Information Technology Reference
In-Depth Information
Here's the process you should use for troubleshooting network-related issues:
Issue 1: Verifying PoE
Obviously, if the IP phone does not receive power, nothing is going to work correctly. You
can quickly diagnose this issue by asking the user if her phone is displaying anything on
the screen. If not, here are your areas of focus:
Check the physical connections:
Verify that the IP phone is securely plugged in,
verify all patch panel connections, and verify the Ethernet cable used has all eight
pins functioning properly (because PoE uses the four pins not used by data).
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Check the PoE switch:
Ensure that the switch is online and operational, verify that
the PoE clients have not exhausted the switch power supply by using the show power
inline command, and use a show run command to verify that the port does not have
the command power inline never (which disables PoE).
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Check the IP phone:
Verify that the IP phone does not have expansion modules
causing it to exceed PoE capabilities, move the IP phone to a different port to see if it
receives power, try a different IP phone on the same port to see if it receives power,
and be sure that the IP phone and PoE switch support a compatible PoE standard
(Cisco inline power, 802.3af, and 802.3at).
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Tip:
Before you move too far into the troubleshooting process, it's always best to reset
the phone's configuration settings to factory default. Although the various IP Phone mod-
els have different locations to reset the configuration, all of them will have the option.
Often, a bogus configuration item will end up stuck in one of the key fields that you may
not initially see. Resetting the phone configuration gives you a clean starting ground to
work from.
Issue 2: Voice VLAN Assignment
If an IP phone is assigned to the wrong VLAN, it may not be able to contact the necessary
supporting servers (DHCP, TFTP, CME, and so on). You can diagnose this and the follow-
ing issues when you receive a report that the IP phone is continually rebooting:
Check the switch configuration:
Ensure that you correctly configured the voice
VLAN by viewing the running-configuration (show run), verifying the interface oper-
ating mode by entering a show interface <interface_name> switchport command, ver-
ifying you created the voice VLAN on the switch (show vlan), verifying that the voice
VLAN is added to all applicable trunk connections (show interface trunk), and verify-
ing CDP is enabled on the port connected to the IP phone (because the voice VLAN
is sent to the IP phone using CDP).
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Check the IP phone:
If you have physical access to the IP phone, navigate to the
network settings page (using the Settings button on the phone). Verify that the IP
phone has received the voice VLAN configuration, verify the IP phone has an IP ad-
dress, and access the phone IP address in a web browser and view the log files for
more clues.
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