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Software Configuration Guide—Release 12.2(25)SG
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Chapter 27 Configuring Quality of Service
Overview of QoS
• Perform the classification based on a configured IP standard or extended ACL, which examines
various fields in the IP header. If no ACL is configured, the packet is assigned the default DSCP
based on the trust state of the ingress port; otherwise, the policy map specifies the DSCP to assign
to the incoming frame.
Note It is not possible to classify traffic based on the markings performed by an input QoS policy. In the
Catalyst 4500 platform, the input and output QoS lookup happen in parallel, and therefore, input marked
DSCP value cannot be used to classify traffic in the output QoS policy.
Note It is not possible to classify traffic based on "internal DSCP." The "internal DSCP" is purely an internal
classification mechanism used for all packets to determine transmit queue and transmit CoS values only.
For information on the maps described in this section, see the “Mapping Tables” section on page 27-14.
For configuration information on port trust states, see the “Configuring the Trust State of Interfaces”
section on page 27-46.
