etherchannel configuration issue

Unanswered Question
Feb 3rd, 2010

Hello experts,

I have some confusion regarding etherchannel. The scenario is

1) one the IBM blade server there are 4 cisco 3110G switch in stack and the other side there are 6 3750G switches in stack.

2) every first 2 ports of the 3110G switch are connects to 5th 3750G  switch and other 2 ports of 3110G switches connect to 6 switch.

3) in total 8 ports of these four 3110G switches in port channel 5 and other 8 ports are in port channel 6.

4) the both port channels are in trunk mode and allowed 5 vlans and one of them as native vlan.

the problem arise after configure the port-channel 6 the whole network goes down. So I shut down the port channel 6. Now the port-channel 5 is working again and the rest of the network. the error log i am sending with attachment as well as the config. My question is

1) whether there is a loop for this native vlan. because it exist in the both port channel and i have seen that native vlan is flapping between those two port channels.

2) is it possible to configure the spanning tree for these two port channels and assign cost. Because these two port channels are working as trunk. As far as I understand even the port channels are in trunking mode spanning tree will consider each port channel as a single link instead of trunk.

I would appreciate for your assist.

Saimun Pial

Network Engineer


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Reza Sharifi Wed, 02/03/2010 - 07:10

Hello Saimun,

You did not attached the files.

Also did you configure the native VLAN on both sides (3110G and 3750)?

The native VLAN number has to be the same on both switches.



saimunpial Thu, 02/04/2010 - 02:02

hello reza,

thanks a lot for your quick answer. i edit my last message and send the both side config files as well as the error log. But i am sorry that i edit the second one. so you can have a look at "etherchannel configuration issue (edit)".

the second answer is yes. i have given the native vlan on both side. anyway may be you will find something else as well in the configuration. I shut down the 2nd port channel. otherwise it generates the error log and i think it creates loop as well.


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