Refer to the exhibit. What is the effect when the switchport priority extend cos 3 command is
configured on the switch port interface connected to the IP phone?

A.
The IP phone is enabled to override with a CoS value of 3 the existing CoS marking of the
PC attached to the IP phone.

B.
The switch will no longer tag incoming voice packets and will extend the trust boundary to
the distribution layer switch.

C.
RTP will be used to negotiate a CoS value based upon bandwidth utilization on the link.

D.
Effectively, the trust boundary has been moved to the PC attached to the IP phone.

E.
The computer is now establishing the CoS value and has effectively become the trust
boundary.

Explanation:
The “switchport priority extend cos <priority>” is used to set the IP phone access port to
override the priority received from the PC or the attached device. The CoS value is a number
from 0 to 7. Seven is the highest priority. The default is 0. In this case, it has been set to
mark all traffic with a class of service value of 3.

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_14_ea1/c
onfiguration/guide/swvoip.html