[c-nsp] WRED thresholds and queue-limit

[tkacprzynski at SpencerStuart.com]

Hello,
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
correctly? 

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
 GigabitEthernet0/0

  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
      Queueing
      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