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New Member

How to enable priority queueing in catalyst 6500 Sup720


I need to enable PQ on L2 trunk port for ingress VoIP traffic with DSCP EF set.Is the procedure related to Tx que settings..




Re: How to enable priority queueing in catalyst 6500 Sup720

Hi there

WARNING: Noob alerT! Do not deploy this unless you really really think it works but I think I covered most of the things.

(config)#mls qos

!Enable Qos Globally

(config)#mls qos trust dscp

!Tell Qos what to trust

(config)#class-map MATCH_VOIP match-all

!define the name of your class map and tell it what to match

(config-cmap)#match ip dscp *yourdscpvaluehere*

!match the dscp value you want

(config)#policy map VOIP_ON_STEROIDS

!Give the Qos policy a name

(config-pmap)#class MATCH_VOIP

!What should the policy do ? put in the name of your class map

(config-if)#service policy VOIP_ON_STERIODS in

!assign the policy to the interface you want

(config-if)#priority-group 1

!assign a priority list to the interface this enables priority queuing (was this your question?)

(config)priority-list 1 protocol ip high map VOIP_ON_STEROIDS

!configure what goes into the high priority queue

I must say here that I have used in place of the map command an accesslist and successfuly configured something similar. I just hope this works out for you. Atleast it would get you started out :)


New Member

Re: How to enable priority queueing in catalyst 6500 Sup720

Hello Kas,

I have the same voip issue a few month ago.

I think, you should consider two factor.

the first, qos capability of the module.

you can check the capability using sh intx/x capability.

the second, if you have pfc daughter card, consider mapping dscp to cos...

Please refer to the follow URL,




Re: How to enable priority queueing in catalyst 6500 Sup720


The link John provided is a MUST read.

This document is also a MUST read on QoS:

Secondly, if you have port-channels that spread across modules in the same switch, be very careful before enabling 'mls qos'. Don't do it on a production switch in the middle of the businees day. If the modules in the channel have different port queing structures 'mls qos' will disable part of the channel to keep the queueing structure consistent within the channel. The workaround is to configure 'no mls qos channel-consistency' on the Port-Channel interface.

Please rate all helpful posts.


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