bandwidth Percentage under CBWFQ. Packets dropping

[Mohit Kumar]

Hi Community,

Need some help in understanding CBWFQ.

We have following commands on our supplier router.

class Business-1-Class

  bandwidth percent 20

  random-detect dscp-based

  set ip dscp af31

This is 10 MB link so we are giving 2 MB for this traffic. Under link non-congestion state we are seeing drops under this class. Supplier says that bandwidth percentage puts limit on the class, so this traffic can only use 2 MB and any traffic above 2 MB will be dropped even if link overall is not congested. We have hardly crossed 6 MB ever so this link overall has never been over utilized.

As per my understaning as we are not using policing so this class should use the unused bandwidth from other classes. 20% is the minimum granted in case of link congestion but service provider has some other understanding.

Any help/clarification is appreciated.

Regards,

Mohit Kumar

[Aaron Harrison]

Hi

Can you show your show policy interface output, and your config?

Aaron

[Mohit Kumar]

Hi Aaron,

Here is the output. Presently these are no drops under business classes as service provider had cleared the counters.

this is the exact wording from our provider "once QoS established the Bandwidth reserved for Business Class and Premium it will be the maximum that it can reach independently of being more Bandwidth available in other classes"

In my understanding above holds true for Premium class but not for business classes.

policy-map main

class class-default

  shape average 10000000

  service-policy Queue-CE-Manual

policy-map Queue-CE-Manual

class Premium-Class

  police rate percent 40

  priority

  set ip dscp ef

class Business-1-Class

  bandwidth percent 20

  random-detect dscp-based

  set ip dscp af31

class Business-2-Class

  bandwidth percent 20

  random-detect dscp-based

  set ip dscp af21

class Business-3-Class

  bandwidth percent 5

  random-detect dscp-based

  set ip dscp af11

class Management-Routing-Class

  bandwidth percent 5

  set ip dscp af41

class class-default

  bandwidth percent 10

  random-detect dscp-based

  set ip dscp default

========

show policy-map interface fa4
 FastEthernet4 

  Service-policy output: main

    Class-map: class-default (match-any)
      1207352167 packets, 141744941514 bytes
      30 second offered rate 19000 bps, drop rate 0 bps
      Match: any 
      Queueing
      queue limit 64 packets
      (queue depth/total drops/no-buffer drops) 0/58/0
      (pkts output/bytes output) 1207338368/141140363065
      shape (average) cir 10000000, bc 40000, be 40000
      target shape rate 10000000

      Service-policy : Queue-CE-Manual

        queue stats for all priority classes:
          
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/0/0
          (pkts output/bytes output) 87747511/6208901163

        Class-map: Premium-Class (match-any)
          87747548 packets, 6208903873 bytes
          30 second offered rate 2000 bps, drop rate 0 bps
          Match: access-group name Premium-Classify
            87747548 packets, 6208903873 bytes
            30 second rate 2000 bps
          police:
              rate 40 %
              rate 4000000 bps, burst 125000 bytes
            conformed 87747548 packets, 6208903873 bytes; actions:
              transmit 
            exceeded 0 packets, 0 bytes; actions:
              drop 
            conformed 2000 bps, exceed 0 bps
          Priority: Strict, burst bytes 1500, b/w exceed drops: 0
          
          QoS Set
            dscp ef
              Packets marked 87747548

        Class-map: Business-1-Class (match-any)
          46561083 packets, 14617915237 bytes
          30 second offered rate 0 bps, drop rate 0 bps
          Match: access-group name Business-1-Classify
            46561084 packets, 14617915237 bytes
            30 second rate 0 bps
          Queueing
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/0/0
          (pkts output/bytes output) 46561081/14617913821
          bandwidth 20% (2000 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
            
            af31    46561082/14617914957      0/0              0/0                 32            40  1/10
          QoS Set
            dscp af31
              Packets marked 46561084

        Class-map: Business-2-Class (match-any)
          2132 packets, 189233 bytes
          30 second offered rate 0 bps, drop rate 0 bps
          Match: access-group name Business-2-Classify
            2132 packets, 189233 bytes
            30 second rate 0 bps
          Queueing
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/0/0
          (pkts output/bytes output) 2132/189233
          bandwidth 20% (2000 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
            
            af21        2132/189233          0/0              0/0                 32            40  1/10
          QoS Set
            dscp af21
              Packets marked 2132

        Class-map: Business-3-Class (match-any)
          2423509 packets, 220609213 bytes
          30 second offered rate 0 bps, drop rate 0 bps
          Match: access-group name Business-3-Classify
            2423509 packets, 220609213 bytes
            30 second rate 0 bps
          Queueing
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/0/0
          (pkts output/bytes output) 2423509/220609213
          bandwidth 5% (500 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
            
            af11     2423509/220609213       0/0              0/0                 32            40  1/10
          QoS Set
            dscp af11
              Packets marked 2423509

        Class-map: Management-Routing-Class (match-any)
          1496230 packets, 956175255 bytes
          30 second offered rate 0 bps, drop rate 0 bps
          Match: access-group name Management-Routing-Classify
            1496230 packets, 956175255 bytes
            30 second rate 0 bps
          Queueing
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/0/0
          (pkts output/bytes output) 1492353/243966920
          bandwidth 5% (500 kbps)
          QoS Set
            dscp af41
              Packets marked 1492353

        Class-map: class-default (match-any)
          1069121724 packets, 119741149725 bytes
          30 second offered rate 16000 bps, drop rate 0 bps
          Match: any 
          Queueing
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/58/0
          (pkts output/bytes output) 1069111781/119848782649
          bandwidth 10% (1000 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
            
            default1069111783/119848785892     58/79221          0/0                 20            40  1/10
          QoS Set
            dscp default
              Packets marked 1069060031

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Do you know what device and IOS this is being done on?

Usually, as you note, non-LLQ bandwidth statements do not implicitly police or shape, they just set a minimum bandwidth guarantee.  I.e. such classes can normally use additional bandwidth, if it's available.

In the stats you've posted, I see no drops under Business-Class-1.  I do see some under class-default, but very, very few relative to total egress packets for that class.

BTW, I see WRED being used, which I often recommend against, as it's not quite as simple to use optimally as it often seems.  Also, if your hand-off is Ethernet, and your CIR is 10 Mbps, you would be better served by running the interface at 10 Mbps and stop using the shaper.  Lastly, it looks like default queue depths are being used, and for 10 Mbps across a WAN, they might be too shallow.

[Mohit Kumar]

Hi Joseph,

Thanks for your post.

Its Cisco 881, Version 15.1(4)M6.

On another location it is Cisco CISCO1941/K9, Version 15.1(4)M4, with same set of commands. There also provider said that one class will not share ununsed bandwidth from other classes.

There are no drops as counters were cleared and very randomly we have seen drops on these classes.

let me put my question another way. This is exactly where i am getting confused.

this is 10 MB circuit.
Lets say there is no traffic on this circuit.
Business class 1 starts sending traffic and it goes beyond 2 MB, says 3 MB. There is still no other traffic on the circuit.
Then by looking at configurations given, will Business class 1 use the remaining unused 8 MB bandwidth (for this 1 MB extra) or will any exceeding traffic above 2 MB will be straight away dropped.

Here my understanding is that Business class 1 should use the available bandwidth from other classes but service provider says that it will not.

Regards,

Mohit Kumar

[Joseph W. Doherty · Accepted solution]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Unless something has changed within your IOS version, my expectation would be Business Class 1 could use all 10 Mbps, if it were the only class traffic.

[Mohit Kumar]

Thank you Joseph.

Appreciate your help in getting this clarified.