From: Asawilunda (asawilunda@googlemail.com)
Date: Wed Dec 03 2008 - 08:46:42 ARST
Cisco calls this a Multi-Vlan access port, and NOT a trunk port. if it were
a trunk port, according to Cisco, it would flood all vlans configured on the
switch out to the phone. As you probably know already, a port configured for
voice Vlan does not flood out all Vlans to the phone, just the voice vlan
frames (tagged) and the data frames ( untagged ). Below is a copy and paste
from Cisco - ARCHv2-
Multiservice switches supports a new parameter for IP Telephony support that
makes the access port a multi-VLAN access port. The new parameter is called
an auxiliary VLAN. Every
Ethernet 10/100/1000 port in the switch is associated with two VLANs
- A Native VLAN for data service that is identified by the port VLAN
identifier or PVID
- An Auxiliary VLAN for voice service that is identified by the voice
VLAN identified or VVID.
- During the initial CDP exchange with the access switch, the IP phone
is configured with a VVID.
- The IP phone also supplied with a QoS configuration using Cisco
Discovery Protocol. Voice traffic is separated from data, and supports a
different trust boundary.
Data packets between the multiservice access switch and the PC or
workstation will be on the
native VLAN. All packets going out on the native VLAN of a 802.1q port are
sent untagged by
the access switch. The PC or workstation connected to the IP phone usually
sends untagged
packets.
Voice packets will be tagged by the IP phone based on the Cisco Discovery
Protocol
information from the access switch.
*The multi-VLAN access ports are not trunk ports, even though the hardware
is set to dot1q trunk*. The hardware setting is used to carry more than two
VLANs, but the port is still considered an access port that is able to carry
one native VLAN and the Auxiliary VLAN. The
*switchport host* command can be applied to a multi-VLAN access port on the
access switch.
On Wed, Dec 3, 2008 at 10:27 AM, Carlos G Mendioroz <tron@huapi.ba.ar>wrote:
> Mark,
> 802.1Q defines a frame format, which is capable of carrying both a QoS
> mark (COS) and a VlanID.
>
> We kind of agreed in calling trunk a link which has a multivlan capability.
> I'm basically saying that you can setup a port to honour
> the COS marking w/o paying attention to VlanID.
>
> I got sidetracked by my sneefer port filtering vlan tags (Intel pro,
> changed OS recently, had to reinstall driver, play with registry et al.)
> I'll post my findings shortly.
>
> -Carlos
>
> Mark Stephanus Chandra @ 2/12/2008 21:34 -0200 dixit:
>
> HI Carlos,
>>
>> Your statement is still confusing, having 802.1p without a trunk, but it
>> carried by dot1q. dot1q is a trunk right ?
>>
>> Someone in the group once said that even we configure the port switchport
>> mode access, but when we add voice vlan configuration, the port change to
>> a
>> trunk actually.
>> Is it true ?
>>
>> Any lab result ?
>>
>> Regards
>>
>> Mark Stephanus Chandra
>> IT Consultant
>>
>> -----Original Message-----
>> From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar] Sent: 02 Desember 2008
>> 18:01
>> To: Radioactive Frog
>> Cc: mark.chandra@gmail.com; ccielab@groupstudy.com
>> Subject: Re: Voice vlan
>>
>> 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/1
>> 2.2_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
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>>
>>>
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>>
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>> _______________________________________________________________________
>>
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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
>
>
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