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New Member

Available Bandwidth kilobits/sec and QOS

Hey all,

I am very confused about a field I saw in the show interface command for my serial called the Available Bandwidth  kilobits/sec. I was trying to figure out a outbound discard issues and I went the route of doing the math just like this other forum post I saw which gave me 30.72 kbps of available bandwidth after QoS. However when I do a show interface it gives me  Available Bandwidth 231 kilobits/sec. I do not have the link for the post I have seen on this since I save everything to pdf. However I will post it below. I believe the router could be right since the line is not saturated so QoS has not kicked in yet but I am also right to assume these calculations if the line does get saturated? Any help will be greatly appreciated.

Original Post

Much appreciate if someone can shed some light –

In the scenario below, we have a 1Gig interface with interface bandwidth of 1G with a

• max-reserved-bandwidth 100 configured

• A nested service-policy in use.

Nested service-policy details

• Parent policy shapes to 400Mbps.

• Child policy has a VOICE-class with strict priority percent 20 example below

Policy-map parent-testing

class class-default shape average 4000000 60000 0

policy-map TESTING

class VOICE

priority percent 20

class class3

bandw idth remaining percent 40

class class2

bandw idth remaining percent 30

class class1

bandw idth remaining percent 10

class default

- Can you clarify my understanding on the behavior of this config -

Origanl Post Answer Response

Hi Sharor,

The "bandwidth remaining percent" command is an interesting command which does not give absolute

percentage values rather it provides relative percentage values allocation. Answers to your questions inline.

-------

1. The voice-class 20% is calculated off the parent policy – hence voice-class gets a max 20% of 400M = 80M

strict priority. Policed at 80M during congestions. CORRECT.

2. When there is no congestion on the link– that is say Voice-class, class3, class1, default-class have NO

packets in it; can Class2 scavenge upto 400Mbps ?? OR can Class2 go upto 320Mbps only (even though

there is nothing in voice class) Yes, it can.

2. During periods of high congestion, when all classes are congested to the full. Can you confirm when using

“bandwidth remaining percent ” command, as per the config- if –

a.Class3 will get a guaranteed minimum 128Mbps (40% of 320Mbps) Correct

b.Class2 will get a guaranteed minimum of 57.6 Mbps (30% of remaining [400-80-128]) OR

c.Class2 will get a guaranteed minimum of 96 Mbps (30%of 320Mbps) Correct

d.Class1 will get a guaranteed minimum of 13.44Mbps (10% of remaining [400-80-128-57.6]) OR

e.Class1 will get a guaranteed minimum of 32Mbps (10% of 320Mbps) Correct

3. Where does the priority percent calculates against interface bandwidth In this case ?? should the

calculations not be based on the parent policy map in this case ? Parent policy map shaper rate (in this

case, 400M)

---------

Here is an interesting example.

If Voice class is using 60Mbps, then the remaining bandwidth = 400M-60M =340M. Then, other classes will

get relative bandwidth out of this free bandwidth like Class 3 will get 40% of 340Mbps = 136Mbps.

Please go through the following link for detailed explanation.

My Issue

Available Bandwidth 1536 kbps

policy-map WAN-QOS                        

class VOICE                                        921.6 kbps

  priority percent 60                          

class INTERNETWORK-CONTROL       61.44 kbps  

  bandwidth remaining percent 10           

class CALL-SETUP                              61.44 kbps

  bandwidth remaining percent 10           

class BUSINESS-CRITICAL                  460.8 kbps

  bandwidth remaining percent 75          

  set ip dscp af21

class class-default                              30.72 kbps

  fair-queue

  random-detect

Serial0/3/0 is up, line protocol is up

  Hardware is GT96K with integrated T1 CSU/DSU

  Description:

  Internet address is

  MTU 1500 bytes, BW 1536 Kbit/sec, DLY 20000 usec,

     reliability 255/255, txload 92/255, rxload 4/255

  Encapsulation PPP, LCP Open

  Listen: CDPCP

  Open: IPCP, loopback not set

  Keepalive set (10 sec)

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters 01:12:37

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 177

  Queueing strategy: Class-based queueing

  Output queue: 0/1000/64/177 (size/max total/threshold/drops)

     Conversations  0/225/256 (active/max active/max total)

     Reserved Conversations 3/3 (allocated/max allocated)

     Available Bandwidth 231 kilobits/sec

  5 minute input rate 29000 bits/sec, 36 packets/sec

  5 minute output rate 560000 bits/sec, 59 packets/sec

     212588 packets input, 23638228 bytes, 0 no buffer

     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

     301999 packets output, 328219809 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 unknown protocol drops

     0 output buffer failures, 0 output buffers swapped out

     0 carrier transitions

     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Everyone's tags (5)
3 REPLIES
Super Bronze

Re: Available Bandwidth kilobits/sec and QOS

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

You didn't note the platform and its IOS version.  Same syntax can operate a bit differently, for example, between pre-HQF and HQF QoS.  Max-reserved-bandwidth generally unnecessary in the latter, and FQ works differently between the two.

You configs don't provide a bandwidth for class-default.  Pre-HQF supposedly, by default, sets aside 25% for class-default usage.  Also with pre-HQF with your max-reserved-bandwidth set to 100, you can explicitly allocate up to 100% in other classes, but without an explicit bandwidth setting for class-default, unsure what is "reserved" for that class.  Lastly with pre-HQF, FQ in class-default distorts other class bandwidth allocations.

Personally, I ignore whatever the stats show as "available bandwidth".  I just concern myself with total bandwidth and bandwidth ratios between classes.  For example, in your first policy, everything else being equal, if classes 3 and 1 are fighting for bandwidth, they should split it 4:1.

New Member

Re: Available Bandwidth kilobits/sec and QOS

Joseph,

Thanks for getting back to me. The Platform is 2821 and the version is12.4(25g). My question was more of is it right for me to assume that the available bandwidth for the class-default is now 30.72 kbps after my allocations and not  231 kpbs? I heard of this 25% rule for the available bandwidth, but not I am not sure what HQF or pre-HQF really is. Would you be able to give me a short explanation on this?

Thanks

Super Bronze

Re: Available Bandwidth kilobits/sec and QOS

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

Your IOS is pre-HQF.

Without an explicit bandwidth, I don't assume what class-default's bandwidth would be.  Even if I "know" how an IOS version behaves, unless it's clearly documented by Cisco, I wouldn't count on it.

If the CBWFQ stats shows you what "available bandwidth" is, you might use that.  (NB: rarely do my QoS models presuppose a specific amount of bandwidth.  I.e. just another reason I consider figuring out what it's supposed to be, isn't good use of my time.)

Short explanation: http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/qos_frhqf_support_external_docbase_0900e4b18080f624_4container_external_docbase_0900e4b1810be036.html

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