Cisco Catalyst 3750-X Command Reference

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Catalyst 3750-X and 3560-X Switch Command Reference
OL-29704-01
Chapter 2 Catalyst 3750-X and 3560-X Switch Cisco IOS Commands
mls qos trust
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.
If the DSCP is trusted, the DSCP field of the IP packet is not modified. However, it is still possible that
the CoS value of the packet is modified (according to DSCP-to-CoS map).
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 or DSCP settings.
You must globally enable the Cisco Discovery Protocol (CDP) on the switch and on the port connected
to the IP phone. If the telephone is not detected, trusted boundary disables the trusted setting on the
switch or routed 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.
Note The switch supports IPv6 port-based trust with the dual IPv4 and IPv6 Switch Database Management
(SDM) templates. You must reload the switch with the dual IPv4 and IPv6 templates for switches
running IPv6.
Related Commands 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 Description
mls qos cos Defines the default CoS value of a port or assigns the default CoS to all
incoming packets on the port.
mls qos dscp-mutation Applies a DSCP-to DSCP-mutation map to a DSCP-trusted port.
mls qos map 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.
show mls qos interface Displays QoS information.

Cisco Catalyst 3750-X Specifications

General

Switching Capacity	160 Gbps
Stacking Bandwidth	64 Gbps
Max Stacking Units	9
Layer Support	Layer 2 and Layer 3
Form Factor	Rack-mountable
DRAM	256 MB
Flash Memory	64 MB
Model	Cisco Catalyst 3750-X Series
Ports	24 or 48 10/100/1000 Ethernet ports
Uplink Interfaces	4 SFP or 2 SFP+
Features	StackWise Plus, EnergyWise
Image	IP Base or IP Services
Operating Temperature	0 to 40°C
Operating Humidity	10 to 85% noncondensing