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WRED thresholds and queue-limit



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tkacprzynski at spencerstuart

Jan 25, 2012, 11:50 AM

Post #1 of 1 (620 views)
WRED thresholds and queue-limit

Is this a valid configuration of WRED, where the queue-limit is set to
64 packets (default), the WRED Min Threshold is 100 (packets) and Max
threshold is 400 (packets)? Would this configuration defeat the whole
purpose of using WRED, as the average queue depth will never reach 100
packets (min threshold) and tail drop at 64? Am I understanding this

Basically in my opinion the queue-limit should be set to at least what
the WRED Max Threshold is set to. If it is set to 64 while the WRED
Minimum Threshold is 100 no packets will be randomly dropped and just
tailed dropped after they reach the 64 packet size limit.

<sample output>
R1#sh policy-map int gi0/0 out

Service-policy output: test-pmap

Class-map: test1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: none
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
bandwidth 30000 kbps
Exp-weight-constant: 9 (1/512)
Mean queue depth: 0 packets
dscp Transmitted Random drop Tail drop
Minimum Maximum Mark
pkts/bytes pkts/bytes pkts/bytes
thresh thresh prob

cs3 0/0 0/0 0/0
100 400 1/10

<sample config of wred>
policy-map test-pmap
class test1
bandwidth 30000
random-detect dscp-based
random-detect dscp 24 100 400

Thank you,

Tom Kacprzynski

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