Trunking Configuration Problem - ErrDisable

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Nov 9th, 2007
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Hi Experts,

I encountered one problem as below..


ERR_DISABLE: channel-misconfig error detected on Po1, putting Fa0/23 in err-disable state


When I tried to configure etherchannel group for 2 fastethernet port of fa0/23 and fa0/24.


Fa0/23 is connected to Core Switch 1.

Fa0/24 is connected to Core Switch 2.

Both are one channel-group 1 mode on.


Config as below:


On Core Switch 1:

Int fa2/5

Description To Dist Sw__1_Fa0/23

Switchport trunk encapsulation dot1q

switchport mode trunk

speed 100

duplex full


On Core Switch 2:

Description To Dist Sw_1_Fa0/24

Int fa2/5

Switchport trunk encapsulation dot1q

switchport mode trunk

speed 100

duples full


On Dist SW_1,


Interface Port-Channel 1

Switchport trunk encapsulation dot1q

Switchport mode trunk

...

...

...

Int fa0/23

switchport trunk encapsulation dot1q

switchport mode trunk

speed 100

duplex full

channel-group 1 mode on

...

...

...

Int fa0/24

switchport trunk encapsulation dot1q

switchport mode trunk

speed 100

duplex full

channel-group 1 mode on

...

...

...


Note: When I leave one cross cable not connected, it doesn';t give any problem.

Only when I connect both cross cable to core Switch 1 and 2, then it will go to Err-Disable mode for the port fa0/23 and fa0/24.


Thanks in advanced.



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Edison Ortiz Fri, 11/09/2007 - 08:31
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To avoid this err-disable message, you need to shutdown both switchports at each link-partner before entering channel-group x mode x


Once you are done with the channel-group configuration, you can issue a 'no shut' under the interfaces.

Kevin Dorrell Fri, 11/09/2007 - 08:34
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Etherchannel bundles must always go between the same two switches. You cannot have one link of a bundle going to one switch, and another to a different switch.


Furthermore, the two links would need to be bundled at the core switch end as well.


Kevin Dorrell

Luxembourg


cindylee27 Fri, 11/09/2007 - 08:52
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Guys,

Thanks for your reply.


Edison, Did u mean that I need to do a shut on interface fa0/23 and fa0/24,before applying the command : "channel-group 1 mode on" to prevent this problem?

Can I say that once applied the command above, I can do a "no shut" and will solve the problem?


Kevin, If that is the case, How can I configure 2 redundancy links to both Core Swithes,in case Core Switch 1 or 2 fails.. ?


Thanks again..




Edison Ortiz Fri, 11/09/2007 - 09:03
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I missed the part of the destination device being different.


As Kevin pointed out, you can't have 2 sources switchports going to 2 different destination devices in an etherchannel.

cindylee27 Fri, 11/09/2007 - 10:37
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So,how can I create 2 connections to 2 diff Core Sw which both are trunked to each other ? CS1 -> CS2 (etherchannel trunk ).


Will I cause a looping and how to configure redundancy for this type of connection/??


Thanks.


Edison Ortiz Fri, 11/09/2007 - 11:05
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Trunk is allowed on both connections while etherchanneling is not, there are 2 different features.


Etherchannel provides bandwidth aggregation while trunking provides the ability to send multiple Vlans over a single link.


You don't need to etherchannel in order to get redundancy. Just configure the trunking and plug the links from the leaf switch up to the Cores.

cindylee27 Fri, 11/09/2007 - 11:17
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Thanks Edison..

I read somewhere there looping problem might happens if this is the case..Can I say that the looping is being taken care off by STP automatically or is there any configurations that you can point me to ?


Is that means tat I can configure without port-channel 1 for the fastethernet 0/23 and 0/24 ?


and connect both to Core Switch 1 and 2 respectively?


Thanks again.




Edison Ortiz Fri, 11/09/2007 - 12:09
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The looping is prevented with STP. Depending on how your STP is configured, one of those ports will be blocked.


For instance, if Core 1 is the STP Root for all Vlans, and port 0/23 is connected to this Core - will be set to FWD mode while 0/24 will be set to BLK mode (you can verify this with show spanning-tree command on the leaf switch).


If you have multiple Vlans, you can load-balance them by assigning Core1 STP Root half of the Vlans while Core2 STP Root for the other half.

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