Table 59: QoS Processing and Mapping Tables
Mapping Table UsageQoS Processing
Stage
During the classification stage, QoS uses configurable mapping tables to derive a
corresponding DSCP or CoS value from a received CoS, DSCP, or IP precedence
value. These maps include the CoS-to-DSCP map and the IP-precedence-to-DSCP
map.
You configure these maps by using the mls qos map cos-dscp and the mls qos map
ip-prec-dscp global configuration commands.
On an ingress port configured in the DSCP-trusted state, if the DSCP values are
different between the QoS domains, you can apply the configurable
DSCP-to-DSCP-mutation map to the port that is on the boundary between the two
QoS domains.
You configure this map by using the mls qos map dscp-mutation global configuration
command.
Classification
During policing stage, QoS can assign another DSCP value to an IP or a non-IP packet
(if the packet is out of profile and the policer specifies a marked-down value). This
configurable map is called the policed-DSCP map.
You configure this map by using the mls qos map policed-dscp global configuration
command.
Policing
Before the traffic reaches the scheduling stage, QoS stores the packet in an egress
queue according to the QoS label. The QoS label is based on the DSCP or the CoS
value in the packet and selects the queue through the DSCP output queue threshold
maps or through the CoS output queue threshold maps. In addition to an egress queue,
the QOS label also identifies the WTD threshold value.
You configure these maps by using the mls qos srr-queue { output} dscp-map and
the mls qos srr-queue { output} cos-map global configuration commands.
Pre-scheduling
The CoS-to-DSCP, DSCP-to-CoS, and the IP-precedence-to-DSCP maps have default values that might or
might not be appropriate for your network.
The default DSCP-to-DSCP-mutation map and the default policed-DSCP map are null maps; they map an
incoming DSCP value to the same DSCP value. The DSCP-to-DSCP-mutation map is the only map you apply
to a specific port. All other maps apply to the entire switch.
Related Topics
Configuring DSCP Maps, on page 604
Queueing and Scheduling on Ingress Queues, on page 556
Queueing and Scheduling on Egress Queues
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
553
Information About QoS
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