Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 472)

Spanning Tree Introduction: STP, RSTP, and MSTP
Software Reference for x310 Series Switches
18.4 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
The logical spanning tree, sometimes called the active topology, includes the root bridge
and all designated bridges, meaning all ports that are to be used for communication
within the spanning tree. These ports are in the forwarding state. Ports removed from the
logical spanning tree are not in the forwarding state. To implement the spanning tree
algorithm, devices communicate with one another using the Spanning Tree Protocol.
Spanning tree modes
STP can run in one of three modes: STP, RSTP or MSTP. A device running RSTP is compatible
with other devices running STP; a device running MSTP is compatible with other devices
running RSTP or STP. By default, on a device in MSTP mode each port automatically
detects the mode of the device connected to it (MSTP, RSTP or STP), and responds in the
appropriate mode by sending messages (BPDUs) in the corresponding format. Ports on a
device in RSTP mode can automatically detect and respond to connected devices in RSTP
and STP mode. Particular ports can also be forced to only operate in a particular mode
(
spanning-tree force-version command on page 19.42 ).
STP The Spanning Tree Protocol (STP) is the original protocol defined by IEEE standard
802.1D-1988. It creates a single spanning tree over a network.
STP mode may be useful for supporting applications and protocols whose frames may
arrive out of sequence or duplicated, for example NetBeui.
RSTP Rapid Spanning Tree Protocol (RSTP) also creates a single spanning tree over a network.
Compared with STP, RSTP provides for more rapid convergence to an active spanning tree
topology. RSTP is defined in IEEE standard 802.1D-2004.
By default, the device operates in RSTP mode.
MSTP The Multiple Spanning Tree Protocol (MSTP) addresses the limitations in the previous
spanning tree protocols, STP and RSTP, within networks that use multiple VLANs with
topologies that employ alternative physical links. It supports multiple spanning tree
instances on any given link within a network, and supports large networks by grouping
bridges into regions that appear as a single bridge to other devices.
MSTP is defined in IEEE standard 802.1Q-2005. The protocol builds on, and remains
compatible with, the previous IEEE standards defining STP and RSTP.