Today I will talk about Native VLAN Mismatch error that we see in a switch. Below is an example of how it is shown in Log :
24-June-2020 12:11:04 %CDP-W-NATIVE_VLAN_MISMATCH:
After the above syntax, you will see the details of the actual Port on which you see this message.
Reason for this message
By default, switches use VLAN 1 as native Vlan to forward untagged traffic to pass through the Trunk link configured between Switches. Untagged traffic is the traffic that doesn’t below to any VLAN configured on the switch. When you have different Vlan ID (native VLAN ) configured on both switches for untagged traffic you receive this error message in Logs.
Conclusion
In a lab environment, a native VLAN mismatch can be annoying but doesn’t affect functionality you are testing. However, in a production environment, a native VLAN mismatch can be extremely difficult to track down if it is at play and can potentially cause major outages if untagged traffic isn’t passed as expected.
Best practice
Always change the Native VLAN ID on switches to some other ID than default VLAN 1.