Troubleshooting VLANs & Trunks

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8

Hi Jason,

This message shows up when your switch receives a frame with the same source MAC address on two different interfaces.

Do you see this for one MAC address or multiple? If you see multiple MAC address, you might have a L2 loop. If you only see one source MAC address, it’s probably a misconfiguration. Track it down like this:

SW1#show mac address-table dynamic address 0017.94a5.a618 
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
 200    0017.94a5.a618    DYNAMIC     Gi0/34
Total Mac Addresses for this criterion: 1

If you have multiple switches, do this on all switches until you get to the source. One example where this can happen is when you configure link aggregation / load balancing on a server but not on your switch.

Rene

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