QoS Class-maps

Question

Trying to understand the class-default for marking
I have the concept of Identify traffic with ACLs
Classify traffic for marking with class-maps
Mark traffic with policy-maps
the policy-map will always have a default-class for unaccounted traffic in the policy-maps
what I don't quite understand is that the there is not a class-map class-default
when servicing the "policy" the class-maps are referenced with "class A" "class B" "class class-default"
when looking for the matches on class class-default there is no reference class-map to go to....
I figured I have to accept this logic means if  traffic was not specifically matched by the collection of class-maps in the config the IOS can assume the traffic would have been/is class-default.
i had put a config together to classify certain traffic as CS0, like SNMP... i wanted to force traffic there as well as having all unaccounted traffic being classified CS0.
but from what i read if i don't have snmp matched in any class-map in the config then this traffic would find itself in
policy-map XXX
     class class-default
     set ip precedence 0
even though class-default does not exist as class-map class-default

Answer 1

Hi,
You want to mark some traffic as CS0? and then count that traffic? but you won't know which traffic had CS0 imposed or was natively IPP 0 like all data traffic not specifically marked.
the class class-default exists just do a show class-map and you'll see it, it is the IOS which creates it.
Doing a show policy-map interface will show you which class-map was matched.