[c-nsp] Default CoS

Victor Sudakov vas at mpeks.tomsk.su
Tue Apr 30 02:01:55 EDT 2013


I have enabled "mls qos" on some C3560X switches and configured 
"mls qos trust cos" on the trunk ports. Nothing more.

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? 

I have read somewhere that IOS marks IP routing traffic to DSCP CS6.
Is there some mapping between DSCP and CoS bits enabled by default?
However, there can be no question of DSCP in STP frames.

Where can I read what else is marked by default and how?

Thanks in advance for any input.

Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at sibptus.tomsk.ru

More information about the cisco-nsp mailing list