[c-nsp] Default CoS

Saku Ytti saku at ytti.fi
Tue Apr 30 02:26:00 EDT 2013

On (2013-04-30 13:01 +0700), Victor Sudakov wrote:
> In Wireshark I can see that some packets generated by the switches
> themselves have some non-default CoS values. E.g. OSPF hello packets
> and PIM messages have the cos value of 6 in the 802.1Q header, STP
> frames have the value of 7 etc etc.
> Why does this happen and where is it documented? 

This is canonical use of CoS/Prec values. 7 is network control, 6 is
internetwork control.

This is not exactly what you're looking for, as it's probably auto-qos

It's not very good idea to implement QoS without some idea of your goals.
At very least you should decide how many classes you need to discriminate
your traffic into (the fewer you can live with, the better, if you're not
running QoS now, 2 might be prudent)

Especially in small Catalysts just turning MLS QoS on pretty much
invariably makes your life worse than what it was.

This is must-read document for surviving 3560/3750 QoS, I'm hoping good
deal of it is valid in X world, but I don't know for sure:


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