Mls Qos Trust - Cisco Catalyst 3750 Command Reference Manual

Chapter 2 Catalyst 3750 Switch Cisco IOS Commands
If the CoS is trusted, the CoS field of the packet is not modified, but the DSCP can be modified
(according to CoS-to-DSCP map) if the packet is an IP packet.
The trusted boundary feature prevents security problems if users disconnect their PCs from networked
Cisco IP phones and connect them to the switch port to take advantage of trusted CoS settings. You must
globally enable the Cisco Discovery Protocol (CDP) on the switch and on the port connected to the IP
phone. If the phone is not detected, trusted boundary disables the trusted setting on the switch port and
prevents misuse of a high-priority queue. If you configure the trust setting for DSCP or IP precedence,
the DSCP or IP precedence values in the incoming packets are trusted. If you configure the mls qos cos
override interface configuration command on the switch port connected to the IP phone, the switch
overrides the CoS of the incoming voice and data packets and assigns the default CoS value to them.
For an inter-QoS domain boundary, you can configure the port to the DSCP-trusted state and apply the
DSCP-to-DSCP-mutation map if the DSCP values are different between the QoS domains.
Classification using a port trust state (for example, mls qos trust [cos | dscp | ip-precedence] and a
policy map (for example, service-policy input policy-map-name) are mutually exclusive. The last one
configured overwrites the previous configuration.
Examples This example shows how to configure a port to trust the IP precedence field in the incoming packet:
Switch(config)# interface gigabitethernet2/0/1
Switch(config-if)# mls qos trust ip-precedence
This example shows how to specify that the Cisco IP phone connected on a port is a trusted device:
Switch(config)# interface gigabitethernet2/0/1
Switch(config-if)# mls qos trust device cisco-phone
You can verify your settings by entering the show mls qos interface privileged EXEC command.
Related Commands Command
mls qos cos
mls qos dscp-mutation
mls qos map
show mls qos interface
78-16181-01
Description
Defines the default CoS value of a port or assigns the default CoS to all
incoming packets on the port.
Applies a DSCP-to DSCP-mutation map to a DSCP-trusted port.
Defines the CoS-to-DSCP map, DSCP-to-CoS map, the
DSCP-to-DSCP-mutation map, the IP-precedence-to-DSCP map, and the
policed-DSCP map.
Displays QoS information.
Catalyst 3750 Switch Command Reference

mls qos trust

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