etherchannel configuration issue (edit)

Unanswered Question
Feb 3rd, 2010

Hello experts,

I attached last time the config and error with this message. But don't know why it didn't attach. anyway i attach those files now.

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


I have this problem too.
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Giuseppe Larosa Wed, 02/03/2010 - 13:33

Duplicated thread

let's go on on the other one where Reza has answered

Hope to help


Giuseppe Larosa Thu, 02/04/2010 - 15:19

Hello Saimun,

on one side you have used channel-mode on => build a bundle unconditionally

on the other device you have used channel-mode active =  use LACP protocol to build a bundle this side actively tries to negotiate

configuration must match on this aspect.

in addition to  this MAC addresses are flapping between two bundles.

Fix the channel mode first, then if error messages still appear you need to talk with server people they may  have bundled on server side in a different way (a single bundle instead of two)

Hope to help


saimunpial Fri, 02/05/2010 - 05:01

Hello Giuslar,

yes i find that mistake yesterday too. i recorrect it. but after that even that vlan flapping was going on. I create one instead of two port channel and apply lacp port priority. so out of 16 ports always 8 are up and rest for the hot redundancy. anyway thanks for the tips.


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