The default QoS configuration for the Nexus 5000 platform creates the class-fcoe and class-default.
The show queuing interface command displays the configured qos-group and the ingress buffer allocated for
each qos-group.
Buffering and Queue Limits on the Cisco Nexus Device
On the Nexus 5500 platform, the packet buffer per port is 640KB. The Nexus 5548P, Nexus 5548UP, and the
Nexus 5596UP switch share the same buffer architecture. The Nexus 5500 platform implements Virtual Output
Queueing (VOQ) and ingress buffer architecture with the majority of the buffer allocated at ingress. The
architecture allows the switch to store packets at multiple ingress ports when there are multiple ports sending
traffic to one egress port which causes congestion.
The following default buffer allocations per port exist for the Cisco Nexus 5500 Platform:
Table 10: Cisco Nexus 5500 Platform Default Buffer Allocations Per Port
Ingress Buffer (KB)
Traffic Class
79.360
Class-fcoe
79.360
User-defined no-drop with an MTU less than 2240
90.204
User-defined no-drop class with an MTU greater than
2240
22.720
Tail drop traffic class
All of the remaining buffer (470 with default QoS
configuration)
Class-default
The default buffer allocation varies depending on the type of class. For example, if you create a regular tail
drop traffic class the default allocation is 22.7KB, unless you specify a larger size using the
queue-limit
command.
To increase the ingress buffer space available to a user-created qos-group, from a network-qos policy-map,
use the
queue-limit
command.
In addition to ingress buffer allocated for each user-created qos-group there is an additional 29.76KB buffer
required at egress for each qos-group.
With the default QoS configuration, all of the available buffer (470KB) is allocated to the class-default. When
you create a new qos-group, the buffer required for the new qos-group will be taken away from class-default.
The amount of buffer that is left for class-default equals 470 minus the ingress buffer used by other qos-groups
minus 29.76KB and times the number of qos-groups.
Each new class requires an additional 29.76KB, so the exact amount of buffer that is left in the class default
equals 478 minus the buffer used by other qos-groups minus 18.880KB times the number of qos-groups.
Note
The default QoS policy for the Cisco Nexus device does not create class-fcoe and does not reserve buffer and
qos-group for FCoE traffic.
The
show queuing interface
command can display the amount of ingress buffer allocated for each qos-group
Cisco Nexus 5000 NX-OS Quality of Service Configuration Guide, Release 5.1(3)N2(1)
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Configuring Queuing and Flow Control
Buffering and Queue Limits on the Cisco Nexus Device
