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Issue with voice vlan determination



I have a Cisco SG300-10PP switch.  It has become convinced that the voice VLAN should be 64 and I cannot disabuse it of that notion.  I have reset it to factory defaults and it still thinks this.  I have manually set the voice VLAN ID to 68, which is what I want it to be.  The upstream switch is telling it 68 via CDP, but the SG300 still thinks that the agreed upon VLAN is 64.  I deleted the VLAN off the switch, but as soon as I connect a phone, it recreates the VLAN.  I am not sure how to fix this issue.  The switch is running version  I tried setting the port to trunk mode as one of the posts suggested but that did not seem to help.  When I edit the Smartport Type settings for ip_phone or ip_phone_desktop, the voice VLAN number is not changeable.

I would appreciate any help on how to get this working the way that it should.



4 Replies 4

Yiu Kay Lee
Cisco Employee
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Yiu Kay Lee


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Do I need Smartnet or a support contract to open a case on this issue?  It is a brand new switch but I do not have any extra support on it.



Mr. bfflusek,

I am sorry you are experiencing this issue.  The issue is if you are using the Auto Voice VLAN (AVV).  The AVV uses a protocol called VSDP and the switch will learn about the Voice VLAN.  

VSDP is a Cisco defined protocol for voice service discovery.

VSDP is tied in with the Auto Voice VLAN (AVV).  Instead of using AVV try using the Telephony OUI mode instead.

Here is the descriptions in regards to the two feature from the Admin Guide:

Here is the SG300 admin guide:

The SG300 pretty much says the same thing but posted below is from the SG500 admin guide as I believe it is a cleaner explanation.

Auto Voice VLAN

In Auto Voice VLAN mode, the voice VLAN can be either the default voice VLAN, manually configured, or learned from external devices such as UC3xx/5xx and from switches that advertise voice VLAN in CDP or VSDP. VSDP is a Cisco defined protocol for voice service discovery. Unlike Telephony OUI mode that detects voice devices based on telephony OUI, Auto Voice VLAN mode depends on Auto Smartport to dynamically add the ports to the voice VLAN. Auto Smartport, if enabled, adds a port to the voice VLAN if it detects an attaching device to the port that advertises itself as a phone or media end points through CDP and/or LLDP-MED.

Telephony OUI

In Telephony OUI mode, the voice VLAN must be a manually-configured VLAN, and cannot be the default VLAN. When the device is in Telephony OUI mode and a port is manually configured as a candidate to join the voice VLAN, the device dynamically adds the port to the voice VLAN if it receives a packet with a source MAC address matching to one of the configured telephony OUIs. An OUI is the first three bytes of an Ethernet MAC address. For more information about Telephony OUI, see Configuring Telephony OUI.

Using Telephone OUT this should allow the functions of CDP to work independently from the Voice VLAN and not change your Voice VLAN configuration.

Hope this helps,


Michael D.

If this post is helpful please rate or mark as correct.

Hi Yiu Kay Lee,

Please refrain putting comments on the Cisco Support Community bringing users away from the site.

If you can provide any assistance to this user's issue, please post the comment directly to this discussion.

Thank you.

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