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sonny.wigmore
Beginner

QOS Classes

                   Hello All

Wondering if I can have some help with QOS classes and their behaviours.

I have a network with 2 main classes, AF1 which I know is Bulk Data and Default class. The AF1 class has 9mb of the 10mb circuit applied and default class has only 900k. I am seeing thousands of random drops and tail drops on the default class.

When looking at the policy maps with the #show policy-map interface    command I can see no packets falling within the AF1 class. Would this bandwidth then fall within the default class?

Your help would be much appreciated, I can provide some outputs if neccessary.

Many thanks

3 REPLIES 3
Joseph W. Doherty
Hall of Fame Expert

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.

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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

Most likely, the drops you report in the default class are due to bandwidth oversubscription and/or less than optimal parameter settings.  If the former, a long term solution might require providing additional bandwidth, which might be provided by a path with additional physical bandwidth or perhaps by taking bandwidth from lower priority class flows.  If the latter, parameter tuning might mitigate.

The default class contains all flows not in any other defined classes.  You might have bulk data that isn't properly marked, and if it's not, it will fall into the class default.

Thanks for the reply Joseph I had done a bit more research and found that this is the case. I imagine that a better long term solution would be to change the bandwidth around so it was more accurate, just for the sake of records. As it does seem a bit silly to apply such bandwidth to an unused class even if it does fall into default after.

Thanks

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 realize, by default, unused class bandwidth is used by other classes.  So, even if the bulk class is defined 90% of the bandwidth, but if it's using none, that bandwidth is available to classes.

As to making bandwidth allocation more "accurate", you could, but the (non-LLQ) allocations are minimum bandwidth guarantees.  For typical rate bulk traffic, even a single flow might consume 100%, so for those, you allocate what you consider the minimum needed to "reserve" the bandwidth for other more "important" traffic.

I often use as low as 1% for bulk traffic.  Again, as classes can often take advantage of unused bandwidth, I'll often see the bulk class consuming 90% of my bandwidth, but with only a 1% guarantee, effectively the 1% is available bandwidth, i.e. all other traffic transmits before bulk, but bulk then uses the remaining available bandwidth.