If switch A has native VLAN and switch B has native VLAN on their shared trunk, traffic leaks between VLANs. Untagged frames from A go to VLAN on B. Untagged frames from B go to VLAN on A. This breaks network segmentation and can create loops. Always ensure both ends of a trunk use the same native VLAN. Some switches warn you about mismatches via CDP or LLDP.
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$ curl repovive.com/roadmaps/network-design/switching-and-vlans/native-vlan-mismatch
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