Cisco Certified Network Associate (200-301 CCNA) – Question598


Refer to the exhibit. Which plan must be implemented to ensure optimal QoS marking practices on this network?

A. Trust the IP phone markings on SW1 and mark traffic entering SW2 at SW2
B. As traffic traverses MLS1 remark the traffic, but trust all markings at the access layer
C. Remark traffic as it traverses R1 and trust all markings at the access layer.
D. As traffic enters from the access layer on SW1 and SW2, trust all traffic markings.

Correct Answer: A

Explanation:

Explanation:
Tell the switch to trust CoS markings from a Cisco IP phone on the access port. Cisco IP phones use 802.1q tags, these .1q tags contain the CoS value, to mark voice traffic at layer 2. When it’s forwarded upstream, the DSCP value is trusted (on the uplink port) and unchanged, but the .1q tag (and with it the CoS value) is stripped off by the upstream switch when received over the trunk.