32-38
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
OL-8915-03
Chapter 32 Configuring QoS
Configuring Standard QoS
Configuring the CoS Value for an Interface
QoS assigns the CoS value specified with the
mls qos cos
interface configuration command to untagged
frames received on trusted and untrusted ports.
Beginning in privileged EXEC mode, follow these steps to define the default CoS value of a port or to
assign the default CoS to all incoming packets on the port:
To return to the default setting, use the
no mls qos cos
{
default-cos
|
override
} interface configuration
command.
Configuring a Trusted Boundary to Ensure Port Security
In a typical network, you connect a Cisco IP Phone to a switch port, as shown in
Figure 32-12 on
page 32-36
, and cascade devices that generate data packets from the back 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 802.1Q header. The header
contains the VLAN information 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 switch 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 which
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface
interface-id
Specify the port to be configured, and enter interface configuration mode.
Valid interfaces include physical ports.
Step 3
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 packet is untagged, the default CoS value becomes the packet CoS
value. 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 packet and to apply the default port CoS value to
the port on all incoming packets. By default, CoS override is disabled.
Use the
override
keyword when all incoming packets on specified ports
deserve higher or lower priority than packets entering from other ports.
Even if a port was previously set to trust DSCP, CoS, or IP precedence,
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
the packet is modified with the default CoS of the port at the ingress
port.
Step 4
end
Return to privileged EXEC mode.
Step 5
show mls qos interface
Verify your entries.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
