Cisco Nexus 9000 Series Configuration Manual page 113

Configuring Queuing and Scheduling
• The FEX QoS system level queuing policy does not support WRED, queue-limit, shaping, or policing
features.
• The FEX QoS system level queuing policy does not support multiple priority levels.
• Assigning a high alpha value on a Cisco Nexus 9200 Series switch uses more than the expected 50% of
the available buffer space.
Assigning a lower alpha value (7 or less) assures the usage of the expected 50% of the available buffer
space.
• For Cisco Nexus 9200 Series switches when a static queue limit is configured on a queue, both the static
configured limit and the dynamic limit are calculated using the dynamic threshold (alpha value). (NX-OS
7.0(3)I3(1) and later releases)
• Maximum queue occupancy for Leaf Spine Engine (LSE) enabled switches are limited to 64K cells
(~13MB).
Buffer-boost
The buffer-boost feature enables the line card to use extra buffers. This capability is enabled by default on
line cards such as the N9K-X9564PX.
• The command to enable the buffer-boost feature is buffer-boost.
• The command to disable the buffer-boost feature is no buffer-boost.
Generally, Cisco recommends not to disable the buffer-boost feature. However, disabling the buffer-boost is
necessary when there is a need to port channel two different member ports from N9K-X9636PQ based line
cards and N9K-X9564PX based line cards. However, Cisco does not recommend to port channel such a
configuration between ACI capable leaf line cards and standalone line cards.
Note Line cards like the N9K-X9636PQ and similar, do not offer the buffer-boost feature.
Order of Resolution
The following describes the order of resolution for the pause buffer configuration and the queue-limit for a
priority-group.
• Pause Buffer Configuration
The pause buffer configuration is resolved in the following order:
• Queue-limit for Priority-Group
The queue-limit for a priority-group is resolved in the following order:
◦ Interface ingress queuing policy (if applied and pause buffer configuration specified for that class).
◦ System ingress queuing policy (if applied and pause buffer configuration specified for that class).
◦ System network-QoS policy (if applied and pause buffer configuration specified for that class).
◦ Default values with regards to the speed of the port.
◦ Interface ingress queuing policy (if applied and queue-limit configuration specified for that class).
Cisco Nexus 9000 Series NX-OS Quality of Service Configuration Guide, Release 7.x
Guidelines and Limitations
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