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Tobivan_Helden_2
Beginner

QoS: make switch to trust PC's DSCP marking

Hi,

As you all know, it's possible to override 802.1p/CoS field coming from PC attached to Catalyst switch.

This is accomplished in 2 (two) ways:

- either by '(config-if)# mls qos trust extend cos <value>'

- or via '(config-if)# switchport priority extend cos <value>'

But what about to make Cisco IP Phone to trust PC's DSCP marking ? Is this possible ?

P.S.

Can you also explain, why there 2 (two) flavors of CLI to allow switch to trust to PC's 802.1p marking ?

Thanks.

3 REPLIES 3
Tobivan_Helden_2
Beginner

Sorry for mistyping.

I mean, the PC of course attached to Cisco IP PHone which in turn attached to Cisco Catalyst switch.

Tobi,

the PC basically send untagged frames to the switch, these will normally be send as CoS=0.

the following link has some scenarios for you

http://www.cisco.com/en/US/partner/products/hw/switches/ps5023/products_tech_note09186a0080883f9e.shtml#cg211

I think you will find example 6 usefull

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a.cruea1980
Participant

Tobi -

I believe there are two versions of the command for the 2 types of switches: pure layer 2 switches, and multi-layer switches.

2900 series being a pure layer 2 switch, 4500/6500 being a multi-layer switch.

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