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New Member

help in QoS configuration on 3750E/2960X

Hello everybody,


I would like to configure QoS in VoIP for terminal Aastra in switches Cisco (with L3). As I am not very confident in this issue, I have thought to give a priority for VoIP considering output traffic from IP telephone. The IP telephones have an IP in range, so could it be this criteria valid for assigning QoS to the VoIP packets? The criteria would be:

ip access-list extended tel_VOIP

 permit tcp any

 permit udp any


Class-map match-all VOIP

Match access-group name tel_VOIP

Policy-map VOIP

Class VOIP

Set ip dscp 32


And then for the access voip ports, I would put this:

Interface giga0/x

switchport mode access

service-policy input VIDEO

service-policy output VOIP

 switchport voice vlan 6

 switchport access vlan n

 mls qos trust dscp

 power inline consumption 5000


Also I have another policy-map configured for input traffic for video which gives it pri 32.

I would like to know if traffic with maximum priority goes by queue out nº 1 by default. And if so, if this would be enough to guarantee video and voip traffic would go by this queue, which has by default 4 Mb shaped. Our video only takes 256Kb.


Another thing is if more than 4 Mb were needed in queue out, a way to assure video and voip traffic would be to configure this queue as priority queue-out, wouldn’t it be?


Please, I do not know how to configure queues and I only want to know if this would categorize voip and video traffic with a dscp of 32.


Thank you very much.


I am a bit lost about this item. And that is why I would prefer not configuring different weights for the out queues if not necessary. Please, make me any comment. I could send you my configuration. 



Why are you trying to assign

Why are you trying to assign all VoIP traffic with DSCP 32? RTP traffic should always be EF (DSCP 46) and Signaling should be CS3 (DSCP 32). You wouldn't assign the service-policy in the "output" it would be "input". You would assign the "mls qos trust dscp" on the trunk and "mls qos trust cos" on the switchports. What CoS/DSCP markings does the Astra system assign to its phones? What exactly do you want to do on the switch, marking and policing?



HTH Regards, Yosh
New Member

hello Yahsiel,  Well, I must

hello Yahsiel, 


Well, I must have mismatched signaling value with voice traffic value. What I would like to do is marking voip traffic and then reserving a bandwith for it. 

I have investigated and voip traffic comes marked with CoS 5, so I suppose I do not have to create an access-list, I could create a class-map for voip: 


class-map VOIP

match ip precedence 5


and then reserve BW for it: 

policy-map VOIP-VIDEO

Class VOIP

priority 1000

and then I could also set this policy in all the access ports with: 


service-policy input VOIP-VIDEO

I suppose I could include in this same policy-map the marking of VIDEO traffic which is: 


  class VIDEO
    set ip dscp 32


Also as you say I will have to put in the access ports the "mls qos trust cos" and in the trunk "mls qos trust dscp". 


Do you think now this would guarantee 1 Mb for voip in the out queue? Out queue 1 has a total of 4 Mb maximum shaped so I think this would run.... 


What about "auto qos voip trust" in the interface level for all the ports? Some people tell me this run ok, but I do not know if I must configure it or not. If I configured auto qos, I think I wouldn't have to policy voip traffic. 


Thank you for your soon reply. Really!!! 

New Member

Hello Yosh, I only wanted to

Hello Yosh, 

I only wanted to say yo that it finally run without any QoS policy configured. The thing is traffic goes with COS 5, DSCP 46 for RTP and DSCP 40 for signaling. As traffic is marked, the switches have only to maintain this marking, with just: 

mls qos trust dscp on every access port and trunk port

I was a bit lost about how this run. 

Thank you anyway. 

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