User manual

(Rapid) Spanning Tree
6874_en_09 PHOENIX CONTACT 5-15
5.2.5 Configuration Notes for Rapid Spanning Tree
In contrast to the Spanning Tree method, the Rapid Spanning Tree method supports
event-controlled actions that are no longer triggered based on a timer.
If one cable fails (link down), the Rapid Spanning Tree method can respond more quickly
to this failure and thus the switch-over time can be kept low.
– For short switch-over times, structure your network in such a way that a maximum of
seven switches are located in a cascade up to the root switch. The switch-over times
can range from 100 ms to 2 s.
– Use priority assignment to specify a central switch as the root.
– It is also recommended to assign a switch as the backup root.
– For short switch-over times, all switches in the redundant topology should support the
Rapid Spanning Tree Protocol and should not use hubs.
5.2.5.1 Connecting the Switches to Form a Meshed Topology
Having activated (Rapid) Spanning Tree for all switches, you can create a meshed
topology with redundant data paths. Any data connections can now be created without
taking loops into consideration. Loops can even be added on purpose in order to create
redundant connections.
A data path between Spanning Tree switches can be:
– A direct connection.
– A connection via one or more additional switches that do not support Spanning Tree.
– A connection via one or more additional hubs that do not support Spanning Tree.
Furthermore, a data path can also consist of a connection of a Spanning Tree switch to:
– A termination device.
– A network segment in which no loops may occur, which consists of several
infrastructure components (hubs or switches) without Spanning Tree support.
A link down or link up must be detected at the switch so that the RSTP switches can
detect a line failure and a restored line more quickly. Please take into consideration, in
particular, paths where media converters are used. If required, media converters offer
setting options to transmit the link status of the fiber optic side to the twisted pair side.
If a link down is not detected at the switch, due to the cable interrupt between the media
converters, and if no link down is forced at the switch, timer-based detection is activated,
which may result in longer switch-over times.
If Spanning Tree is not supported by all of the switches used, the reconfiguration time for
Spanning Tree is extended by the aging time of switches without Spanning Tree support.