Allied Telesis AT-9000 Series - Manual (Page 598)

Chapter 40: STP, RSTP and MSTP Protocols
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Mixed STP and RSTP Networks
RSTP IEEE 802.1w is fully compliant with STP IEEE 802.1d. A network
can have both protocols. If both RSTP and STP are present in a network,
they operate together to create a single spanning tree domain. Given this,
if you decide to activate spanning tree on the switch, there is no reason
not to use RSTP, even if the other switches are running STP. The switch
combines its RSTP with the STP on the other switches by monitoring the
traffic on the ports for BPDU packets. Ports that receive RSTP BPDU
packets operate in RSTP mode while ports receiving STP BPDU packets
operate in STP mode.