QoS in 2960X, drop threshholds and buffer allocations

[Chewbakka1]

Hi,

Are there any guidelines for how to set the drop threshholds and how to calculate buffer allocation for different scenarios?

Is it strictly neccessary to adjust these, or will the defaults values work?

[Mark Elsen]

 - You may find this presentation useful :

                   https://www.ciscolive.com/c/dam/r/ciscolive/apjc/docs/2015/pdf/BRKRST-2501.pdf

 M.

[Joseph W. Doherty]

There are lots and lots of guidelines.  The problem though, and likely reason there are so many (and they keep changing), it's difficult for "one size" to fit all.

Generally, if you don't have enough bandwidth there will be congestion and with congestion, if enough of it, drops.  QoS allows us to prioritize dequeuing and drops.

If you need to prioritize and selectively drop, what's important to you?

When you can answer that question, you can select, or create, a QoS policy to meet your goals.

It may be your 2960X's default QoS policy is optimal for your needs.  Or, your 2960X's AutoQoS policy might be optimal for your needs.

In my experience, either of those default policies will "protect" "typical" VoIP usage, but beyond that they are a real crapshoot.

BTW, within the 2960 series, it can be difficult to avoid buffer exhaustion since those switches don't provide a lot of buffer RAM.