protocal application invalid

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Sep 7th, 2006
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Now, my 7940 start up, and phone only "configuration vlan" "configuration IP" and then display "protocal application invalid", it seems like died.I want to configure manually, but Setting menu don't work.

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Rob Huffman Fri, 09/08/2006 - 05:20
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Hi Kannis,

Her is an excerpt from a Cisco document that seems to address this problem:


The 7960 IP phone fails to perform the boot process correctly. As the phone boots, this error message displays in the phone LCD:

Protocol Application Invalid


When you examine the sniffer trace between the DHCP server and the phone, you can identify that the phone accepts a DHCP offer from the data VLAN (the native VLAN) instead of the voice VLAN. The phone tries to communicate with the voice VLAN with the IP address that belongs to the data VLAN.

This problem can happen under these conditions:

With an IP Phone 7940/7960 with firmware version 7.2(2) and earlier

When a DHCP server sends a response packet in an untagged format

With a DHCP server switch port that is configured with voice VLAN or with a trunk that contains that voice VLAN

When option 150 is not set for the native VLAN on the DHCP server

When Cisco Discovery Protocol (CDP) on the switch and the phone do not converge in a timely fashion


The workaround for this problem is to complete these steps:

Configure option 150 in the native VLAN scope on the DHCP server.

Complete these steps:

Choose Start > Programs > Administrative Tools > DHCP.

Right-click the DHCP server and choose Set Predefined Options in the pop-up window.

Click Add.

Enter TFTP Server IP Address in the Name field.

Choose IP Address from the Data type menu.

Enter 150 in the Code field

Click OK.

Choose 150 TFTP Server IP Address from the Option name menu.

Enter the IP address of the TFTP server in the IP Address field, which is in the Value area.

Click OK.


Remove the voice VLAN command from the phone switch port and leave the switch port as an access port on the native VLAN.

For example, if the phone is connected to a Catalyst 3550 multilayer switch, remove this line:

switchport voice vlan 205

Reboot the 7940/7960 IP phone.

The phone upgrades its load with the use of an IP address on the native VLAN.

Add the voice vlan command back to the switch port.

Reboot the 7940/7960 IP phone.

The phone now comes up with an IP address on the voice VLAN.

Here is a link to the actual doc:

Please let us know if this 7940 was ever converted from Skinny to SIP??

Hope this helps!


Please remember to rate helpful posts.....

dany.datacraft Sun, 12/21/2008 - 23:03
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I had similar problem in one of our customer this morning. However, the problem only applies to all new phones. Existing phones are able to register to the CCM.

Last changes done on the network:

1. Upgraded CCM from 4.2 to 6.1

2. Changed DHCP server from Cisco Router to QOIP (software based).

After some troubleshooting, we found out that the DHCP server is using option 66 instead of option 150. Option 66 is configured as the TFTP server IP address.

Subsequently we found out that the phone sends out DNS request for the TFTP server IP address, which was rejected by the DNS server. We resolved the problem by changing option 66 to hostname instead of IP address.

Hope it helps...


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