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New Member

ERR_DISABLE-Cisco 3550 Switch

Dear all

Please look at this below logs from cisco 3550 switch. pls guide me .

errdisable mode is detected here because of the loopback. pls anybody explain me what is this......

Jun 5 13:36:20.502 IST: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/3.

Jun 5 13:36:20.502 IST: %PM-4-ERR_DISABLE: loopback error detected on Fa0/3, putting Fa0/3 in err-disable state


Re: ERR_DISABLE-Cisco 3550 Switch

Hi Rajesh,

Have a look at this

Explanation This message means that a loopback condition might be the result of a balun cable incorrectly connected into a port. On PoE switches, this message might appear when a device that can be powered by either a PoE switch port or by AC power is not being powered by an external AC power source and is connected to a port that has been configured with the power inline never interface configuration command. [chars] is the port.

Recommended Action On non-PoE switches, check the cables. If a balun cable is connected and the loopback condition is desired, no action is required. Otherwise, connect the correct cable, and then enable the port up by entering the no shutdown interface configuration command. On PoE switches, remove the device or configure the port by entering the power inline auto, the shutdown, and the no shutdown interface configuration commands.

Also you can overcome errdisable condition configuring errdisable recovery procedure

HTH, if yes please rate the post.


New Member

Re: ERR_DISABLE-Cisco 3550 Switch

Hi Ankur

The mentioned 3550 switch is not having the PoE ports.

The port no fa 0/3 is connected to the L2 switch ( brand: HUAWUI) And one more thing i want to what is balun cable. presently we connected these two switches with ethernet cable.

After getting this error, if i give shut and no shut then this port comming up. but after some time later the error comming. let me know " the errdisable cause is loopback" why and how loopback. is it any looping kind of thing happening. for your information no other redudent links are there in between these switches.

Re: ERR_DISABLE-Cisco 3550 Switch

Hi Rajesh,

I have seen this behavior many a times on these switches and there are some bugs also for the same and the workaround is to disable "keepalives" on that interface with "no keepalives" command.

Can you please update which IOS code you are running on your switch?



New Member

Re: ERR_DISABLE-Cisco 3550 Switch

Hi ankur

pls look at the below show version output.

Cisco Internetwork Operating System Software

IOS (tm) C3550 Software (C3550-I9Q3L2-M), Version 12.1(22)EA3, RELEASE SOFTWARE


Copyright (c) 1986-2005 by cisco Systems, Inc.

Compiled Tue 25-Jan-05 20:17 by antonino

Image text-base: 0x00003000, data-base: 0x006CB894

ROM: Bootstrap program is C3550 boot loader

BANGCAS4 uptime is 15 weeks, 6 days, 15 hours, 38 minutes

System returned to ROM by power-on

System restarted at 20:50:24 IST Thu Feb 16 2006

System image file is "flash:c3550-i9q3l2-mz.121-22.EA3/c3550-i9q3l2-mz.121-22.EA


cisco WS-C3550-24-DC-SMI (PowerPC) processor (revision P0) with 65526K/8192K byt

es of memory.

are u meant to ubgrade to some other IOS.

Re: ERR_DISABLE-Cisco 3550 Switch

Hi Rajesh,

Have you tried disabling the keepalives on this interface? Disabling keepalives should resolve this issue which are looped back to the interface from where there are sent.

There are few bugs reported for this issue where disabling keepalives is the workaround for this problem. You may contact TAC for futher details on the same.



New Member

Re: ERR_DISABLE-Cisco 3550 Switch

i disabled the keepalives. Presently no problem. thanks ankur.

New Member

Re: ERR_DISABLE-Cisco 3550 Switch

Is there any interesting document about the keepalive protocol on cisco switches (and how it really work) ?

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