From: Radioactive Frog (pbhatkoti@gmail.com)
Date: Tue Dec 02 2008 - 08:04:17 ARST
On Tue, Dec 2, 2008 at 8:50 PM, Carlos G Mendioroz <tron@huapi.ba.ar> wrote:
> Well, not quite.
> Even if *link* is access, phone can mark TOS.
Agreed....TOS = layer3
>
> Even if *link* is access, phone can use 802.1p to mark COS
>
strongly disagreed as 802.1p can only go with Trunk when packet length is
scratched a bit using tagging.
in other word 802.1p is part of 802.1q or 1d frame format: (3bit field of
802.1q header is used byu 802.1p).
Check the 802.1q frame header. If you don't tag it won't can't carry 1p bit.
>
> And even is *port* is admin access, it will turn stealthy to trunk
> when it discovers a (CDP enabled ?) phone is voice vlan is there:
>
> Switch#sh int f0/8 switchport
> Name: Fa0/8
> Switchport: Enabled
> Administrative Mode: dynamic desirable
> Operational Mode: static access
> Administrative Trunking Encapsulation: dot1q
> Operational Trunking Encapsulation: native
> Negotiation of Trunking: On
> Access Mode VLAN: 2 (Lab)
> Trunking Native Mode VLAN: 1 (default)
> Voice VLAN: 1 (default)
> ...
>
> (in modern switches at least, it used not to be that way)
> -Carlos
>
> Radioactive Frog @ 2/12/2008 5:41 -0200 dixit:
>
> The idea of voice vlan is phone generates ef or cs3 streams and switch
>> prioritize that all the way tilll it see's server/endpoint.
>>
>> priority field only can be read if the packet is trunked (injected extra
>> header in the frame),. If thats link from switch to phone is not trunked
>> switch wont' know what kind of frame the phone is sending.
>>
>> so back to yoru first question, if you applying 'voice vlan under
>> interface'
>> then it has to be a trunk port.
>>
>> if port is access port then phone can't mark its frames with any cos/tos
>> bits.
>>
>> hth...
>>
>> -frog
>> CCIE#21569
>>
>> On Tue, Dec 2, 2008 at 5:59 PM, <mark.chandra@gmail.com> wrote:
>>
>> Dear groups,
>>>
>>> If we said switchport voice vlan under the interface, it's mean the port
>>> become a trunk ?
>>>
>>> When we have switchport access vlan also, which one is tag with vlan
>>> header
>>> after exiting the port ? Voice vlan or data vlan ?
>>>
>>> Thanks group
>>> Sent from my BlackBerry. wireless device from XL GPRS/EDGE/3G network
>>>
>>>
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>>
>>
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> --
> Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
Blogs and organic groups at http://www.ccie.net
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