System Classes; Default System Classes - Cisco Nexus 5000 Series Configuration Manual

Configuring QoS
An MQC target is an entity (such as an Ethernet interface) that represents a flow of packets. A service policy
associates a policy map with an MQC target, and specifies whether to apply the policy on incoming or outgoing
packets. This mapping enables the configuration of QoS policies such as marking, bandwidth allocation,
buffer allocation, and so on.

System Classes

The system qos is a type of MQC target. You use a service-policy to associate a policy map with the system
qos target. A system qos policy applies to all interfaces on the switch unless a specific interface has an
overriding service-policy configuration. The system qos policies are used to define system classes, the classes
of traffic across the entire switch, and their attributes. To ensure QoS consistency (and for ease of configuration),
the switch distributes the system class parameter values to all its attached network adapters using the Data
Center Bridging Exchange (DCBX) protocol.
If service policies are configured at the interface level, the interface-level policy always takes precedence
over system class configuration or defaults.
On the Cisco Nexus 5000 Series switch, a system class is uniquely identified by a qos-group value. A total
of six system classes are supported. Two of the six system classes are defaults and are always present on the
switch. Up to four additional system classes can be created by the administrator.

Default System Classes

The Cisco Nexus 5000 Series switch provides the following system classes:
• Drop system class
• FCoE system class (For the Cisco Nexus 5010 switch and the Cisco Nexus 5020 switch)
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By default, the software classifies all unicast and multicast Ethernet traffic into the default drop system
class. This class is identified by qos-group 0.
This class is created automatically when the system starts up (the class is named class-default in the
CLI). You cannot delete this class and you cannot change the match criteria associated with the default
class.
All Fibre Channel and FCoE control and data traffic is automatically classified into the FCoE system
class, which provides no-drop service.
This class is created automatically when the system starts up (the class is named class-fcoe in the CLI).
You cannot delete class-fcoe and you can only modify the IEEE 802.1p CoS value to associate with this
class. This class is identified by qos-group 1.
The switch classifies packets into the FCoE system class as follows:
◦ FCoE traffic is classified based on EtherType.
◦ Native Fibre Channel traffic is classified based on the physical interface type.
Note The optional N5K-M1404 or N5K-M1008 expansion modules provide native ½/4-Gigabit
Fibre Channel ports.
Cisco Nexus 5000 Series NX-OS Quality of Service Configuration Guide
System Classes
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