Switch ports did an up/down sequence after being placed in etherchannel with no cables connected, wierd.

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Feb 10th, 2010
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Hi Everyone


I created an etherchannel on two ports (2960 switch) and placed them into an etherchannel.  Did the same on the other switch Cisco 3020 blade chassis switch.  Without connecting any cables the 2960 had done an up/down sequence as though a cable had been connected and yet this had not been done.  Can someone try and help with what could be the technical explanation of this interesting phenomena.  the etherchannel was a trunk and the ports were sitting in vlan 200 and this vlan was also configured as the native vlan for the trunk.


Please,  please help - any comment is appreciated.


Sydney

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Ganesh Hariharan Sat, 02/13/2010 - 00:09
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Hi Everyone


I created an etherchannel on two ports (2960 switch) and placed them into an etherchannel.  Did the same on the other switch Cisco 3020 blade chassis switch.  Without connecting any cables the 2960 had done an up/down sequence as though a cable had been connected and yet this had not been done.  Can someone try and help with what could be the technical explanation of this interesting phenomena.  the etherchannel was a trunk and the ports were sitting in vlan 200 and this vlan was also configured as the native vlan for the trunk.


Please,  please help - any comment is appreciated.


Sydney


Hi Sydney,


It can be possible that speed and duplex setting between the switches are not in sync. Configure all interfaces in an EtherChannel to operate at the same speeds and duplex modes.Enable all interfaces in an EtherChannel. If you shut down an interface in an EtherChannel, it is treated as a link failure, and its traffic is transferred to one of the remaining interfaces in the EtherChannel.


For EtherChannels:


–Assign all interfaces in the EtherChannel to the same VLAN, or configure them as trunks.

–If you configure an EtherChannel from trunk interfaces, verify that the trunking mode (802.1Q) is the same on all the trunks. Inconsistent trunk modes on EtherChannel interfaces can have unexpected results.

–An EtherChannel supports the same allowed range of VLANs on all the interfaces in a trunking Layer 2


Hope to help


If helpful do rate the post


Ganesh.H

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