GigabitEthernet interface down

Unanswered Question
May 8th, 2007

The GigabitEthernet interface down between 2 switches is down. This is part of a Ethernchannel bundle and it shows the following:

GigabitEthernetx/y is down, line protocol is down (err-disabled)

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, media type is SX

input flow-control is off, output flow-control is off

Clock mode is auto

But I cannot see anything in the 'show log' and nothing even came up in the logs for me to be able to tell when it went down. It was when i was doing a physical check that i saw that it was down. Logging is enabled.

There is no speed or duplex issue.

The inteface is configured thus:

interface GigabitEthernetx/y


switchport trunk encapsulation dot1q

switchport mode trunk

no ip address

udld port

rmon collection stats 160

channel-group 1 mode desirable


Please what can be the problem? Please help.


I have this problem too.
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ankbhasi Tue, 05/08/2007 - 23:20

Hi Friend,

Your interface is going into errdisable state which is making it go down.

GigabitEthernetx/y is down, line protocol is down (err-disabled) <<<<<<-----

So I believe it is some misconfiguration in etherchannel which is making it go into errdisable state.

Can you try "channel-group 1 mode on" on all the ports which are part of etherchannel and olso same thing on the remote switch ports which are connected to this switch etherchannel ports.



londint Tue, 05/08/2007 - 23:59


So please how will changing the channel-group 1 mode from 'desireable' to 'on' make a difference?

Also why did this never show up in the Show logging?


ankbhasi Wed, 05/09/2007 - 00:08

Hi Friend,

I believe this could be a etherchannel negotiation issue so I thaught to give a try with mode "ON" which will stop PAGP protocol on etherchannel links.

Also on the other hand you can enable "errdisable detect cause" which may report what is the cause of gig interface going into errdisable state.



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londint Wed, 05/09/2007 - 00:19

Thanks once again.

What will be the impact enabling this during production hours.?

It is on a Cat 6500.


ankbhasi Wed, 05/09/2007 - 00:27

Hi Friend,

Though changing channel group should not have much impact, may be less than seconds but I will recommned you to give it a try when you have minimum users.

Also if you planning to configure erridisable detect cause it will not have any affect.



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londint Wed, 05/09/2007 - 01:08

Thanks. I will do this after production hours and give you a feedback. Thanks


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