I have a Cisco 3550. I wanted to connect a 9971(used) to it, but it is not going beyond POST. I see the keys blinking but nothing happens after that, and this happens in a loop. Could that be a problem with Phone or with Switch?

Switch Information - C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6

Model number: WS-C3550-24PWR-SMI

  • Do you have the DHCP server sending the correct options to point to the server with the phone configuration?
    – Ron Maupin
    Feb 6, 2017 at 17:30
  • Yes, DHCP Server is there. Infact other phones(7960) connected to the same switch are working fine. On 9971 I don't even see the Cisco Logo. POST is in loop.
    – MUSR
    Feb 6, 2017 at 17:32
  • You may have a hardware problem. There isn't much we can do about that.
    – Ron Maupin
    Feb 6, 2017 at 17:33
  • Are you sure you've got the right firmware on the TFTP server for it? If you're doing CME or an older CCM it may not have the right code.
    – rnxrx
    Feb 6, 2017 at 18:12

1 Answer 1


Probably an inline power issue.

Phone Specs says

IEEE Power over Ethernet 802.3af and 802.3at supported, class 4. The 9971 is compatible with both class 3 and class 4 IEEE PoE switch blades and supports both Cisco Discovery Protocol (CDP) and Link Layer Discovery Protocol - Power over Ethernet (LLDP-PoE)

Switch Spec says

Additionally, up to 15.4W/port of inline power on every 10/100 port ensures maximum device support for IP telephony and wireless LAN deployments.

Maximum power availability for a converged voice and data network is attainable when the Catalyst 3550-24 PWR switch is combined with the Cisco Redundant Power System 675 (RPS 675) (available 1HCY03) for seamless protection against internal power supply failures and an uninterruptible power supply (UPS) system to safeguard against power outages.


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