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New Member

Bandwidth available when classifying

I'm having trouble with my queuing config and was hoping that someone could take a look please? I have created the following:

class-map match-any critical

match protocol rtp

class-map match-any priority

match access-group 180

policy-map queue

class critical

priority percent 35

class priority

bandwidth percent 40

class class-default

fair-queue

random-detect dscp-based

And then:

int s0/0/0:0

service-policy output queue

Then when I do a show int, the available bandwidth goes to 1kpbs (formerly 1536kbps)

Output queue: 0/1000/64/916 (size/max total/threshold/drops)

Conversations 0/2/256 (active/max active/max total)

Reserved Conversations 2/2 (allocated/max allocated)

Available Bandwidth 1 kilobits/sec

This is a 2mbps serial interface on a 2800 running Version 12.3(8r)T7.

So, why would the available bandwidth become 1kpbs? Is available bandwidth referring to the bandwidth that's left for the class-default? Or the bandwidth availble to the critical & priority class?

I should also mention that it wouldn't allow me to increase the priority bandwidth to above 35%. Also, bandwidth is configured as 2048 on the interface.

Any help gratefully recieved!

Thanks,

J

  • Voice over IP
7 REPLIES

Re: Bandwidth available when classifying

Hi J

Can you post the output of show policy-map interface serial 0/0/0:0 here ?

regds

New Member

Re: Bandwidth available when classifying

Hi Spremkumar,

Thanks for your response. Here is the output. I have changed the values though to:

class critical 20%

class prioirty 30%

It doesn't look like it's working though:

show policy-map interface s0/0/0:0

Serial0/0/0:0

Service-policy output: queue

Class-map: critical (match-any)

0 packets, 0 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: protocol rtp

0 packets, 0 bytes

5 minute rate 0 bps

Queueing

Strict Priority

Output Queue: Conversation 264

Bandwidth 20 (%)

Bandwidth 409 (kbps) Burst 10225 (Bytes)

(pkts matched/bytes matched) 0/0

(total drops/bytes drops) 0/0

Class-map: priority (match-any)

0 packets, 0 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: access-group 180

0 packets, 0 bytes

5 minute rate 0 bps

Queueing

Output Queue: Conversation 265

Bandwidth 30 (%)

Bandwidth 614 (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)

72727 packets, 38704060 bytes

5 minute offered rate 769000 bps, drop rate 0 bps

Match: any

Queueing

Flow Based Fair Queueing

Maximum Number of Hashed Queues 256

(total queued/total drops/no-buffer drops) 3/100/0

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 26/3166 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 41/3928 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 72888/38781710 100/73423 0/0 20 40 1/10

Re: Bandwidth available when classifying

Hi,

by default 75% of configured interface bandwidth can be allocated to different classes. You have used the 75% (35+40) and thus can not increase it anymore. If you want more than 75% you need to configure "max-reservable 90" on the specific interface.

Be aware however, that you need some bandwidth for IP routing, layer2 keepalives and such as well as for default class.

The available bandwidth does not mean you can not send 100% traffic load down the interface. This 75% is only for allocation purposes. Any class could load the interface to 100% as queueing only kicks in when the interface is overloaded. Only then your 35% and 40% rules would be applied.

Regards, Martin

New Member

Re: Bandwidth available when classifying

Thanks for your response Martin. Would it be more sensible to have my 2 configured classes totally say 50% of bandwidth?

Although queueing only kicks in when the interface is overloaded, shouldn't I still see the counters in the show policy-map interface s0/0/0:0 command increase for the different classes? Or are the packets literally only inspected/classified when the interface becomes overloaded?

Thanks again,

J

Re: Bandwidth available when classifying

Hi

Queuing doesnt kickin when the interface is overlaoded . Queuing is just splitting the output interface such a way that each packets are given some priority in going out of the interface .

So if there is a match in the traffic of the class , the counters would show the increase eventhough there is one packet or 1000 packet in the queue.

regards

vanesh k

Re: Bandwidth available when classifying

Hi,

packets are only counted in queueing, if queueing kicks in if CEF switched. Any packet will be forwarded with line speed if no overload situation exists. It is only then, that the CPU of a router "sees" the packet.

Some more informations on this: "Understanding Packet Counters in show policy-map interface Output"

http://www.cisco.com/en/US/tech/tk543/tk760/technologies_tech_note09186a0080108e2d.shtml

Hope this helps! Please rate all posts.

Regards, Martin

[edit]

Whether it makes sense to use 50% ... I cannot tell you. What are the application requirements and how much traffic do you have in the respective classes? QoS here means to assign resources to applications. Unfortunately this means you need to have a more or less detailed knowledge about your applications and their network requirements.

There is no simple formula to calculate the values.

New Member

Re: Bandwidth available when classifying

Hi Martin,

Thanks for your help, it is much clearer to me now.

I guess I will have to have a good think about what percentages I would like to use.

Regards,

J

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