Re: QoS question

Hi Carlos,

Thanks for your prompt answer.
As I really needed to know what is the exact behavior in this case I have
tested it using a 3560 switch and a cisco phone.
The original IOS on the switch (1-2 years old) didn't even permit the
service-policy input command on the interface at the same time with "mls qos
trust device cisco-phone".After I upgraded to the latest 3560 IOS,
12.2(53)SE, the behavior changed dramatically. Now I was permitted to put
the two commands on the same interface and after capturing some traffic it
seems the phone DSCP EF marking is not overwritten by the policy-map I
defined (which was not marking the voice packets with DSCP EF).
To summarize, below are the commands I used to configure the interface:

mls qos trust cos
mls qos trust device cisco-phone
service-policy input QoS_Marking

As this was a user/phone port those commands had the effect of letting the
DSCP EF mark of the phone to go through untouched by the policy and mark the
user traffic according to the policy (seemed that "mls qos trust cos "
command didn't apply to user traffic ).

Best Regards,

Adrian

On Thu, Apr 8, 2010 at 12:52 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:

> Adrian,
> ip traffic is always marked with some code, that should give you a clue.
> But if it does not, then it depends on the logic of the policy, but
> you can remark if you will. In your terms, the policy has precedence.
>
> "mls qos trust device" only disables the wiping of the incoming mark.
>
> It's a litle more complicated than that in fact. You need to have
> "mls qos trust dscp" in place, and that initializes the internal QoS
> marking to that of the incoming IP dscp. Then if "trust device" is
> added, the initialization is replaced with 0 if the connected device
> is not a cisco phone. Then comes your policy to change whatever, and
> last and option to leave the initial marking alone when sending.
> To top it, this is architecture dependent.
>
> HTH,
> -Carlos
>
> Lazar Adrian @ 8/04/2010 6:29 -0300 dixit:
> > Hi guys,
> >
> > I have a simple QoS implementation with one policy-map marking the
> traffic
> > inbound coming from a user or IP phone (I have a general port config, so
> > same port config no matter if a PC or phone connects to it).
> > Now, my question is related to the precedence of "mls qos trust device
> > cisco-phone" and "service-policy QoS_Marking inbound" commands. What I
> want
> > to know and I haven't found this information anywhere is, if my phone
> sends
> > DSCP EF marked traffic will the policy-map mark it down ? So the matter
> > resumes to what command has precedence over the other.
> >
> > Thank you,
> >
> > Adrian
> >
> > PS: Disregard the previous mail, I accidentally hit the send button too
> > early :)
> >
> >
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>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina

Blogs and organic groups at http://www.ccie.net
Received on Fri Apr 09 2010 - 15:10:37 ART