Cisco Systems 3750E Manual De Usuario
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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 36 Configuring QoS
Configuring Standard QoS
With the trusted setting, you also can use the trusted boundary feature to prevent misuse of a
high-priority queue if a user bypasses the telephone and connects the PC directly to the switch. Without
trusted boundary, the CoS labels generated by the PC are trusted by the switch (because of the trusted
CoS setting). By contrast, trusted boundary uses CDP to detect the presence of a Cisco IP Phone (such
as the Cisco IP Phone 7910, 7935, 7940, and 7960) on a switch port. If the telephone is not detected, the
trusted boundary feature disables the trusted setting on the switch port and prevents misuse of a
high-priority queue. Note that the trusted boundary feature is not effective if the PC and Cisco IP Phone
are connected to a hub that is connected to the switch.
high-priority queue if a user bypasses the telephone and connects the PC directly to the switch. Without
trusted boundary, the CoS labels generated by the PC are trusted by the switch (because of the trusted
CoS setting). By contrast, trusted boundary uses CDP to detect the presence of a Cisco IP Phone (such
as the Cisco IP Phone 7910, 7935, 7940, and 7960) on a switch port. If the telephone is not detected, the
trusted boundary feature disables the trusted setting on the switch port and prevents misuse of a
high-priority queue. Note that the trusted boundary feature is not effective if the PC and Cisco IP Phone
are connected to a hub that is connected to the switch.
In some situations, you can prevent a PC connected to the Cisco IP Phone from taking advantage of a
high-priority data queue. You can use the switchport priority extend cos interface configuration
command to configure the telephone through the switch CLI to override the priority of the traffic
received from the PC.
high-priority data queue. You can use the switchport priority extend cos interface configuration
command to configure the telephone through the switch CLI to override the priority of the traffic
received from the PC.
Beginning in privileged EXEC mode, follow these steps to enable trusted boundary on a port:
To disable the trusted boundary feature, use the no mls qos trust device interface configuration
command.
command.
Enabling DSCP Transparency Mode
The switch supports the DSCP transparency feature. It affects only the DSCP field of a packet at egress.
By default, DSCP transparency is disabled. The switch modifies the DSCP field in an incoming packet,
and the DSCP field in the outgoing packet is based on the quality of service (QoS) configuration,
including the port trust setting, policing and marking, and the DSCP-to-DSCP mutation map.
By default, DSCP transparency is disabled. The switch modifies the DSCP field in an incoming packet,
and the DSCP field in the outgoing packet is based on the quality of service (QoS) configuration,
including the port trust setting, policing and marking, and the DSCP-to-DSCP mutation map.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
cdp run
Enable CDP globally. By default, CDP is enabled.
Step 3
interface interface-id
Specify the port connected to the Cisco IP Phone, and enter interface
configuration mode.
configuration mode.
Valid interfaces include physical ports.
Step 4
cdp enable
Enable CDP on the port. By default, CDP is enabled.
Step 5
mls qos trust cos
mls qos trust dscp
Configure the switch port to trust the CoS value in traffic received from the
Cisco IP Phone.
Cisco IP Phone.
or
Configure the routed port to trust the DSCP value in traffic received from
the Cisco IP Phone.
the Cisco IP Phone.
By default, the port is not trusted.
Step 6
mls qos trust device cisco-phone
Specify that the Cisco IP Phone is a trusted device.
You cannot enable both trusted boundary and auto-QoS (auto qos voip
interface configuration command) at the same time; they are mutually
exclusive.
interface configuration command) at the same time; they are mutually
exclusive.
Step 7
end
Return to privileged EXEC mode.
Step 8
show mls qos interface
Verify your entries.
Step 9
copy running-config startup-config
(Optional) Save your entries in the configuration file.