Network structures and network configuration
2.3 Media redundancy
Industrial Ethernet
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● Alternative port (substitute for the root port)
A substitute for the root port is configured. If the connection to the root bridge is lost, the
device can establish a connection over the alternate port without any delay due to
reconfiguration.
● Reaction to events
A Rapid Spanning Tree reacts to events, such as a connection abort, without delay.
There is no waiting for timers as in spanning tree.
● Counter for maximum number of bridge hops
The number of bridge hops a package is allowed to make before it automatically
becomes invalid.
In principle, in the case of Rapid Spanning Tree, alternatives for many parameters are
preconfigured and certain properties of the network structure are taken into account to
reduce the reconfiguration time.
Multiple Spanning Tree Protocol (MSTP)
MSTP is a further development of RSTP. MSTP is defined in the IEEE 802.1s standard,
subsequently IEEE 802.1Q.
Among other things, it provides the option of operating several RSTP instances or VLAN
groups within different virtual networks (VLAN - Virtual Local Area Network) so that, for
example, paths that would block the simple Rapid Spanning Tree Protocol for data traffic
globally can be available within individual VLANs.
2.3.10 RSTP+
2.3.10.1 Properties and functions of RSTP+
The main application of RSTP+ is the redundant integration of MRP rings into an RSTP
network. It is generally possible to manage such a network solely with RSTP. However, in a
ring topology, MRP is the more efficient and faster method. The MRP ring redundancy mode
is not affected by RSTP+ because both modes work independently of one another.
Another use case is the redundant linking of MRP rings. It is also possible to connect two
RSTP networks over one MRP ring with RSTP+. This is not possible without RSTP+
because Spanning Tree is disabled at the ring ports.
Compatibility of devices without RSTP+
In principle, all devices at the connection points between RSTP network and MRP ring must
support the RSTP+ method. All other devices in the MRP ring must forward BPDUs (Bridge
Protocol Data Unit).