From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Wed Dec 03 2008 - 10:57:08 ARST
Pedals aside, it sort of works like I expected.
If you enable "voice vlan dot1p" then the switch will honour the COS
marking but will reject any frame that has a vlan is different from 0.
So, it does carry COS, but it does not honour vlan tags (actually, it
enforces it to be 0), Q.E.D.
It took me a while to test, cause new phones (java based) are reluctant
to be configured by hand (I remember that 7960's could be manually
configured) so I had to configure the phone , disable cdp, configure the
switch... and as all this goes CDP, I had to insert a hub to do the
monitoring. Still had one getting dust somewhere :)
-Carlos
Radioactive Frog @ 2/12/2008 9:55 -0200 dixit:
> I reckon, you lab it up and that will clear this up!!
>
> You said: switch is going to affect the way the switch handles the rx
> packets, so no way to see if it works
>
> the rx packet from phone to switch is not like QoS queues/inout frames.
> Switch expecting 1500 bytes frame and phone is sending 1504 (4 bytes 802.1q
> frame including 802.1p).
> How will that get through the switch?
>
> the bottom line is, a port got to be trunked on both - switch + phone to see
> COS marking. at least on the cisco catalyst switches. newer switches
> supports jambo frame and this won't be an issue passing 1504 bytes frame
> through non-trunked port.
>
> lab it up man, I'm sure that will kill the cat.
>
> hth.
> -frog
> CCIE#21569
>
>
> On Tue, Dec 2, 2008 at 10:00 PM, Carlos G Mendioroz <tron@huapi.ba.ar>wrote:
>
>> Hmm, let's clear it up (what you propose, I mean).
>> First, what you configure at the switch is not always going to
>> change the way the phone does things, and AFAIK, 802.1p as configured
>> in the switch is going to affect the way the switch handles the rx packets,
>> so no way to see if it works (wrt trunk/no trunk) by inspecting
>> packets in the link.
>>
>> I don't know what you mean by "not working if you don't activate trunk".
>> Now that we agree (I hope) that trunk := multi vlan, what I say is that
>> you can have the phone use 802.1p (riding 802.1Q frames) to do QOS marking
>> without having a trunk, i.e., having both data and voice traffic
>> on same vlan (or not using the vlan id in the 802.1Q frame to actually
>> switch the voice packet).
>>
>> I have not labbed this, but I do believe it works like that.
>> If you think it does not, I'll go ahead and lab it up.
>>
>> -Carlos
>>
>>
>> Radioactive Frog @ 2/12/2008 8:46 -0200 dixit:
>>
>>> Indeed, good discussion mate...
>>> ok lets first define the trunk :)
>>> trunk is to pass multple vlan and it increases the normal ethernet frame
>>> size [8021q tag we call that].
>>> without trunking you can't inject 802.1p in the ethernet frame.
>>>
>>> re;
>>> *switchport voice vlan *{/vlan-id | /dot1p /| /none /| /untagged}
>>>
>>>
>>>
> http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12
> .2_25_sea/configuration/guide/swvoip.html
>>> *here is what dot1p part of above command does;
>>> dot1p*Configure the Cisco IP Phone to use 802.1p priority tagging for
>>> voice traffic and to use the default native VLAN (VLAN 0) to carry all
>>> traffic. By default, the Cisco IP Phone forwards the voice traffic with an
>>> 802.1p priority of 5
>>>
>>> I think that command should** only activate once you turn the trunking on.
>>> lab it up and see if packets are being tagged by just issueing that one
>>> line (without switchport encapsulation dot1q).
>>>
>>> been there done that!!
>>>
>>> By default, the Cisco IP Phone forwards the voice traffic with an 802.1Q
>>> priority of 5
>>>
>>> that is if you don't put anything after - switchport voice vlan 100
>>> <dot1p>
>>>
>>> When I was doing my masters degree, this used to be a big topics to
>>> discuss and most people still confussed about it.
>>>
>>> Good one!!
>>>
>>>
>>>
>>> On Tue, Dec 2, 2008 at 9:26 PM, Carlos G Mendioroz
> <tron@huapi.ba.ar<mailto:
>>> tron@huapi.ba.ar>> wrote:
>>>
>>> For the strong disagreement, I guess we have to polish what we mean
>>> for "trunk".
>>>
>>> My view is a link carrying many vlans. A link with just one vlan, even
>>> if using 802.1q/p is not really a trunk (again, my view).
>>>
>>> This is in line (if not forced by) the way you actually configure
>>> cisco switches where you can enable 802.1p rx by doing
>>> (config)# switchport voice vlan dot1p
>>>
>>> -Carlos
>>>
>>> Radioactive Frog @ 2/12/2008 8:04 -0200 dixit:
>>>
>>>
>>>
>>> On Tue, Dec 2, 2008 at 8:50 PM, Carlos G Mendioroz
>>> <tron@huapi.ba.ar <mailto:tron@huapi.ba.ar>
>>> <mailto:tron@huapi.ba.ar <mailto: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
>>> <mailto:mark.chandra@gmail.com>
>>> <mailto:mark.chandra@gmail.com
>>> <mailto: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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>>>
>>> -- Carlos G Mendioroz <tron@huapi.ba.ar
>>> <mailto:tron@huapi.ba.ar> <mailto:tron@huapi.ba.ar
>>> <mailto:tron@huapi.ba.ar>>>
>>> LW7 EQI Argentina
>>>
>>>
>>>
>>> -- Carlos G Mendioroz <tron@huapi.ba.ar <mailto:tron@huapi.ba.ar>>
>>> LW7 EQI Argentina
>>>
>>>
>>>
>> --
>> Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI ArgentinaBlogs and organic groups at http://www.ccie.net
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