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| 8.3 |  | Classification at the Access Layer |
| 8.3.5 |  | Re-writing the CoS |

In some cases it may be desirable not to trust any CoS value that may be present in frames sourced from an edge device. For example, an office PC used for general applications, such as web browsing, e-mail, and file and print services, does not require special QoS treatment and allowing it to request higher levels of QoS may adversely affect applications, such as voice and video that really require guarantees of bandwidth and latency.

For this reason, it is possible to use the override parameter to tell the switch to ignore any existing CoS value that may be in the frame and apply the default value. This effectively disables any trust configuration that may have previously been applied to the port.

The CoS value assigned by the switch can be changed on a port-by-port basis using the interface configuration command:

> Router(config-if)#mls qos cos override

After applying this command, the switch will rewrite the CoS value for all incoming frames to the configured default value, regardless of any existing CoS value.