From: Scott Morris (swm@emanon.com)
Date: Tue Jul 06 2004 - 16:03:49 GMT-3
DTP is a separate process indicative of the "dynamic" mode that the port is
in by default. As stated, the phone discovers the voice vlan through a CDP
addition, which it will then tag. PC traffic through the other end is
untagged on the access VLAN.
If you have a dynamic port, and this is the VLAN that untagged traffic is
sent on, then it may very well work out that way where your PC looks like
the switch is trying to form a trunk with it. While I haven't tried using a
NIC on the PC that will respond in kind, I feel pretty sure technically that
you won't actually establish a dot1q trunk through the IP Phone. ;) That
would cause some definite confusion in the network.
If you are setting up an IP Phone on the 3550, there is no need to
specifically configure a trunk due to this semi-intelligent behavior and
capability of multi-vlan ports. However, if you are connecting an IP phone
to an XL-based switch, or the NM-16-Esw on a 3700 router (Hint, these may be
coming?) then you must specifically set the port in trunking mode, or the
magic won't work.
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
JNCIP, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
swm@emanon.com/smorris@ipexpert.net
http://www.ipexpert.net
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Dan
Shechter
Sent: Tuesday, July 06, 2004 2:51 PM
To: TiuN Hong Leng
Cc: ccielab@groupstudy.com
Subject: Re: switchport voice vlan
TiuN Hong Leng wrote:
>Hi,
>
>Yes thanks Dan, But why the document says it should be configured on
>access ports?
>
>
>
>>>
>>>
>>>
>>>
>>When connection to Cisco phone there is no need to configure manual
>>trunking.
>>The Cisco phone uses CDP for several purposes:
>>
>> * The switch can learn that it is connected to a Cisco phone
>> * The switch can tell the phone what VLan tag use for voice, or tell
>> the phone to use dot1p to "tag" voice frames
>>
>>So with Cisco phones no need to configure trunks.
>>
>>HTH,
>>Dan
>>
>>
>
>
>
>
>
I dont sure why, but I think it because it wants to signal the PC with DTP
that it's connected to access port and not try to form a trunk which the
phone wont be able to bridge.
You can configure it with out 'sw access' but I havn't tried it with a
phone, the switch will accpet the commands.
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