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Bronze

switchport voice vlan { vlan id/dot1p/untagged/none}

Hi everybody

Please consider the following scenario:

Rest of network-------Sw-f1/1-----ip phone

                                                               |

                                                               |

                                                              pc

Sw config:

Int f1/1

switchport access vlan 2

switchport voice  voice vlan 5

1)Will will vlan ip phone use for PC ?

===============================

Int f1/1

switchport access vlan 2

switchport voice vlan dot1p

2)What vlan ip phone use for voip traffic ? what vlan will  ip phone use for PC?

======================================================

int f1/1

switchport access vlan 2

switchport voice vlan untagged

3)What vlan  will ip phone use for voip traffic and PC?

My book says Ip phone will use native vlan for both voip traffic and pc.  Native vlan on a trunk is vlan 1 by default.  If ip phone does not insert dot1q for native vlan, how  can cos values be carried by voip traffic using native vlan when there is no dot1q header?

==============================================

4)int f1/1

switchport access vlan 2

switchport voice vlan none.

What vlans will ip  phone use for voip and PC ?

thanks and have a great weekend.

4 ACCEPTED SOLUTIONS

Accepted Solutions
VIP Super Bronze

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Hi Sarah

Usually the vice vlan and the data vlan for PC are in different subnets

The native vlan which is used for PC is I tagged and the voice vlan is tagged

You want to keep the data and voice in separate vlans and subnet so it is easy to apply QOS to voice vlan

It is Also a good practice

HTH

Sent from Cisco Technical Support iPhone App

Hall of Fame Super Gold

switchport voice vlan { vlan id/dot1p/untagged/none}

Depends on the manufacturer of your phone.

I've seen a large manufacturer of VoIP equipment who's phone does NOT like the "voice VLAN" tagging, instead, preferring (or recommending according to their so-called "experts") on 802.1q Trunking instead.

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Hi Sarah,

Ip phone will use vlan 5 for voip data and native vlan 2 for pc. Even though  ip phone uses native vlan 2, does it still attach 802.1q tag? ( I thought native vlan does not carry any tag or is it simply on this special kind of trunk native vlan is just the other name for data vlan , as such dot1q tag is inserted .)

Let me explain it to you by giving some scenarios.

Int f1/1

switchport access vlan 2

switchport voice  voice vlan 5

With the above config and PC just connected to the ipphone. the PC is sending packets which are not tagged. these packets will be considered as native vlan traffic since they are untagged. The interface f1/1 is a quasi trunk meaning its not a trunk but logically a trunk.

Now, lets consider that the PC is tagging packets using some software(hypothetical). It will send the tagged packets with some 802.1p markings. Now you use the command "switchport priority extend trust cos" etc on the switch to tell the phone to trust the markings coming from the PC. Now becase the packets are tagged they are not considered to be in native vlan anymore.

I think i gave you an example in one of your other posts. I connected a switch to the ipphone data port and I could see the tagged packet come thru from the other switch meaning the phone port just acts like a bridge and forwards whatever it receives across the logical trunk.

Just remember this , if the traffic is not voice traffic then its either untagged or tagged. if its untagged then its native and goes into the access vlan, if its tagged then its normal dot1q traffic.

Does this help? Please ask if you need more

HTH

Kishore

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

hi sarah,

I dont think you can use the switchport priority extend cos with the access vlan configuration. You might have to make the port to a trunk. "switchport priority extend trust" is basically telling the phone to trust the cos markings from the PC or any other device. you need tagged frames which contain the 802.1p. so using access vlan wouldn't work here in this case. The access vlan is the native vlan when it comes to the PC sending untagged frames.

HTH

Regards, Kishore

8 REPLIES
VIP Super Bronze

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Hi Sarah

Usually the vice vlan and the data vlan for PC are in different subnets

The native vlan which is used for PC is I tagged and the voice vlan is tagged

You want to keep the data and voice in separate vlans and subnet so it is easy to apply QOS to voice vlan

It is Also a good practice

HTH

Sent from Cisco Technical Support iPhone App

Bronze

switchport voice vlan { vlan id/dot1p/untagged/none}

Thanks Reza and Leolaohoo.

My intention was to undestand  how the command works

switchport voice vlan { vlan id/dot1p/untagged/none}

My book is very vague in explaining it.

Bronze

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Hi Reza

Just want to clarify few things.

On normal trunk, we say native vlan, it means the vlan for which no dot1q tag is inserted

Now let see SWf1/1--------------------ipphone-Pc

Sw:

int f1/1

switchport access vlan 2

My book says native vlan is data vlan configured on the switch in our example it is vlan 2

So if configure:

Int f1/1

switchport access vlan 2

switchport voice  voice vlan 5

Usually the vice vlan and the data vlan for PC are in different subnets

The native vlan which is used for PC is I tagged and the voice vlan is tagged

Ip phone will use vlan 5 for voip data and native vlan 2 for pc. Even though  ip phone uses native vlan 2, does it still attach 802.1q tag? ( I thought native vlan does not carry any tag or is it simply on this special kind of trunk native vlan is just the other name for data vlan , as such dot1q tag is inserted .)

thanks

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Hi Sarah,

Ip phone will use vlan 5 for voip data and native vlan 2 for pc. Even though  ip phone uses native vlan 2, does it still attach 802.1q tag? ( I thought native vlan does not carry any tag or is it simply on this special kind of trunk native vlan is just the other name for data vlan , as such dot1q tag is inserted .)

Let me explain it to you by giving some scenarios.

Int f1/1

switchport access vlan 2

switchport voice  voice vlan 5

With the above config and PC just connected to the ipphone. the PC is sending packets which are not tagged. these packets will be considered as native vlan traffic since they are untagged. The interface f1/1 is a quasi trunk meaning its not a trunk but logically a trunk.

Now, lets consider that the PC is tagging packets using some software(hypothetical). It will send the tagged packets with some 802.1p markings. Now you use the command "switchport priority extend trust cos" etc on the switch to tell the phone to trust the markings coming from the PC. Now becase the packets are tagged they are not considered to be in native vlan anymore.

I think i gave you an example in one of your other posts. I connected a switch to the ipphone data port and I could see the tagged packet come thru from the other switch meaning the phone port just acts like a bridge and forwards whatever it receives across the logical trunk.

Just remember this , if the traffic is not voice traffic then its either untagged or tagged. if its untagged then its native and goes into the access vlan, if its tagged then its normal dot1q traffic.

Does this help? Please ask if you need more

HTH

Kishore

Bronze

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Hi Kishore.

Now, lets consider that the PC is tagging packets using some  software(hypothetical). It will send the tagged packets with some 802.1p  markings. Now you use the command "switchport priority extend trust  cos" etc on the switch to tell the phone to trust the markings coming  from the PC. Now becase the packets are tagged they are not considered  to be in native vlan anymore.

so now the packets are tagged, What would be the vlan id in those tagged packets?

If we have configured

S f1/1------------------ip phone----Pc

int f1/1

switchport access vlan 2

switchport voice valn 3

switchport priority extend trust.

Thanks and have a great weekend.

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

hi sarah,

I dont think you can use the switchport priority extend cos with the access vlan configuration. You might have to make the port to a trunk. "switchport priority extend trust" is basically telling the phone to trust the cos markings from the PC or any other device. you need tagged frames which contain the 802.1p. so using access vlan wouldn't work here in this case. The access vlan is the native vlan when it comes to the PC sending untagged frames.

HTH

Regards, Kishore

Bronze

Re: switchport voice vlan { vlan id/dot1p/untagged/none}

Thanks Kishore

You are right.  switchport priority extend extend cos 3  is configured in conjuction with  mls qos commands. Good catch!

thanks and have a great weekend.

Hall of Fame Super Gold

switchport voice vlan { vlan id/dot1p/untagged/none}

Depends on the manufacturer of your phone.

I've seen a large manufacturer of VoIP equipment who's phone does NOT like the "voice VLAN" tagging, instead, preferring (or recommending according to their so-called "experts") on 802.1q Trunking instead.

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