On
the Cisco Nexus device, the packet buffer per port is 640KB.
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 1. Cisco Nexus 5500
Platform Default Buffer Allocations Per Port
Traffic Class
|
Ingress Buffer (KB)
|
Class-fcoe
|
79.360
|
User-defined no-drop with an MTU less than 2240
|
79.360
|
User-defined no-drop class with an MTU greater than 2240
|
90.204
|
Tail drop traffic class
|
22.720
|
Class-default
|
All of the remaining buffer (470 with default QoS configuration)
|
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.
Note |
Each new class
requires an additional 29.76KB, so the exact amount of buffer that is left in
the class default equals 470 minus the buffer used by other qos-groups minus
29.76KB times the number of qos-groups.
|
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