STP - BPDUs, VLAN IDs, and PVST+
When deploying PVST+ as the Spanning Tree Protocol (STP) on a switch, a separate STP instance is created for each VLAN. That means that BPDUs are also generated on a per-VLAN basis.
So how do switches know which BPDUs are for which VLAN?
BPDUs do not include the VLAN ID in their headers, but they are are sent inside VLAN-tagged Ethernet frames. The VLAN ID is included in the Ethernet frame, not in the BPDU itself. When a switch receives a BPDU, it determines the associated VLAN by examining the VLAN ID in the Ethernet frame.
Links:
https://forum.networklessons.com/t/per-vlan-spanning-tree-pvst/1112/71?u=lagapidis
https://networklessons.com/spanning-tree/per-vlan-spanning-tree-pvst/