Voice and Data Vlans

  • 0
  • 1
  • Question
  • Updated 1 month ago
  • Answered
I need to setup a switch (X460P) to be able to use a VOIP Phone (Polycom) and to be able to use a PC also.  The PC MIGHT be plugged into the phone, or there may not be a phone at all, just a PC plugged into a port.

All ports on the switch would need this ability.
So far, I would do this:
Create Vlan Voice tag 10
Config Voice IPAddress
Config voice add ports 1-48 tag
config vlan default ipaddress
config vlan default add ports 1-48
ena ipforward voice
ena ipforward default
Config iproute add default

I would configure DHCP for each vlan

Now comes my real question.
How does the switch know that I'm plugging in a phone, rather than a PC (or printer or other device). ?   I want the voice vlan to get DHCP from the scope I create for Voice, but if a PC gets plugged in, I want DHCP from the data scope I create.  
How it know?
Photo of Malcolm


  • 120 Points 100 badge 2x thumb

Posted 4 years ago

  • 0
  • 1
Photo of Patrick Voss

Patrick Voss, Alum

  • 11,714 Points 10k badge 2x thumb
It knows based off the tagging of the port. A PC will not send tagged traffic therefore it will be received on the untag VLAN of that port. Depending on how a phone is configure it should pass tagged traffic. Depending on the phone it should default tagged.
Photo of McClane

McClane, Employee

  • 410 Points 250 badge 2x thumb
Depending on the Polycom model, you should be able to use LLDP to assign the VLAN ID... I would search through Polycom documentation and verify their LLDP support and then read through the LLDP section of the EXOS user guide.
Photo of Patrick Voss

Patrick Voss, Alum

  • 11,714 Points 10k badge 2x thumb
Here is an article that explains the configuration for lldp with a polycom phone:


Hope this helps!
Photo of Tavares Belmont

Tavares Belmont

  • 638 Points 500 badge 2x thumb

Usually the DHCP server phone PABX or Telefone central...every time when the device ask for ip address inside SVI, the dhcp server through option 82, reply with correct ip address for each device...Usually ip phones have vlan id default depends of vendor, and many central have feature for not delivery ip address for PC just for phones too, you can use this option on you central.

Photo of Malcolm


  • 120 Points 100 badge 2x thumb
Thanks everybody.  This has been helpful!
Photo of Marcus Florido

Marcus Florido

  • 382 Points 250 badge 2x thumb
There are many different ways to do this, but the basic underlying structure will remain the same.  You'll configure the switchport to be a member of an untagged VLAN (with it's associated DHCP scope) for the computer, and then tag the "voice" VLAN (with a different DHCP scope associated with it) for the phone traffic.  The phone will be capable of separating the traffic based on the VLAN tag, and since you will be plugging the computer into the phone jack, you can let the phone do the magic for you.  On an Enterasys switch the port commands would look something like this, where VLAN 300=data_VLAN, and VLAN 400=voice_VLAN:

set port vlan ge.1.1 300 no-modify egress
set vlan egress 400 ge.1.1 tagged

The XOS will be similar, and look something like this:

configure voice_VLAN add ports 1 untagged
configure data_VLAN add ports 1 tagged

I am admittedly less familiar with XOS (for now).  Plug the phone into the switch, and your computer into the phone, and you should be on your way.
Hello Marcus!

We have 2 Enterasys (C3G124-48, 48 ports) in our network, the rest are Cisco.

We are implementing Asterisk with IP telephones (cisco 7911) so we have a somewhat complicated scenario.

We have a voice Vlan (303)
We have a data vlan (1)

How do we configure the 44 ports of the Enterasys (1-44)?

The Trunk nodes for the voice vlan were configured with:

set vlan egress 303 ge.1.45-48 tagged

The show vlan portinfo command shows us

Port VLAN Ingress Egress
                          Filter Vlan

ge.1.45 1 N tagged: 1,303
ge.1.46 1 N tagged: 1,303
ge.1.47 1 N tagged: 1,303
ge.1.48 1 N tagged: 1,303

How do we configure the nodes so that the phone takes the address of the dhcp (172.15.1.x) and the PC of the user that is in the port of the phone take the DHCP Ip (172.16.x.x, data segment with vlan 1)?

We appreciate your valuable help.

The Cli commands that you give up lines did not work with us.
Photo of Ronald Dvorak

Ronald Dvorak, Embassador

  • 49,866 Points 20k badge 2x thumb
The commands are for switches with XOS operating system - the C3 uses EOS.

Take a look into this KB article for EOS...

Thank you so much! They were already configured and working.

Thanks for the data and the support!
Photo of Renne Stuart

Renne Stuart

  • 260 Points 250 badge 2x thumb
This will not work unless you either manually vlan tag the phone or set up dhcp scope options to give the phone it's tag or preferred option to set up Lldp. The tag and un tag in your example for xos is the wrong way round as well.
Photo of Marcus Florido

Marcus Florido

  • 100 Points 100 badge 2x thumb
Thank you for catching this, Renne.  Dyslexia.  It's a disease horrible! 

Let me correct this for the OP:

configure vlan "data_VLAN" add ports 1 untagged
configure vlan "voice_VLAN" add ports 1 tagged

Many find that setting up the phones/switches in this manner is simpler this way (note that I did not say better).  Since the OP wanted to know how the switch (not the DHCP server) differentiated between the traffic destined to the two devices, I simply mentioned how the segregation works (VLAN tagging).