Mls qos trust dscp??? is setting my DSCP values to zero!?

Hi,
I was just doing some testing to ensure that the command 'mls qos trust dscp' is working on my 6509 switches before rolling out QoS.
Before adding any configuration I could see using wireshark that traffic from my Avaya 9608 handset was coming through with a DSCP value of 46 (as it is supposed to).
I then added the command 'mls qos' (at global level)
on examining the wireshark output this time, the DSCP value had been set to zero (i.e. it defaulted it to best effort)
I then expected by adding the commmand 'mls qos trust dscp' on the interface the phone is connected to that the DSCP value would would again be left alone?
does anybody know why this is happening?
Many thanks in advance.
Andy

Hi,
thanks for your reply.
mls qos
interface GigabitEthernet3/34
description *** DATA VLAN 35 - VOICE VLAN 34 ***
switchport
switchport trunk native vlan 36
switchport trunk allowed vlan 34,36
switchport mode trunk
mls qos trust dscp
no cdp enable
spanning-tree portfast trunk
If i don't include the global 'mls qos' command then the voice packets keep the dscp 46 value.  If I add the mls qos command this causes the switch to set the dscp values to zero.
Thanks again 
ps.  there are some other mls commands on the switch... i don't know if these could interfere but they were already on there so i'm reluctant to remove them..

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    Hi,
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    Hi,
    thanks for your reply.
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    description *** DATA VLAN 35 - VOICE VLAN 34 ***
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    Thanks again 
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  • Mls qos trust

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    =============================
    Please remember to rate useful posts, by clicking on the stars below. 
    =============================

  • Mls qos VS mls qos trust

    Hello world!
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    Disclaimer
    The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
    Liability Disclaimer
    In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
    Posting
    Generally, on many Catalyst switches, once you enable QoS, they will erase an ingress CoS/ToS markings unless your trust it or otherwise (i.e. policy) maintain it.
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    it enables QOS on the switch, without it no QOS is being used.
    Sent from Cisco Technical Support iPhone App

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