Policy Map without any policer,shaping or other actions

[OBD]

Hi,
 I wonder that how switches treat packets that classified by DSCP. For instance I've one switch and I'll apply input or output service policy with only class-map and there is only marking action in my policy-map . Does switch give priority to classified packets by looking their DSCP priority or just marking my packets without any prioritize ? 

In brief, I want to know that if marking affect prioritize forwarding or is marking packets only useful for taking action for helping network device know which package to take action for.

Thank You


Standard IP access list VOIP
10 permit 0.0.0.0, wildcard bits 255.255.255.0

Class Map match-any VOIP_CLASS (id 1)
Match access-group name VOIP

Policy Map VOIP-POLICY
Class VOIP_CLASS
set dscp ef

[Joseph W. Doherty · Accepted solution]

What happen varies.

Assuming switch's QoS is active (some require you to enable QoS, especially older series), often switches have a default treatment based on either L2 CoS tags or L3 ToS (DSCP) tags.  If fact, on some of the older series of small switches you cannot define an egress policy, egress queue selection is determined by CoS or DSCP queue mappings (again either by default or as configured).