Queuing and scheduling are configured by creating policy maps of type
queuing that you apply to either traffic direction of an interface. You can
modify system-defined class maps, which are used in policy maps to define the
classes of traffic to which you want to apply policies.
Additional considerations are as follows:
-
Changes to system class maps
take effect immediately across all VDCs.
The specified CoS values immediately map to the new queues.
-
Changes are disruptive.
The traffic passing through ports of the specified port type
experience a brief period of traffic loss. All ports of the specified type are
affected. For example, if you change COS-to-queue mapping for the M1 10G egress
interface type, all M1 10G ports in all VDCs experience a brief disruption.
-
Performance can be impacted.
If one or more ports of the specified type do not have a queuing
policy applied that defines the behavior for the new queue, then the traffic
mapping to that queue might experience performance degradation.
-
If you change the CoS-to-queue mapping by modifying the queuing
class maps, you must ensure that a new queuing policy was applied to all ports
of that type that use the new queues.
-
If you change the DSCP-to-ingress-queue mapping by modifying the
queuing class maps, you must ensure that a new queuing policy is applied to all
ports of that type that use the new queues.
-
By default, nonused queues do not have an allocated buffer.
Allocate buffers to these queues to avoid tail drop.
-
Changes to system class-maps are made only on the default VDC.
For information about configuring policy maps and class maps, see
“Using Modular QoS CLI.”
You can configure the congestion-avoidance features, which include
tail drop and WRED, in any queue. You can configure one of the egress
congestion management features, such as priority, shaping, and bandwidth, in
output queues, and you can configure bandwidth in input queues.
We recommend that you modify the CoS value before you create a policy
map. You can modify the CoS values that are matched by device-defined class map
queues. You must assign each CoS value from 0 to 7 to one or more of the queues
for each queue type. Each CoS value is used only once in each queue type.
We recommend that you modify the DSCP value before you create a policy
map. You can modify the DSCP values that are matched by device-defined class
map queues. You must assign each DSCP value from 0 to 63 to one or more of the
queues for each queue type. Each DSCP value is used only once in each queue
type.
The system-defined policy maps default-in-policy and
default-out-policy are attached to all ports to which you do not apply a
queuing policy map. The default policy maps cannot be configured. For more
information about the default policy maps, see
Table 5.
This example shows that if you downgrade from Release 4.0(3) to
Release 4.0(2) and enter the
show running-configuration command, the input
default queuing policy has an unknown enum in the display:
switch# show running-config
version 4.0(2)
…
…
policy-map type queuing default-in-policy
class type queuing unknown enum 0
queue-limit percent 50
bandwidth percent 80
class type queuing unknown enum 0
queue-limit percent 50
bandwidth percent 20
If you copy and paste this configuration into any Cisco NX-OS release,
the device sends errors while executing all the commands starting from the
policy-map type queuing default-in-policy command.
You can ignore these errors because they do not affect the performance of the
device.