EtherChannel MAC Flap Issue on a Cisco Switch - Solution!

Have you ever come across a following error message? *Mar  1 00:17:16.211: %SW_MATM-4-MACFLAP_NOTIF: Host 0015.2b57.8317 in vlan 1 is flapping between port Fa0/21 and port Fa0/23

The chances are you have, specially while configuring an EtherChannel. Here are some troubleshooting steps:

1) Make sure that the EtherChannel Port is UP via "show ip int brief" command or "show etherchannel summary"

2) sh mac address-table command will show you whether or not those ports belong to Po or Port-Channel interface

3) Here is how to resolve this issue:

  • Make sure that the "Channel-Protocol" is the same on both ends. PAgP or LACP or on. If one end is PAgP & the other is set to on EtherChannel won't form. Same goes with LACP.

  • Both sides of the EtherChannel have to have the same EtherChannel Negotiation Protocol i.e. PAgP or LACP. If you don't want to use Negotiation Protocol then both ends have to be set to "on".

  • The above-mentioned will resolve the issue.