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Catalyst 3750 Switch Command Reference
OL-8552-07
Chapter 2 Catalyst 3750 Switch Cisco IOS Commands
mls qos trust
mls qos trust
Use the mls qos trust interface configuration command to configure the port trust state. Ingress traffic
can be trusted, and classification is performed by examining the packet Differentiated Services Code
Point (DSCP), class of service (CoS), or IP-precedence field. Use the no form of this command to return
a port to its untrusted state.
mls qos trust [cos | device cisco-phone | dscp | ip-precedence]
no mls qos trust [cos | device | dscp | ip-precedence]
Syntax Description
Defaults The port is not trusted. If no keyword is specified when the command is entered, the default is dscp.
Command Modes Interface configuration
Command History
Usage Guidelines Packets entering a quality of service (QoS) domain are classified at the edge of the domain. When the
packets are classified at the edge, the switch port within the QoS domain can be configured to one of the
trusted states because there is no need to classify the packets at every switch within the domain. Use this
command to specify whether the port is trusted and which fields of the packet to use to classify traffic.
When a port is configured with trust DSCP or trust IP precedence and the incoming packet is a non-IP
packet, the CoS-to-DSCP map is used to derive the corresponding DSCP value from the CoS value. The
CoS can be the packet CoS for trunk ports or the port default CoS for nontrunk ports.
cos (Optional) Classify an ingress packet by using the packet CoS value. For an
untagged packet, use the port default CoS value.
device cisco-phone (Optional) Classify an ingress packet by trusting the CoS or DSCP value sent
from the Cisco IP Phone (trusted boundary), depending on the trust setting.
dscp (Optional) Classify an ingress packet by using the packet DSCP value (most
significant 6 bits of 8-bit service-type field). For a non-IP packet, the packet
CoS is used if the packet is tagged. For an untagged packet, the default port
CoS value is used.
ip-precedence (Optional) Classify an ingress packet by using the packet IP-precedence value
(most significant 3 bits of 8-bit service-type field). For a non-IP packet, the
packet CoS is used if the packet is tagged. For an untagged packet, the port
default CoS value is used.
Release Modification
12.1(11)AX This command was introduced.
12.1(14)EA1 The device cisco-phone keywords were added.
12.2(20)SE The usage guidelines were revised to describe how the switch sets the trust
state when a Cisco IP Phone is connected to a switch or routed port.
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