Can qos cause issues on a LAN

[carl_townshend]

Hi all

On a switch which has 1 gig uplinks to my core, and then 100 meg wan layer 2 links to another site, if I enable qos and then just trust the packets coming in, can this cause any issues. ? I haven't enabled and priority queue on the ports just mls qos trust dscp .

We have a server that's been having issues transferring files across the 100 meg wan links even though they are only 10% utilised, can the qos config above cause any issues?

And also to my core do I need to enable priority queue or just mls qos trust dscp ?

Cheers

[Joseph W. Doherty]

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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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Posting

What devices?

2960/3560/3750 all decrease their buffer resources (because of allocations per egress queues) when you enable QoS.

Does the problem exist with QoS disabled?

[carl_townshend]

They are 3750s

I only enabled the trust qos command but with no priority queue. I haven't tested yet with qos disabled.

What are your thoughts?

Would you expect this behaviour?

Please can you elaborate?

[Joseph W. Doherty]

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

Are any of your interfaces showing drops?

re: eloborate: see https://supportforums.cisco.com/docs/DOC-8093

[carl_townshend]

Not as far as I have seen!

With qos, will it only kick in when the interface is congested?

[Joseph W. Doherty]

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

With qos, will it only kick in when the interface is congested?

(Egress) QoS - yes.