random-detect dscp-based thresholds explanation

Unanswered Question
Feb 24th, 2010

Can someone explain why the default min thresholds for dscp are larger for the higher probability AF class than the lower probability classes?

for example:

http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_q1.html#wp1052917

dscp 10 has min of 24

dscp 12 has min of 28

thanks in advance

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Sergei Vasilenko Mon, 03/01/2010 - 06:23

Hello,


Indeed, looks like this is a mistake in this table.

Should be another way around - af11(dscp10) - min thr 32, af12(dscp12) - min thr 28, af13(dscp14) - min thr 24.

Real values could be checked via "show policy-map int" on CLI, like shown at the following example link:

DSCP Value Configuration Verification: Example

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/config_wred_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1002513


Router# show policy interface Serial6/3 
 Serial6/3 

  Service-policy output: test

    Class-map: c1 (match-any)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol ip
        0 packets, 0 bytes
        5 minute rate 0 bps
      Weighted Fair Queueing
        Output Queue: Conversation 265 
        Bandwidth 20 (%)
        Bandwidth 308 (kbps)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
         exponential weight: 9
         mean queue depth: 0

dscp     Transmitted       Random drop      Tail drop    Minimum Maximum  Mark
          pkts/bytes        pkts/bytes       pkts/bytes    thresh  thresh  prob
af11          0/0               0/0              0/0           32      40  1/10
af12          0/0               0/0              0/0           28      40  1/10
af13          0/0               0/0              0/0           24      40  1/10
af21          0/0               0/0              0/0           32      40  1/10
af22          0/0               0/0              0/0           28      40  1/10
af23          0/0               0/0              0/0           24      40  1/10
af31          0/0               0/0              0/0           32      40  1/10
...

Thanks,
Sergey

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