User manual

Rapid Spanning Tree
7278_en_01 PHOENIX CONTACT 4-13
4.2.1.10 Disabling the Spanning Tree Protocol/Using the Fast Forwarding
Function
4.2.1.11 Modifying the Protocol Timer
It may be necessary to modify the protocol timer if, e.g., there are more than ten active
Spanning Tree components in a single network. You can also attempt to reduce the
reconfiguration times by modifying the timer. However, care should be taken in order to
prevent unstable networks.
Please note that the protocol times are specified by the root switch and that they are
distributed to all devices via BPDU. It is therefore only necessary to modify the values in
the root switch. If the root switch fails, the timer values of another active STP switch (i.e.,
the new root switch) will be valid for the entire network segment. Please remember this
during component configuration.
Specifying the Timer Values
– Maximum number of active Spanning Tree components along the path beginning at
the root switch (please refer to the following two example illustrations):
= (MaxAge/2) - Hello Time + 1
– 2 x Forward Delay - 1 s ≥ MaxAge
–MaxAge ≥ 2 × Hello Time + 1 s
The value ((MaxAge/2) - Hello Time) for a ring topology corresponds to the maximum
number of components with active Spanning Tree.
One of the following requirements must be met so that the Spanning Tree Protocol can
be disabled for a port:
– A termination device is connected to the port.
– Additional infrastructure components are connected to the port. The corresponding
network segment does not contain any loops.
– Additional infrastructure components are connected to the port, forming a Spanning
Tree of their own. No additional redundant connections to this network segment are
permitted.
Modifying the protocol timer may result in unstable networks.