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New Member

%PM-4-ERR_DISABLE: loopback error detected

ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/23.

%PM-4-ERR_DISABLE: loopback error detected on Fa0/23, putting Fa0/23 in err-disable state

Information:

1. swith 3550(f0/23,trunk,up-SW) link to 3550(f0/23,trunk,down-sw)

2. disable port is not used.

3. port used(connect to cisco router,cisco switch,IPS,log server,ibm router,sniffer)

4. IOS (C3550-I9Q3L2-M), Version 12.1(14)EA1a

How to check where 's loopback port problem?

5 REPLIES
New Member

Re: %PM-4-ERR_DISABLE: loopback error detected

up-SW

interface FastEthernet0/23

switchport trunk encapsulation dot1q

switchport mode trunk

no cdp enable

down-SW

interface FastEthernet0/23

switchport trunk encapsulation dot1q

switchport mode trunk

no cdp enable

Re: %PM-4-ERR_DISABLE: loopback error detected

Hi

The possible reason for this loopback error is coz of bad cable which is connected on the ports.

have you tried changing the cable and checked for the error ? if not can you try it off and check ...

regds

Re: %PM-4-ERR_DISABLE: loopback error detected

Hello,

check if changing the cable(s) makes a difference, also, do you see any STP messages in any of the switch logs ?

Regards,

GNT

Re: %PM-4-ERR_DISABLE: loopback error detected

Hi Friend,

Also if changing the cable did not resolve the issue then there may be a STP loop in you network.

The problem occurs because the keepalive packet is looped back to the port that sent the keepalive. Keepalives are sent on the Catalyst switches in order to prevent loops in the network. Keepalives are enabled by default on all interfaces. You see this problem on the device that detects and breaks the loop, but not on the device that causes the loop.

Workaround will be to issue the "no keepalive" interface command in order to disable keepalives. A disablement of the keepalive prevents errdisablement of the interface, but it does not remove the loop.

To remove the loop you may have to trace the cables and switches and find out that out.

Regards,

Ankur

New Member

Re: %PM-4-ERR_DISABLE: loopback error detected

thanks everybody,now input command "no keepalive" interface and can to resolved error but now i try to find port or cable or ..?.. for problem occures.

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