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Chapter 28
Configuring QoS
Mapping DSCP or CoS Values to an Egress Queue and to a Threshold ID
You can prioritize traffic by placing packets with particular DSCPs or costs of service into certain
queues and adjusting the queue thresholds so that packets with lower priorities are dropped.
The egress queue default settings are suitable for most situations. You should change them only when
Note
you have a thorough understanding of the egress queues and if these settings do not meet your QoS
solution.
Beginning in privileged EXEC mode, follow these steps to map DSCP or CoS values to an egress queue
and to a threshold ID. This procedure is optional.
Command
Step 1
configure terminal
Step 2
mls qos srr-queue output dscp-map
queue queue-id threshold threshold-id
dscp1...dscp8
or
mls qos srr-queue output cos-map
queue queue-id threshold threshold-id
cos1...cos8
Step 3
end
Step 4
show mls qos maps
Step 5
copy running-config startup-config
To return to the default DSCP output queue threshold map or the default CoS output queue threshold
map, use the no mls qos srr-queue output dscp-map or the no mls qos srr-queue output cos-map
global configuration command.
OL-8603-04
Purpose
Enter global configuration mode.
Map DSCP or CoS values to an egress queue and to a threshold ID.
By default, DSCP values 0–15 are mapped to queue 2 and threshold 1.
DSCP values 16–31 are mapped to queue 3 and threshold 1. DSCP values
32–39 and 48–63 are mapped to queue 4 and threshold 1. DSCP values
40–47 are mapped to queue 1 and threshold 1.
By default, CoS values 0 and 1 are mapped to queue 2 and threshold 1.
CoS values 2 and 3 are mapped to queue 3 and threshold 1. CoS values 4,
6, and 7 are mapped to queue 4 and threshold 1. CoS value 5 is mapped to
queue 1 and threshold 1.
For queue-id, the range is 1 to 4.
•
For threshold-id, the range is 1 to 3. The drop-threshold percentage
•
for threshold 3 is predefined. It is set to the queue-full state.
For dscp1...dscp8, enter up to eight values, and separate each value
•
with a space. The range is 0 to 63.
For cos1...cos8, enter up to eight values, and separate each value with
•
a space. The range is 0 to 7.
Return to privileged EXEC mode.
Verify your entries.
The DSCP output queue threshold map appears as a matrix. The d1
column specifies the most-significant digit of the DSCP number; the d2
row specifies the least-significant digit in the DSCP number. The
intersection of the d1 and the d2 values provides the queue ID and
threshold ID; for example, queue 2 and threshold 1 (02-01).
The CoS output queue threshold map shows the CoS value in the top row
and the corresponding queue ID and threshold ID in the second row; for
example, queue 2 and threshold 2 (2-2).
(Optional) Save your entries in the configuration file.
Catalyst 2960 Switch Software Configuration Guide
Configuring Standard QoS
28-65
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