- A virtual community of network engineers
 Home  BookStore  StudyNotes  Links  Archives  StudyRooms  HelpWanted  Discounts  Login
RE: voice and native vlan posted 08/11/2004
[Chronological Index] [Thread Index] [Top] [Date Prev][Date Next] [Thread Prev][Thread Next]

There is a reference in the Cisco Catalyst QoS manual to the effect that on IOS release 12.0x, voice vlan ports had to be configured as trunk ports but that release 12.1 does not require trunk configuration.



-----Original Message-----
From: Lord, Chris 
Sent: Wednesday, August 11, 2004 10:12 AM
To: gladston@xxxxxxxxxx; ccielab@xxxxxxxxxxxxxx
Subject: RE: voice and native vlan


The clarify, the two methods (as per Cisco DQOS Book) are:

int f0/1
	sw mode dynamic desirable
	sw access vlan 10
	sw voice vlan 100
	span portfast

int f0/1
	sw mode trunk
	sw trunk encaps dot1q
	sw voice vlan 100
	sw trunk native vlan 10
	span portfast



-----Original Message-----
From: gladston@xxxxxxxxxx [mailto:gladston@xxxxxxxxxx]
Sent: Tuesday, August 10, 2004 11:14 PM
To: ccielab@xxxxxxxxxxxxxx
Subject: voice and native vlan



I don't know why option 2 is recommended over option 1, I've seen production 
configs using both methods with Cisco phones.

However, I believe you have a mistake in your options. I think the native vlan command belongs with option 1 not option 2.

In option1, assuming a Cisco phone is used and that a PC is connected into the back of the phone, the switch uses CDP to tell the phone which voice vlan 
is in use. The phone will send voice packets to the switch using .1q frames tagged with the specified voice vlan number. The phone will send PC packets 
to the switch untagged on the native vlan. Now, when the untagged native vlan 
frames hit the switch, the switch has to decide what to do with them. If 
you've designed your network where all of the PCs are in vlan 1 (the default 
native vlan) then you don't need the "sw native vl" command. However, I'm sure you are more sensible and have the PCs in another vlan so you need to notify the switch of this using the native vlan cmd. In option 1 the "sw access vlan" command has no purpose because the port is statically configured 
as a trunk port!


If you configure:

int fa 0/0
 switchport access vlan 10
 switchport trunk encap dot1q
 switchport mode trunk
 switchport voice vlan 100

Then you do not need configure native Vlan to have data traffic goes to vlan 10. Correct?

Please help support GroupStudy by purchasing your study materials from:

Subscription information may be found at:

The information contained in this email is confidential and is intended for the recipient only. If you have received it in error, please notify us immediately by reply email and then delete it from your system. Please do not copy it or use it for any purposes, or disclose its contents to any other person or store or copy this information in any medium. The views contained in this email are those of the author and not necessarily those of Lorien plc.

Thank you for your co-operation.

Please help support GroupStudy by purchasing your study materials from:

Subscription information may be found at: