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Bekzod Fakhriddinov

Cisco switch is not detecting ip phone

Hello guys,

 we have 3 cisco sbc 350 -48-fp-4x and connecting ip phones and pc to them via single port. The problem we have - ip phones are not detected on the random ports of all 3 switches  : switch1- 19 ports  , sw2 - 12 ports , sw3 - 42 ports not detected . Port shows down, but if user takes the same phone with the same  patchcord and connect to working port phones comes up and registers. 

Any advice guys ? 

Thank you 

VIP Guru

we need more information  - all these 3 switches are stacked ?


post complete output as below :


show run from all switches ?


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Giuseppe Larosa
Hall of Fame Master

Hello @Bekzod Fakhriddinov ,

unless you are using power injectors or external power your IP phones are relying on PoE Power over Ethernet are SW2 and Sw3 capable of providing PoE on their ports ?


Hope to help




Are the configurations different on these ports where they are working vs not?  Did you run out of available PoE on the switches, i.e. using several high PoE consuming devices (switch can support full power on all ports, just not at the same time...)?  Is the end to end cabling good - quick test is taking a phone directly to the switch and seeing if it works while bypassing the building cabling?  Are runs too long and/or poor cabling not following TIA/568 cabling (color code definitely matters; more so when PoE is involved)?  Is cabling running through lossy old infrastructure, such as repurposed 66 or 110 TELCO blocks?  Was the building recently painted, and jacks have paint overspray?  Have you updated them to modern firmware and bootloader? Be careful, often a multi-patch process on these SMB switches.  I can think of a lot of reasons, but the top are: poor cabling, out of available PoE, or switch firmware.