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Question :-

What is one of the reasons that custom QoS ACLs are recommended over automatic QoS when configuring ports on a Catalyst 6500 for use with IP phones?
79xx IP phones do not automatically mark voice packets with non-zero DSCP values.
79xx IP phones do not mark protocol packets such as DHCP, DNS, or TFTP with non-zero DSCP values.
79xx IP phones do not mark voice packets with optimal DSCP values.
79xx IP phones use a custom protocol to communicate CDP information to the switch.

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