STA (Spanning Tree Algorithm)3-19When the Switch Becomes Root
Parameter Default Description
Hello Time 2 The time interval (in seconds) at which the root device
transmits a configuration message.
The minimum value is 1.
The maximum value is the lower of
10 or [(Max. Message Age / 2) -1].
Max (Message) Age 20 The maximum time (in seconds) a device can wait
without receiving a configuration message before
attempting to reconfigure. All device ports (except for
designated ports) should receive configuration
messages at regular intervals. Any port that ages out
STA information (provided in the last configuration
message) becomes the designated port for the attached
LAN. If it is a root port, a new root port is selected from
among the device ports attached to the network.
The minimum value is the higher of
6 or [2 x (Hello Time + 1)].
The maximum value is the lower of
40 or [2 x (Forward Delay - 1)].
Forward Delay 15 The maximum time (in seconds) the root device will wait
before changing states (i.e., listening to learning to
forwarding). This delay is required because every
device must receive information about topology
changes before it starts to forward frames. In addition,
each port needs time to listen for conflicting information
that would make it return to a blocking state; otherwise,
temporary data loops might result.
Maximum value is 30.
Minimum value is the higher of 4 or
[(Max. Message Age / 2) + 1].