This document describes one reason that Cisco IP Phone models 7940 and
7960 fail to boot with the error message Protocol Application
Invalid. This message displays in the liquid crystal display
(LCD). This document provides a workaround in the Cisco CallManager
Note: The problem that this document describes occurs in the IP Phone
7940/7960 with firmware versions 7.2(2) and earlier. For details, refer to
these Cisco bug IDs:
Cisco recommends that you have knowledge of these topics:
The information in this document is based on these software and
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Technical Tips Conventions for more information on document
The voice VLAN feature enables access ports to carry IP voice traffic
from an IP phone. The switch can connect to a 7940/7960 IP phone and carry IP
voice traffic. Because the sound quality of an IP phone call can deteriorate if
the data are unevenly sent, the switch supports QoS on the basis of IEEE 802.1P
class of service (CoS). QoS uses classification and scheduling in order to send
network traffic from the switch in a predictable manner. For more information
on QoS, refer to
QoS Solution Reference Network Design Guide. The 7940/7960 IP phone is a
configurable device, and you can configure it to forward traffic with an 802.1P
priority. You can configure the switch to trust or override the traffic
priority that an IP phone assigns. The 7940/7960 IP phone contains an
integrated three-port 10/100 switch, as Figure 1
shows. The ports provide dedicated connections to devices, as this list
Figure 1 – 7940/7960 IP Phone That Is Connected to a Switch
Port 1 connects to the switch or another VoIP
Port 2 is an internal 10/100 interface that carries the IP phone
Port 3 (access port) connects to a PC or another
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
When a DHCP server sends a response packet in an untagged
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
Configure option 150 in the native VLAN scope on the DHCP
Complete these steps:
Choose Start > Programs > Administrative Tools >
Right-click the DHCP server and choose Set Predefined
Options in the pop-up window.
The Option Type window displays, as Figure
Figure 2 – Option Type
Enter TFTP Server IP Address in the Name
See arrow A in Figure 2.
Choose IP Address from the Data type
See arrow B in Figure 2.
Enter 150 in the Code
See arrow C in Figure 2.
See arrow D in Figure 2.
The Predefined Options and Values window displays, as
Figure 3 shows:
Figure 3 – Predefined Options and
Choose 150 TFTP Server IP Address from the
Option name menu.
See arrow A in Figure 3.
Enter the IP address of the TFTP server in the IP Address field,
which is in the Value area.
See arrow B in Figure 3.
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
Arrow A identifies this line in Figure
Figure 4 – Catalyst 3550 Multilayer Switch VLAN Port
If the phone is connected to a Cisco Catalyst Express 500 series
switch, then change the smartport role of the port from IP Phone +
Desktop to Desktop. Refer to
Smartport Roles to Ports for configuring a Catalyst Express 500 switch
port with a particular smartport role.
Reboot the 7940/7960 IP phone.
The phone upgrades its load with the use of an IP address on the
Add the voice vlan command back to the switch
See arrow A in Figure 4.
Reboot the 7940/7960 IP phone.
The phone now comes up with an IP address on the voice VLAN.