VoIP QoS on Cisco Catalyst Switches

Basic configuration of QoS for VoIP on Cisco Catalyst Switches

 

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1. Global mode

Cisco_VoIP_QoS# conf t
Cisco_VoIP_QoS(confi)# mls qos

 

* If ‘mls qos’ is not enabled, all DSCP value from phone won’t be stripped off.

 

2. Interface

Cisco_VoIP_QoS# conf t
Cisco_VoIP_QoS(conf)# interface x/x (Access and Trunk ports)
Cisco_VoIP_QoS(conf-if)# mls qos trust [ cos / device / dscp / ip-precedence ]
 

* Once ‘mls qos’ is enabled, without ‘mls qos trust’ on the interface all DSCP value from IP phone will be stripped off.

 

3. QoS Map

Default Value

CoS 0 = DSCP 0
CoS 1 = DSCP 8
CoS 2 = DSCP 16
CoS 3 = DSCP 24
CoS 4 = DSCP 32
CoS 5 = DSCP 40
CoS 6 = DSCP 48
CoS 7 = DSCP 56

 

If you want to change DSCP 40 to DSCP 46 for VoIP/RTP

CoS – DSCP
Cisco_VoIP_QoS# conf t
Cisco_VoIP_QoS(conf)# mls qos map cos-dscp 0 8 16 24 32 46 48 56
Cisco_VoIP_QoS(conf)# exit

Cisco_VoIP_QoS# sh mls qos maps cos-dscp

   Cos-dscp map:
        cos:   0  1  2  3  4  5  6  7
     ——————————–
       dscp:   0  8 16 24 32 46 48 56
 

DSCP –  CoS
Cisco_VoIP_QoS# conf t
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  0 to 0
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  8 to 1
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  16 to 2
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  24 to 3
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  32 to 4
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  46 to 5
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  48 to 6
Cisco_VoIP_QoS(conf)# mls qos map dscp-cos  56 to 7

 

Cisco_VoIP_QoS# sh mls qos maps dscp-cos

   Dscp-cos map:
     d1 :  d2 0  1  2  3  4  5  6  7  8  9
     —————————————
      0 :    00 00 00 00 00 00 00 00 01 01
      1 :    01 01 01 01 01 01 02 02 02 02
      2 :    02 02 02 02 03 03 03 03 03 03
      3 :    03 03 04 04 04 04 04 04 04 04
      4 :    05 05 05 05 05 05 05 05 06 06
      5 :    06 06 06 06 06 06 07 07 07 07
      6 :    07 07 07 07
 

4. Verifying

show mls qos
show mls qos interface x/x
show mls qos map cos-dscp
show mls qos map dscp-cos
show mls qos map dscp-mutation

 

5. Tips

– Most of Cisco Phone is sending DSCP, but CoS as default