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Cat4000 GEtherchannel - DUP Packets

I have some odd trouble with GEtherchannels

The setup is like this:


C4006-c4003 is a 2port trunked GEC. Traffic of Hosts that are connected to those switches is fine.

C4003-Juniper(m320) is a 2port trunked GEC, too. Now, Traffic between the juniper and *some* hosts connected to the C4006 gets mulitiplicated randomly, reproducable, but not determinable. Its reproducable with ping, which then tells "DUP!".

Everytime the Channel is touched, the set of hosts on the C4006 which show the phenomen changes.

Disabling the Channel C4003-Juniper makes that problem disappear.


Re: Cat4000 GEtherchannel - DUP Packets

There is a possibility that you are having a unidirectional link here. Kindly enbale UDLD in aggressive mode in the cisco device and check whether the port is going in err-disable mode. If it's going in err-disable mode then there is a unidirectional link in your topology.

Do a no shut to bring the disabled port up after the problem is corrected.

Community Member

Re: Cat4000 GEtherchannel - DUP Packets


Thank you for your Input.

I have tested UDLD on the C4003-C4006 Channel and this runs smooth, i.e. both Ports do have a bidi Link.

4003-Juniper i cannot test UDLD, since Juniper does not speak UDLD. On the other Hand, both Ports of that Channel individually -and not configured as Channel- run fine, too.

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