3750 Disable QoS and fix the buffers?

ryancisco01 · ‎03-27-2014

I have done a lot of research on the subject and found that the 3750 is best left without any QoS enabled. customer is complaining about a lot of dropped packets and this is affecting realtime traffic quite a bit.

What i want to do is, compelelty disable QoS and also set the buffer sizes to the most optimal settings, -or- to the maximum settings if that is better. I also want the switch to leave any dscp/QoS markings it recieves intact on all ports, so do I need to still trust dscp on every interface or just disable qos rewrite?

can anyone shed light on the commands to do so?

sh ver: WS-C3750E-24PD-S

current relevant config:

mls qos

Queueset: 1
Queue     :       1       2       3       4
----------------------------------------------
buffers   :      25      25      25      25
threshold1:     100     200     100     100
threshold2:     100     200     100     100
reserved :      50      50      50      50
maximum   :     400     400     400     400

sh mls qos interface (all interfaces have the same values as this)
GigabitEthernet1/0/1
trust state: not trusted
trust mode: not trusted
trust enabled flag: ena
COS override: dis
default COS: 0
DSCP Mutation Map: Default DSCP Mutation Map
Trust device: none
qos mode: port-based

sh mls qos

QoS is enabled
QoS ip packet dscp rewrite is enabled

Joseph W. Doherty · ‎03-28-2014

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Posting

The 3750 doesn't always operate best with QoS disabled but enabled QoS often requires customization of its QoS settings.

If you disable QoS, by default, ToS/CoS markings will be passed through the 3750 as is. Buffer configuration settings have no impact (as far as I know).

If you enable QoS, then you may very much have a need to adjust buffers settings, but one size doesn't fit all. Optimal buffer settings would depend on your intended QoS policy and your traffic.

ryancisco01 · ‎03-30-2014

Ok thanks, so from your statement you are saying I will not need to "trust dscp" on all the interfaces to pass the markings after disabling QoS?

Also what i will do is, strip out all the QoS config I can see first, then to disable qos globally I should just run the following:

no mls qos

Is that all thats needed?

Joseph W. Doherty · ‎04-01-2014

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

Yes and yes, although you don't need to actually strip out all the existing QoS statements. Once you disable QoS, they have no effect. (The configuration retains them, I believe, so they can be reused if you reactivate QoS.)