QoS Policy based on defined bandwidth

Unanswered Question
Dec 22nd, 2009

Is it possible to create QoS policies based on a defined bandwidth?  I have the following policy-map applied to an interface that is 100M.  This 100M interface connects to an ISP managed router that is not smart enough to do the QoS policies we need.  The other interface of the ISP router is 3.08M NxT1.  My solution is to let my 2811 router perform the QoS but I need a way for the interface to prioritize bandwidht based on 3.0Mbps not 100Mbps.

policy-map att-cos-107
class voice
    priority percent 60
class control
    bandwidth percent 16
class critical
    bandwidth percent 12
class class-default
    fair-queue
     random-detect dscp-based

Is it as simple as adding the bandwidth statement to the interface?

interface FastEthernet0/0
ip address 10.255.31.4 255.255.255.0
bandwidth 3080

duplex full
speed 100

I have this problem too.
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Laurent Aubert Tue, 12/22/2009 - 12:04

Hi,

Yes it should work ;-) But be aware that 3.08M of T1 (PPP or HDLC based) is not 3.08 ethernet due to the overhead difference. The idea is to have always your FastEthernet interface to be congestioned (where you have your QoS policy) before your WAN link.

Ethernet header is longer so you should be able to configure a higher value than 3.08M to be closer to your actual WAN bandwidth but if you try to be too close you could have QoS flapping issue or not having QoS at all as you never reach your congestion point.

Another way to do it would be to use Hierarchichal QoS with a parent shaper.

HTH

Laurent.

daniel.nocito Wed, 12/23/2009 - 12:42

Great idea with to use hierarchical QoS with a parent shaper.  I altered my policy as below.  Unfortunately I am still seeing some latency with voice traffic in the voice queue when the line is congested.   Any ideas?

policy-map rg-cos-queue
class voice
  priority percent 20
class control
  bandwidth percent 32
class critical
  bandwidth percent 24
class class-default
  fair-queue
  random-detect dscp-based

policy-map rg-cos
class class-default
  shape average 3000000
  fair-queue
  random-detect dscp-based
  service-policy rg-cos-queue

#show policy-map interface fa0/0
FastEthernet0/0

  Service-policy output: rg-cos

    Class-map: class-default (match-any)
      6660429 packets, 1839471409 bytes
      5 minute offered rate 211000 bps, drop rate 0 bps
      Match: any
      Traffic Shaping
           Target/Average   Byte   Sustain   Excess    Interval  Increment
             Rate           Limit  bits/int  bits/int  (ms)      (bytes)
          3000000/3000000   18750  75000     75000     25        9375

        Adapt  Queue     Packets   Bytes     Packets   Bytes     Shaping
        Active Depth                         Delayed   Delayed   Active
        -      0         6660082   1838976112 133073    163962630 no
      Queueing
        Flow Based Fair Queueing
        Maximum Number of Hashed Queues 256
        (total queued/total drops/no-buffer drops) 0/0/0
         exponential weight: 9

   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
   af32       0/0               0/0              0/0           28      40  1/10
   af33       0/0               0/0              0/0           24      40  1/10
   af41       0/0               0/0              0/0           32      40  1/10
   af42       0/0               0/0              0/0           28      40  1/10
   af43       0/0               0/0              0/0           24      40  1/10
    cs1       0/0               0/0              0/0           22      40  1/10
    cs2       0/0               0/0              0/0           24      40  1/10
    cs3       0/0               0/0              0/0           26      40  1/10
    cs4       0/0               0/0              0/0           28      40  1/10
    cs5       0/0               0/0              0/0           30      40  1/10
    cs6  150273/10083987        0/0              0/0           32      40  1/10
    cs7       0/0               0/0              0/0           34      40  1/10
     ef 3731525/777951043       0/0              0/0           36      40  1/10
   rsvp       0/0               0/0              0/0           36      40  1/10
default 2778631/1051436379      0/0              0/0           20      40  1/10


      Service-policy : rg-cos-queue

        Class-map: voice (match-any)
          3731525 packets, 777951043 bytes
          5 minute offered rate 175000 bps, drop rate 0 bps
          Match: ip dscp ef (46)
            3731524 packets, 777951043 bytes
            5 minute rate 175000 bps
          Queueing
            Strict Priority
            Output Queue: Conversation 136
            Bandwidth 20 (%)
            Bandwidth 600 (kbps) Burst 15000 (Bytes)
            (pkts matched/bytes matched) 7004/1409103
            (total drops/bytes drops) 0/0

        Class-map: control (match-any)
          0 packets, 0 bytes
          5 minute offered rate 0 bps, drop rate 0 bps
          Match: ip dscp af41 (34)
            0 packets, 0 bytes
            5 minute rate 0 bps
          Queueing
            Output Queue: Conversation 137
            Bandwidth 32 (%)
            Bandwidth 960 (kbps)Max Threshold 64 (packets)
            (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0

        Class-map: critical (match-any)
          0 packets, 0 bytes
          5 minute offered rate 0 bps, drop rate 0 bps
          Match: ip dscp af31 (26)
            0 packets, 0 bytes
            5 minute rate 0 bps
          Match: access-group 103
            0 packets, 0 bytes
            5 minute rate 0 bps
          Queueing
            Output Queue: Conversation 138
            Bandwidth 24 (%)
            Bandwidth 720 (kbps)Max Threshold 64 (packets)
            (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0

        Class-map: class-default (match-any)
          2928904 packets, 1061520366 bytes
          5 minute offered rate 35000 bps, drop rate 0 bps
          Match: any
          Queueing
            Flow Based Fair Queueing
            Maximum Number of Hashed Queues 128
        (total queued/total drops/no-buffer drops) 0/347/0
             exponential weight: 9

   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
   af32       0/0               0/0              0/0           28      40  1/10
   af33       0/0               0/0              0/0           24      40  1/10
   af41       0/0               0/0              0/0           32      40  1/10
   af42       0/0               0/0              0/0           28      40  1/10
   af43       0/0               0/0              0/0           24      40  1/10
    cs1       0/0               0/0              0/0           22      40  1/10
    cs2       0/0               0/0              0/0           24      40  1/10
    cs3       0/0               0/0              0/0           26      40  1/10
    cs4       0/0               0/0              0/0           28      40  1/10
    cs5       0/0               0/0              0/0           30      40  1/10
    cs6  150273/10083987        0/0              0/0           32      40  1/10
    cs7       0/0               0/0              0/0           34      40  1/10
     ef       0/0               0/0              0/0           36      40  1/10
   rsvp       0/0               0/0              0/0           36      40  1/10
default 2778284/1050941082    307/437997        40/57300       20      40  1/10

Laurent Aubert Wed, 12/23/2009 - 19:38

Hi Daniel,

The default Tc is set to 25ms. You could try to reduce it to 10ms by configuring a Bc of 30000 in your shaper.

Also you can remove the fair-queue and the WRED from the parent class-default.

HTH

Laurent.

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