Its my understanding that the CoS value is set in the 802.1p field within an 802.1q tag. Therefore, in order to set a CoS value you need have an 802.1q trunk. So a PC would not be able to set a CoS value, unless its uplink was an 802.1q trunk port, rather than an access port.
So if the PC can't set the CoS value, why would you need to use the "switchport priority extend cos 0" ? Please correct me if I am wrong. Regards, Mike Brooks CCIE#16027 (R&S) On 7/23/08, Nick Marus <[EMAIL PROTECTED]> wrote: > Unless I misunderstand you, COS is applied to a packet and does not require > a 1q trunk. The connection between the pc and the phone is not 1q usually. > Just the connection between the phone and the switch. Most PC nic's can be > setup to mark it's packets with a cos value and effectively take priority on > your switched network over you voice and other high priority packets if the > switch is trusting and the phone is not remarking to 0. > > > Nick > > > On Wed, Jul 23, 2008 at 10:51 AM, Mike Brooks <[EMAIL PROTECTED]> wrote: > > Hi Everyone, > > > > I see that the standard practice on a switchport is to configure > > "switchport priority extend cos 0" in order to allow the ip phone to > > reset the cos value received from the PC to 0. > > > > My question is how would a PC ever set a "CoS" value if the link > > between the ip phone and the PC is not an 802.1q trunk ? > > > > Can someone please help me understand this ? The only thing I can > > think of is that the PC would somehow have to support an 802.1q trunk > > to it, a trunk would have to be dynamically established between the > > phone and PC. And, then the user would have to manipulate the CoS > > value. Is this possible with a Cisco phone ? > > > > If this is the only case this would work then you would think that > > Cisco would document these pre-requisites. Perhaps I am confused. > > > > Please help ;-) > > > > Regards, > > > > Mike Brooks > > CCIE#16027 (R&S) > > > > > > -- > Nick Marus > [EMAIL PROTECTED]
