How to configure QoS on Switch

Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an equal chance of being dropped. Implementing quality of service (QoS) enables you to control bandwidth allocation to different services available in your network by classifying, policing, marking, and queuing packets. Before implementing QoS, it is crucial that you understand what traffic you are looking at and see how it flows through the network, end to end. Important on the wired side (switch):

■　Do not forget to enable QoS globally: mls qos
■　On trunks, trust Layer 2 QoS: mls qos trust cos
■　On nontrunks, trust Layer 3 QoS: mls qos trust dscp■　Tune default CoS-to-DSCP or DSCP-to-CoS mappings where necessary: mls qos map cos-dscp or mls qos map dscp-cos 
 

■　Configure a QoS policy (optional).
■　Classify traffic into classes (class-map)
■　Configure the policy for each class (policy-map)
■　Attach the policy to the interface(s).

 

 

! Configure qos on Switch !

--------------------------------------------------------------------

mls qos

mls qos map cos-dscp 0 8 16 24 32 46 48 56
mls qos map dscp-cos 24 to 3
mls qos map dscp-cos 46 to 5

do sh mls qos map

 Cos-dscp map:

 cos : 0  1  2   3   4   5   6   7

-----------------------------------------

dscp: 0  8  16  24  32  46   48  56

--------------------------------------------------------------------

 

 

 

Important for voice implementations:

• Create a QoS policy giving priority to voice (RTP) and call control (SCCP) traffic, and apply that profile to the desired interfaces.
• Be sure that RTP packets have the proper QoS markings and that other protocols are not using the same QoS markings.
• Enable Differentiated Services Code Point (DSCP) preservation on the Cisco IOS switch and/or use a QoS policy to set DSCP to EF for RTP traffic (UDP port range 16384–32767) on the Cisco IOS router.