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Community Member

QOS implementation

This is my scnerio:

ip phones---->2960---->3750----->6500

I have to implement QOS for voice

What my plan is to trust the voice traffic send by ip phone on 2960:

mls qos trust cos

mls qos trust device cisco-phone

and just enable QOS on 3750 ,so when it will recieve the voice traffic with COS 5 it will not change it

and on my 6500 the external interface is gig

show queueing interface gigabitEthernet 2/7

Interface GigabitEthernet2/7 queueing strategy: Weighted Round-Robin

Port QoS is enabled

Port is untrusted

Extend trust state: not trusted [COS = 0]

Default COS is 0

Queueing Mode In Tx direction: mode-cos

Transmit queues [type = 1p3q8t]:

Queue Id Scheduling Num of thresholds


01 WRR 08

02 WRR 08

03 WRR 08

04 Priority 01

since pirority queue is assigned to COS value 5 the incoming traffic will go in that queue.

Do i have to do anything else apart from enabling QOS globally in 3750 and 6500.

Or is there a better option ?

I also have PC connected to the ip phone ,i think that the configuraion on 2960 will not

trust the data traffic since i will not use the extend command.



Community Member

Re: QOS implementation

Hi Vishwa

On the 3750 and 6500 without mls qos enabled the default behaviour is to forward the frames without changing the qos markings.

Once you enable mls qos the default behaviour is not to trust any port and remark all incoming traffic to 0.

Thus you should have mls qos trust dhcp/cos on all your switch uplink ports if you want to preserve the qos markings throughout your campus.

You also might want to implement a outbound queuing strategy on all your uplinks that bests suits your specific requirements.

I recommend you read this SRND



Community Member

Re: QOS implementation

Hi Phillip,

Thanks for the reply,will get back with the new config after reading the document.



Hall of Fame Super Gold

Re: QOS implementation

Seems like this is a purely gigabit LAN environment.

In that case, you do not need to worry about QoS at all.

Not matter how you configure things, voice will work perfectly anyway.

Community Member

Re: QOS implementation

Hi P,

I am not sure why you say that.

Since every network will have gig uplink to distribution and then to core .

This is gig on core 6500 which is 2 MB pipe.



Hall of Fame Super Gold

Re: QOS implementation

Just configure QoS on the 2 Mb then.

It is not necessary in other places.

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