Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010, Configuration Manual

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system needs to buffer them. However, all queues receive the same buffer allocation
by default. If the system goes to higher buffer regions, it starts dropping packets for
all queues. When the heavy weight node finally transmits, it dequeues all buffers,
but it cannot dequeue the packets that were dropped. You do not achieve the expected
bandwidth based on scheduler profile weights.
To manage buffer starvation, configure buffer weights on queues so they are in the
same ratio as the expected bandwidth for the queues. For example, if two queues
have scheduler weight (or assured-rate) in the ratio of 2:1, then set the buffer weights
to the same ratio.
To manage buffer starvation, set the maximum-committed-threshold on queues
that do not need buffering, and increase the buffer-weight for the heavily weighted
queues in the round robin.
The system calculates the correct ratio for you. Issue the show egress queue rates
command to see the ratio:
host1# show egress-queue rates brief interface fastEthernet 9/0.2
traffic forwarded aggregate minimum maximum
interface class rate drop rate rate rate
---------------------- ----------------------- --------- --------- ------- -------
ip FastEthernet9/0.2 best-effort 0 0 25000 1000000
videoTrafficClass 0 0 375000 1000000
multicastTrafficClass 0 0 925000 1000000
internetTrafficClass 0 0 50000 1000000
Total: 0 0
Queues reported: 4
Queues filtered (under threshold): 0
Queues disabled (no rate period): 0
Queues disabled (no resources): 0
Total queues: 4
The minimum rate for each queue is the approximate rate the queue achieves if all
configured queues in the line module run infinite traffic. Configure the buffer weights
in proportion to the minimum rate displayed by the system.
Related Topics
Memory Requirements for Queue and Buffers on page 19
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Configuring Queue Profiles to Manage Buffers and Thresholds on page 22
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Monitoring Forwarding and Drop Rates on the Egress Queue on page 333
Configuring Queue Profiles to Manage Buffers and Thresholds
A queue profile controls the buffering and dropping behavior of a set of egress queues
by enabling you to set the buffer weight of the queue, the drop thresholds, and the
constraints on queue lengths.
Set the queue lengths as follows:
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To oversubscribe buffer memory, set a minimum queue length.
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Configuring Queue Profiles to Manage Buffers and Thresholds
JUNOSe 11.1.x Quality of Service Configuration Guide