and how should PC traffic be handled?

Accepted Answer

Establish the trust boundary at the IP phone; trust CoS from the phone but have the switch re-mark or untrust DSCP from the attached PC

Answer

Trust markings at the access switch uplink to the distribution layer, and trust all traffic arriving on access ports

Answer

Establish the trust boundary at the distribution layer switch and configure the access switch to trust nothing

Answer

Trust DSCP markings from the PC directly, since endpoints are the most accurate source of application marking