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Platform: - Cisco catalyst switches
Keywords: - Mac address flapping on switch, ether channel mis-configuration
Author: - Dinesh Aggarwal

The Problem: - We installed a new switch and made an ether channel of its two ports with another layer 3 switch. Ether channel was up but continuously messages were coming that mac address flapping.

The solution:- The problem was that on the new switch ether channel was in on mode while on layer 3 switch it was auto mode so ether channel  was not formed although on new switch in sh etherchannel summary command link was showing up up.

In actual the layer 3 switcvh did not formed the etherchannel so there was a loop in the network.

We made the ports on layer 3 switch also into on mode and everything started working fine.

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