Set a port to trunk mode when connecting switches or routers. You can allow all VLANs or specify which VLANs traverse the trunk. Limiting VLANs improves security. If switches A and B don't need VLAN , don't allow it on their trunk. You should also explicitly set the native VLAN rather than accepting the default. Configure both ends identically to avoid mismatches.
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$ curl repovive.com/roadmaps/network-design/switching-and-vlans/configuring-trunk-ports
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