Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

QoS Preventing queue starvation

Hi all,

I have a question on priority queueing.
When enabling 'priority-queue out' all traffic that belongs to queue 1 will be send out immediately, before the other queues.
This has a risk of letting the other queues starve, if traffic for queue 1 is to extensive.
therefore it is probably best to rate limit traffic belonging to queue 1.

Sometimes you see something like this:

interface gigabitethernet 1/0/1 
  srr-queue bandwidth share 1 60 30 10
  srr-queue bandwidth shape 25 0 0 0
  priority-queue out

the 'srr-queue bandwidth shape 25 0 0 0' entry in the example above both limits and reserves at the same time 1/25 of the interface bandwidth for queue 1, correct?
But this does not make sense in combination with priority-queue, right?
In the manuals they say that once 'priority-queue out' has been enabled, the values for queue 1 for the 'srr-queue bandwidth share' and 'srr-queue bandwidth shape' are discarded.
So basicaly the 'srr-queue bandwidth shape 25 0 0 0' entry is useless?

Sometimes you see this:

policy-map MY-QOS
  class VOICE
    set ip dscp 46
    police 128000 8000 exceed-action drop

This polices priority traffic to 128k, but this is inbound, correct?

so It won't prevent the priority queue from starving the other queues (outbound)?
Since priority traffic can come from somewhere where it is not policed.

So how can we prevent the outbound priority queue from starving the other queues?

Thanks for your input

Everyone's tags (3)
1 ACCEPTED SOLUTION

Accepted Solutions
Super Bronze

DisclaimerThe Author of this

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

My understanding, is like yours, i.e. PQ (unlike LLQ) can stave lower classes.

So, what can you do?

Well, first, know what traffic you allow into PQ, such that (hopefully) it won't consume all the port's bandwidth.

Or, don't use PQ, just use SRR.  With the latter, you can set SRR weight to give Q1 very high relative priority (to give it nearly PQ treatment) but then you could also shape it; if needed.  (Even if you don't shape it, SRR wouldn't allow total bandwidth starvation.)

e.g.

srr-queue bandwidth share 255 6 3 1

3 REPLIES

Hi all, Does someone have

Hi all,

 

Does someone have some input on this?

 

Thanks!

Super Bronze

DisclaimerThe Author of this

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

My understanding, is like yours, i.e. PQ (unlike LLQ) can stave lower classes.

So, what can you do?

Well, first, know what traffic you allow into PQ, such that (hopefully) it won't consume all the port's bandwidth.

Or, don't use PQ, just use SRR.  With the latter, you can set SRR weight to give Q1 very high relative priority (to give it nearly PQ treatment) but then you could also shape it; if needed.  (Even if you don't shape it, SRR wouldn't allow total bandwidth starvation.)

e.g.

srr-queue bandwidth share 255 6 3 1

Thanks for your reaction

Thanks for your reaction Joseph, I wanted to be shure about this before implmenting our QoS design. 

653
Views
0
Helpful
3
Replies