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Cisco Systems IntelligentGigabit Ethernet Switch Modules for the IBMBladeCenter, Software Configuration Guide
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Chapter23 Co nfiguring QoS
Configuring Standard QoS
To return to the default setting, use the no mls qos cos {default-cos | override} interface configuration
command.
Configuring Trusted BoundaryIn a typical network, you connect a Cisco IP Phone to a sw itch port as shown in Figure 23-4 on
page 23-18, and cascade devices that generate data packets from the bac k of the telephone. The Cisco IP
Phone guarantees the voice quality through a shared data link by marking the CoS level of the voice
packets as high priority (CoS = 5) and by marking the data packets as low priority (CoS = 0). Traffic
sent from the telephone to the switch is typically marked with a tag that uses the IEEE 802.1Q header.
The header contains the VLAN informatio n and the class of service (CoS) 3-bit field, which is the
priority of the packet.
For most Cisco IP Phone configurations, the traffic sent from the telephone to the swi tch should be
trusted to ensure that voice traffic is properly prioritized over other types of traffic in the network. By
using the mls qos trust cos interface configuration command, you configure the switch port to w hich
the telephone is connected to trust the CoS labels of all traffic received on that port.
With the trusted setting, you also can use the trusted boundary feature t o 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 trus ted
CoS setting). By contrast, trusted boundary uses CDP to detect the pr esence 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 Ph one 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.
Step3 mls qos cos {default-cos | override} Configure the default CoS value for the port.
•For default-cos, specify a default CoS value to be assigned to a port. If
the port is CoS trusted and packets are untagged, the default CoS value
becomes the CoS value for the packet. The CoS range is 0 to 7. The
default is 0.
•Use the override keyword to override the previously configured trust
state of the incoming packets and to apply the default port CoS value to
all incoming packets. By default, CoS override is disabled.
Use the override keyword when all incoming packets on certain ports
deserve higher priority than packets entering from other ports. Even if
a port was previously set to trust DSCP, this command overrides the
previously configured trust state, and all the incoming CoS values are
assigned the default CoS value configured with this command. If an
incoming packet is tagged, the CoS value of th e packet is modified with
the default CoS of the port at the egress port.
Step4 end Return to privileged EXEC mode.
Step5 show mls qos interface Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose