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New Member

Cisco Cat 4500 +Cisco Phones


We have an issue where some user(s) have disconnected there phone (7941 phones) and then reconnected there phone to the same network cable (back to the way it was) ....and the phone has not come back on line - no power to the phone.

I can move the phone to another switch port  and all is ok but do you know what is causing this?

It is difficult to see exactly which port the phone came from so I can have a look at the interface status as there is around 400 phones connected to the back of the Cisco 4500 switch

I don't see any ports that are in an err-disabled state however I did notice there are some ports in an inactive state

Any thoughts?



VIP Super Bronze

Re: Cisco Cat 4500 +Cisco Phones

I have seen this type of behavior when you have reached the maximum PoE capabilities of the switch under it's current configuration. You should see syslog messages that power was denied. Also a "show power" command will show you the used vs. maximum available for Inline Power. If you are low it cannot supply power.

The best thing you can do is ensure it's running on 208v or higher feeds. The power capacity of the switch is limited when running on 120v or lower. The Cisco Power Calculator can help you see what capacity you have based on your hardware purchase.

Please remember to rate helpful responses and identify helpful or
New Member

Re: Cisco Cat 4500 +Cisco Phones


Thanks for your reply

below is a snippet from show power command

MERA0VOIP01#show power available
Power Summary                      Maximum
(in Watts)                    Used     Available
----------------------   ----       ---------
System Power (12V)        755         1360
Inline Power (-50V)          1050        1400
Backplane Power (3.3V)     40          40
----------------------                  ---          ---------
Total                                 1845        2800



MERA0VOIP01#sh power
Power                                             Fan      Inline
Supply    Model No             Type     Status       Sensor   Status
------  ----------------                              ---------  -----------  -------  -------
PS1     PWR-C45-2800AC    AC 2800W   good         good     good
PS2     PWR-C45-2800AC    AC 2800W   good         good     good

Power supplies needed by system    : 1
Power supplies currently available : 2

Power Summary                      Maximum
(in Watts)              Used           Available
----------------------   ----     ---------
System Power (12V)        755        1360
Inline Power (-50V)          1033       1400
Backplane Power (3.3V)     40          40
----------------------   ----     ---------
Total                               1828        2800

Hall of Fame Super Gold

Re: Cisco Cat 4500 +Cisco Phones

Have you tried running TDR on the line?

New Member

Re: Cisco Cat 4500 +Cisco Phones

Hi All,

This issue has been identified as a faulty module on the Cisco 4500 switch

- module swapped out and issue resolved