Data and Voice in same, native vlan (1)

[andrewohanian]

I'm working on a project where I am moving some ports to a new vlan. This one particular site has user ports with data and voice in the same, native vlan (1).

interface GigabitEthernet1/0/5
switchport mode access
switchport voice vlan 1

When I added "switchport access vlan 200" the devices did not get new IPs. In fact, only two did, and this is because there apparently was no config on their interfaces at all! This was all that was there for those two:

interface GigabitEthernet1/0/6

swicthport mode access vlan 200

So, is the problem that the voice traffic is on vlan 1? What's the best way to solve this issue?

[Jerome BERTHIER]

Hi


Using vlan 1 is a bad idea because it is the default one so it is everywhere in your switch.


A port with voice vlan defined is acting in a kind of trunk.

Voice vlan is announced to the phone using cdp (or lldp if needed). Then this device will tag its traffic using this value.

But my guess is that using voice vlan 1 is confusing the switch.


Changing the value of voice vlan might be difficult but it should be the next step.


For now, you might try to move the port in trunk mode and choose vlan 200 as native :

interface GigabitEthernet1/0/5

 switchport trunk native vlan 200
 switchport trunk allowed vlan 1,200
 switchport mode trunk

switchport voice vlan 1


I'm sure it will work but you might try it.

If it works then move voice traffic on another vlan and you can fall back to the first setup :

interface GigabitEthernet1/0/5
switchport mode access vlan 200
switchport voice vlan <new_number>


Regards


Jérôme

[paul driver]

Hello

---

@andrewohanian wrote:

 When I added "switchport access vlan 200" the devices did not get new IPs.

If you change the acces port to another vlan users won’t be able to receive dhcp addressing if you dhcp server doesn’t know how to reach vlan 200 - 

anything other than vlan 1 is by default tagged traffic so if your dhcp server resides on vlan 1 (untagged) and your users are in vlan 200 (tagged)

Then unless you have a trunk interconnecting  the dhcp server and this  switch that can carry tagged traffic it won’t work

do you have a L3 address for vlan 200?

[andrewohanian]

Yes, as stated two devices actually did receive IPs. These devices had no config at all on their interface. After my change all they had was "switchport access vlan 200"

[andresfr]

Hello Andrew,

I hope you're doing great.

Quick question, will you be using Cisco IP Phones or third party IP Phones?

If using Cisco IP Phones, the suggested configuration will be the following:

configure terminal

 interface GigabitEthernetX/Y/Z
  switchport mode access vlan <data_VLAN_ID>
  switchport voice vlan <voice_VLAN_ID>

  end

!

If using third party IP Phones, I would suggest the same previous configuration, but additionally you can enable LLDP globally to see if the IP Phones can get the information about the Voice VLAN dinamically:

configure terminal

 lldp run

 end

!

One additional consideration regarding the obtention of IP addresses via DHCP, and as it has already been commented, is that you need to have a DHCP relay (ip helper address) configured in the layer 3 VLAN interface for both the Data VLAN and the Voice VLAN if the DHCP Server resides on a different subnet. If you have those VLAN SVIs on this same switch, the you can add the ip helper on those. If the layer 3 device performing the inter-VLAN routing is a different one, you need to have a trunk link to that device and configure the DHCP relay on that other device.

interface vlan A

 ip address w1.x1.y1.z1

 ip helper-address <DHCP_Server_IP_address>

 exit

!

interface vlan B

 ip address w2.x2.y2.z2

 ip helper-address <DHCP_Server_IP_address>

 exit

end

!

I hope you find this information useful.

Regards,

[andrewohanian]

Thank you, yes there is an SVI with the helper address. User ports that only have "switchport access vlan 200" and nothing else are able to get an IP.

But, the user ports with

switchport access vlan 200

switchport voice vlan 1

Could not. That's the issue I'm wondering about - is it due to the native vlan use for voice?

[andresfr]

Hello Andrew,

1. Just to clarify, when you say that users port that only have "switchport access vlan 200" and nothing else are able to get an IP address, to what devices are you referring to? IP Phones or PCs.

2. Those devices that are getting IP addresses,  are getting IP addresses corresponding to VLAN 200 subnet for which you have a DHCP pool in the DHCP server, correct?

3. Are you having a different/additional DHCP pool for the subnet that corresponds to VLAN 1?

4. Are you having the IP helper address in VLAN 1 SVI as well?

5. Can you confirm that we are talking about Cisco IP Phones?

Depending on the end devices that you're connecting to the access ports configured with both the 'swithcport access vlan 200' and the 'switchport voice vlan 1' commands, if those are Cisco IP Phones they will learn via CDP that the voice VLAN is VLAN 1. If you're not having a DHCP scope for the subnet defined for VLAN 1, and/or if you are not having the ip-helper address in the VLAN 1 SVI, then those IP Phones will not be able to obtain and IP address with that configuration.

However, a PC connected to any of the interfaces configured with both the Data VLAN and the Voice VLAN with the commands already commented, should be able to still get an IP address in VLAN 200. Can you confirm this?

Regards,

[pieterh]

switchport voice vlan <x> is a means for (cisco) phones to negotiate the voice vlan with the switch (using CDP or LLDP)

it should be configured ONLY on access ports not on vlan trunking ports!

the cisco phone has an internal switch that separates the voice vlan for internal use and a "passthrough" port for a connected device lik a PC, this will use the access-vlan configured on the port

so two devices can use the same switchport on different vlans while the port is still an access port.

when both voice vlan and acess vlan are the same (vlan1) i'm not sure how this behaves.

but if you create a new vlan200 and connect both phone and pc to the same switchport it should show

     switchport mode access

     switchport voice vlan 1

     switchport access vlan 200

[pieterh]

apart from above you still need DHCP server configured for both vlans and routing properly setup