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852-1328
Configuration in the WBM
Note
If the management VLAN is not configured as an access port on the switch, the configu-
ration must be accessed via the trunk port. In this case, the configuration must be per-
formed via an access port of a second switch that is located in the same management
VLAN.
10.7 Redundancy
10.7.1 RSTP
10.7.1.1 General Information
The Rapid Spanning Tree Protocol (RSTP) is a development of the Spanning Tree Proto-
col (STP). Both protocols are defined by the IEEE in the following standards:
• IEEE 802.1D: Spanning Tree Protocol
• IEEE 802.1w: Rapid Spanning Tree Protocol
RSTP can detect and break network loops and provide backup links (spare connections)
between switches, bridges or routers. By regularly exchanging Bridge Protocol Data Units
(BDPU), a switch can interact with other RSTP-capable switches in the network to ensure
that only one connection exists between any two stations in the network at any given
time.
Compared to STP, RSTP allows faster adaptation of the spanning tree. It is also back-
ward compatible with STP-only bridges. With RSTP, information about changes in topol-
ogy is broadcasted throughout the network directly from the device generating the
change. With STP, a longer delay is required because the device causing a topology
change first notifies the root bridge, which in turn notifies the rest of the network. Both
RSTP and STP remove unwanted learned addresses from the filter database.
To create the spanning tree, a root bridge must be selected first. This is the starting point
of a spanning tree. Starting from the root bridge, , all paths are defined via which the
other bridges in the
network can be reached. The root bridge is selected according to a defined procedure.
For this purpose, the switches exchange their Bridge-ID (BID - consisting of priority, sys-
tem ID and MAC address) via multicast messages and select the switch with the lowest
priority as the root bridge of the spanning tree. If the lowest priority is assigned to more
than one switch, other criteria such as the MAC address are decisive.
After the root bridge has been selected, the paths through which the other bridges in the
network can be reached are defined. For this purpose, all paths on which other switches
can be reached are first determined. If several paths are recognized over which a switch
can be reached, the paths with the least favorable path costs are blocked. The path costs
are the costs for transmitting a frame through the port in the LAN. The IEEE standard de-
fines the path costs, but also allows them to be set manually. This value should be ad-
justed to the transmission speed. The valid range is 1 to 200000000. A path with higher
costs is more likely to be blocked by STP if a network loop is detected.
Product manual | Version: 1.2.0
73
Industrial Managed Switch
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