voice vlan

[csco11063007]

What is the diff between voicevlan and aux.vlan?

Is it a must to configure the switchport as trunk while using voicevlan?

if so why?

[thisisshanky]

both r essentially the same. its called aux vlan in cat os based switches (6500). its recommended to keep voice and data separate in two vlans if the pc is plugged in through the back of phone. when you configure a port with voice vlan (aux vlan), yes the port is essentially a trunk port with dot1q from switchport to the phone.

int fa0/1

switchport voice vlan 100

switchport access vlan 101

or in Catos switches

set vlan 101 6/1

set port auxiliaryvlan 6/1 100

HTh

Sankar

PS: please remember to rate posts!

[csco11063007]

My question is pc is plugged in through the back of a phone is it a must to configure that

port as a trunk port

int fa0/1

switchport voice vlan 100

swithport mode trunk ? <--- is this command needed to configure in switch

From cisco site i got this information

Q. What is the difference between an auxiliary VLAN for the Cisco Catalyst switches and the voice VLAN for the Cisco EtherSwitch HWICs?

A. Voice VLANs require that the port be configured as a trunk port, whereas auxiliary VLANs do not. The Cisco EtherSwitch HWICs do not support auxiliary VLAN and must be configured as trunk ports for voice VLANs.

[efairbanks]

Does anyone know of an alternative to using the Auxiliaryvlan command? Fiber interfaces do not support it. I need to trunk both the data and voice VLAN to the phone,have the phone communicate via the voice vlan, and pass traffic on the data VLAN to the workstation. Thanks in advance.

[mdietrich]

on a 3560 switch I would config the switchport like this for phone with PC; am I missing something?

int fa0/1

switchport trunk encapsulation dot1q

switchport mode trunk

switchport voice vlan X

spanning tree portfast

auto qos voip cisco-phone

[efairbanks]

You need to specify a native VLAN to pass your workstation traffic, unless your workstation traffic resides in the default native VLAN (1). You can also remove the trunk commands which allow you to implement port security if desired. Traditionally, port security cannot be applied to a trunked interface.

int fa0/1

switchport access vlan XXX

switchport voice vlan XXX

switchport port-security

switchport port-security mac-address sticky

[Matthew Bryant]

I don't remember which document I pulled this from, but we had the same question a while ago, and this seemed to be the best explanation.

A Cisco IP Phone can use an 802.1Q trunk to transport packets from two VLANs: the voice VLAN (voice packets) and the native VLAN (data packets, untagged). By default, a Cisco IP Phone transports both its voice packets and the data packets from a connected device over the native VLAN. All data is untagged.

After a switch has been configured to instruct an IP Phone to support a VVID number, the switch and phone must use an 802.1Q trunk between them. On Catalyst 3500XL switches, trunk negotiation is not supported and the 802.1Q trunk must be manually configured. The IP Phone will automatically use an 802.1Q trunk on its end of the connection.

For Catalyst 4000 and 6000 switches, a special-case 802.1Q trunk is negotiated with the IP Phone using CDP and the DTP. Once the phone is detected, the switch port becomes a vlan2-access port, supporting only the two voice and data VLANs. The port won't be shown in trunking mode from the show trunk command. In fact, it doesn't matter which trunking mode (auto, desirable, on, or off) is configured on the port?the special trunk will be negotiated through the DTP. Be sure that the trunk is not configured using the nonegotiate keyword, as DTP messages will not be sent or received and the trunk will not be automatically established.

The Spanning Tree Protocol (STP) is automatically supported over the IP Phone trunk as well. The show spantree command displays the STP state for both of the VLANs on the trunk.

[rases]

Hi all,

we have a problem with this configuration.

When we have a PC connected to an IP phone an this is connected to a Catalyst 3500XL the phone is registered and runs correctly, but the PC doesn't have connectivity.

Anyone knows wha's happening and if we've forgotten any command??

This is the config of the port with IP phone and PC:

switchport access vlan 50 (data vlan)

switchport trunk encapsulation dot1q

switchport trunk native vlan 61

switchport mode trunk

switchport voice vlan 250 (voice vlan)

spanning-tree portfast

and this is the config of the Gigabit port:

switchport trunk encapsulation dot1q

switchport trunk native vlan 61

switchport mode trunk

if we connect only the PC to this port with the followinf config, it runs correctly:

switchport access vlan 50

spanning-tree portfast

Thanks in advance.

[paolo bevilacqua]

Hi,

ports with a phone and PC should be configure as:

switchport mode access

switchport access vlan 50

switchport voice vlan 250

That's it.

Please rate this post if useful!

[rases]

With the config you've told me the PC runs correctly but the phone doesn't have connectivity or it doesn't get an IP address from DHCP...

[mchandak]

What is the phone model you have ?? And is your DHCP server in the same VLAN as the IP Phones, incase it is in a different vlan, then you will have to configure the default gateway of this vlan to send DHCP requests to ur DHCP Server using "ip helper-address "

[rases]

the model is 7912G. The DHCP server is in different VLAN but is reachable.

[paolo bevilacqua]

mchandak is correct, when DHCP server is in a different VLAN, you must configure "ip helper address". The configuration "trunk" is for trunks and not for phones.

[rases]

but the "ip helper addres" must be configured in the interface or in globlal mode??

[mchandak]

it has to be used on the interface which is working as the default gateway for this vlan/subnet