HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 475

QoS for Traffic Directed to the CPU, QoS Configuration Guidelines and Limitations

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QoS Configuration Guidelines and Limitations QoS for Traffic Directed to the CPU QoS for Traffic Directed to the CPU The switch automatically applies QoS policies to traffic that is directed to the CPU to ensure that the CPU is not flooded with packets. Control traffic, such as BPDU frames, is given higher priority to ensure delivery. QoS Configuration Guidelines and Limitations Switch resources (such as buffers, virtual output queues, and egress queues) are partitioned based on the default and user-defined system classes. Cisco NX-OS automatically adjusts the resource allocation to accommodate the configured system classes. To maintain optimal switch performance, follow these guidelines when configuring system classes and policies: • If less than four Ethernet classes are defined, up to two of these classes can be configured as no-drop classes. If more than three Ethernet classes are defined, only one of these classes can be configured as a no-drop class. The default drop class is counted as an Ethernet class. • If priority flow control is enabled on an Ethernet interface, pause will never be applied to traffic with a drop system class. PFC does not apply pause to drop classes and the link-level pause feature is never enabled on an interface with PFC. • All FCoE traffic on an Ethernet interface is mapped to one no-drop system class. By default, this class is associated with CoS value 3, although you can configure a different value. If you configure standard Ethernet traffic to use the same CoS value as FCoE, this traffic is still mapped to the FCoE system class and the switch will apply priority flow control on the FCoE CoS value. • When a Cisco Nexus 2148T Fabric Extender is connected and in use, data traffic should never be marked with a CoS value of 7. CoS 7 is reserved for control traffic transiting the Fabric Extender. Note Type qos policies can be activated only on Cisco Nexus 5000 Series interfaces and Cisco Nexus 2000 Series Fabric Extender interfaces. Type qos policies on Fabric Extender fabric interfaces or Fabric Extender fabric EtherChannel interfaces are ineffective, though the Cisco NX-OS CLI does not reject the configuration. We recommend that you do not configure type qos policy-maps on Fabric Extender fabric interfaces or Fabric Extender fabric EtherChannel interfaces to avoid wasting hardware resources. When configuring EtherChannels, note the following guidelines: • The service policy configured on an EtherChannel applies to all member interfaces. • The priority flow control configured on an EtherChannel applies to all member interfaces. Configuring System Classes Configuring Class Maps You can create or modify a class map with the class-map command. The class map is a named object that represents a class of traffic. In the class map, you specify a set of match criteria for classifying the packets. You can then reference class maps in policy maps. OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 429

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QoS for Traffic Directed to the CPU
The switch automatically applies QoS policies to traffic that is directed to the CPU to ensure that the CPU is
not flooded with packets. Control traffic, such as BPDU frames, is given higher priority to ensure delivery.
QoS Configuration Guidelines and Limitations
Switch resources (such as buffers, virtual output queues, and egress queues) are partitioned based on the
default and user-defined system classes. Cisco NX-OS automatically adjusts the resource allocation to
accommodate the configured system classes.
To maintain optimal switch performance, follow these guidelines when configuring system classes and policies:
• If less than four Ethernet classes are defined, up to two of these classes can be configured as no-drop
classes. If more than three Ethernet classes are defined, only one of these classes can be configured as
a no-drop class. The default drop class is counted as an Ethernet class.
• If priority flow control is enabled on an Ethernet interface, pause will never be applied to traffic with a
drop system class. PFC does not apply pause to drop classes and the link-level pause feature is never
enabled on an interface with PFC.
• All FCoE traffic on an Ethernet interface is mapped to one no-drop system class. By default, this class
is associated with CoS value 3, although you can configure a different value. If you configure standard
Ethernet traffic to use the same CoS value as FCoE, this traffic is still mapped to the FCoE system class
and the switch will apply priority flow control on the FCoE CoS value.
• When a Cisco Nexus 2148T Fabric Extender is connected and in use, data traffic should never be marked
with a CoS value of 7. CoS 7 is reserved for control traffic transiting the Fabric Extender.
Type qos policies can be activated only on Cisco Nexus 5000 Series interfaces and Cisco Nexus 2000
Series Fabric Extender interfaces. Type qos policies on Fabric Extender fabric interfaces or Fabric Extender
fabric EtherChannel interfaces are ineffective, though the Cisco NX-OS CLI does not reject the
configuration.
We recommend that you do not configure type qos policy-maps on Fabric Extender fabric interfaces or
Fabric Extender fabric EtherChannel interfaces to avoid wasting hardware resources.
Note
When configuring EtherChannels, note the following guidelines:
• The service policy configured on an EtherChannel applies to all member interfaces.
• The priority flow control configured on an EtherChannel applies to all member interfaces.
Configuring System Classes
Configuring Class Maps
You can create or modify a class map with the
class-map
command. The class map is a named object that
represents a class of traffic. In the class map, you specify a set of match criteria for classifying the packets.
You can then reference class maps in policy maps.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
429
QoS Configuration Guidelines and Limitations
QoS for Traffic Directed to the CPU