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Issue with Four Cisco 7940 phones connected to Cisco Swtich 3550 not lighting up.

Chandra sekhar
Level 1
Level 1


Need help on Cisco phones power up. This is for my Home Lab. 

I have purchased Cisco 3550 Switch and 4 Cisco 7940 phones, when i try connecting the phones to switch, nothing happens (Blank Screen).

On the Switch side, i see a behavior where the respective ports blink for 2 to 3 sec (bright red) and go into "error disabled state".

I have configured the vlan interface, spanning tree portfast etc...

Issue could not be with switch as i could successfully connect my Cisco 2811 router to it and ping.

I was in assumption that Cisco phones would power up automatically when connected to switch, at least the lights on them until configuration is finished.

BTW, these Cisco phones are refurbished, tested and came with 1 year warranty

Please advise.

Thanks in advance.

7 Replies 7

Leo Laohoo
Hall of Fame
Hall of Fame

On the Switch side, i see a behavior where the respective ports blink for 2 to 3 sec (bright red) and go into "error disabled state".

Post the complete output to the command "sh interface status err".

Sorry for the late response. I was out of town for few days.

s1#show interface status err-disabled

Port Name Status Reason Err-disabled Vlans
Fa0/23 err-disabled link-flap

*Mar 1 00:40:55.607: %PM-4-ERR_DISABLE: link-flap error detected on Fa0/23, putting Fa0/23 in err-disable state

s1#show errdisable recovery
ErrDisable Reason Timer Status
----------------- --------------
arp-inspection Disabled
bpduguard Disabled
channel-misconfig Disabled
dhcp-rate-limit Disabled
dtp-flap Disabled
gbic-invalid Disabled
l2ptguard Disabled
link-flap Enabled
mac-limit Disabled
link-monitor-failure Disabled
loopback Disabled
oam-remote-failure Disabled
pagp-flap Disabled
port-mode-failure Disabled
psecure-violation Disabled
security-violation Disabled
sfp-config-mismatch Disabled
storm-control Disabled
udld Disabled
unicast-flood Disabled
vmps Disabled

this is for my lab, it's a New refurbished switch.

i am using port fast Ethernet 2/23 for test, I have also attached my switch configuration.

interface FastEthernet0/23
switchport access vlan 11
switchport trunk encapsulation dot1q
switchport mode trunk
switchport voice vlan dot1p
switchport priority extend trust
mls qos trust cos
priority-queue out
spanning-tree portfast
spanning-tree bpduguard enable

 I have seen some references about the cable been wrong, so i have tested the cables in a different environment and they work fine.

s1#show inter fastEthernet 0/23
FastEthernet0/23 is down, line protocol is down (err-disabled)
Hardware is Fast Ethernet, address is 000c.316b.5897 (bia 000c.316b.5897)
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Auto-duplex, 100Mb/s, media type is 10/100BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:10, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
1 packets input, 64 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
113 packets output, 7232 bytes, 0 underruns
0 output errors, 0 collisions, 15 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
0 output buffer failures, 0 output buffers swapped out

I have done some more research on it.

My Switch type 

s1#show ver
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(50)SE1, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Mon 06-Apr-09 08:51 by amvarma
Image text-base: 0x00003000, data-base: 0x013EEB64

ROM: Bootstrap program is C3550 boot loader

s1 uptime is 2 hours, 34 minutes
System returned to ROM by power-on
System image file is "flash:/c3550-ipservicesk9-mz.122-50.SE1.bin"

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

If you require further assistance please contact us by sending email to

Cisco WS-C3550-24 (PowerPC) processor (revision H0) with 65526K/8192K bytes of memory.

s1#show power inline
Interface Admin Oper Power Device Class Max
--------- ------ ---------- ------- ------------------- ----- ----

s1#show power inline fastEthernet 0/23
Interface Fa0/23: inline power not supported

looking at the above output, looks like my switch doesn't support POE and Inline power 

could someone please confirm ?

could someone please confirm ?

Please post the complete output to the command "sh version". 

Get the exact model of your switch, and see here



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