Network Queue QoS Policies
244
Quality of Service Guide
3HE 11014 AAAC TQZZA Edition: 01
mbs
Syntax mbs percent
no mbs
Context config>qos>network-queue>queue
Description This command specifies the relative amount of the queue space for the maximum buffers for
a specific ingress network adapter card forwarding class queue or egress network port
forwarding class queue. The value is entered as a percentage.
The Maximum Burst Size (MBS) value is used by a queue to determine whether it has
exhausted its total allowed buffers while enqueuing packets. Once the queue has exceeded
its maximum amount of buffers, all packets are discarded until the queue transmits a packet.
A queue that has not exceeded its MBS size is not guaranteed that a buffer will be available
when needed or that the packet’s RED/WRED slope will not force the discard of the packet.
Setting proper CBS parameters and controlling CBS oversubscription is one major safeguard
to queue starvation (when a queue does not receive its fair share of buffers). Another is
properly setting the RED/WRED slope parameters for the needs of the network queues.
The MBS size can sometimes be smaller than the CBS. This will result in a portion of the CBS
for the queue to be unused and should be avoided.
The no form of this command returns the MBS size for the queue to the default for the
forwarding class.
Default Table 41 lists the mbs forwarding class defaults.
Table 41 MBS Forwarding Class Defaults
Forwarding Class Forwarding
Class Label
Unicast Queue Multicast Queue
Queue ID Default MBS Queue ID Default MBS
Network-Control nc 8 2.5 16 2.5
High-1 h1 7 2.5 15 2.5
Expedited ef 6 5 14 5
High-2 h2 5 5 13 5
Low-1 l1 4 2.5 12 2.5
Assured af 3 5 11 5
Low-2 l2 2 5 10 5
Best-Effort be 1 5 9 5
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