This is my scnerio:
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.
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
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.
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.