RSTP uses type 2, version 2 BPDUs. The original 802.1D STP uses type 0, version 0 BPDUs. However, a switch running RSTP can communicate directly with a switch running the original 802.1D STP. RSTP sends BPDUs and populates the flag byte in a slightly different manner than in the original 802.1D:

Note: Like STP, an RSTP switch sends a BPDU with its current information every Hello time period (two seconds, by default), even if the RSTP bridge does not receive any BPDUs from the root bridge.

As shown in the figure, RSTP uses the flag byte of version 2 BPDU: