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Chapter 3 General Management of the Switch 3-71
The following global STA paramters are fixed and cannot be changed:
■ Bridge ID – The priority and MAC address of the switch.
■ Designated Root – The priority and MAC address of the device in the spanning
tree that the switch has accepted as the root device.
■ Root Port – The number of the port on the switch that is closest to the root. The
switch communicates with the root device through this port. If there is no root
port, then the switch has been accepted as the root device of the spanning tree
network.
■ Root Path Cost – The path cost from the root port on the switch to the root
device.
■ Root Hello Time – The interval (in seconds) after which the current root device
transmits a configuration BPDU frame.
■ Root Maximum Age – The maximum time (in seconds) the switch can wait
without receiving a configuration message before attempting to reconfigure.
All switch ports (except for designated ports) should receive configuration
messages at regular intervals. If the root port ages out STA information
(provided in the last configuration message), a new root port is selected from
among the switch ports connected to the network. (References to “ports” in
this section means “interfaces,” which includes both ports and aggregated
links.)
■ Root Forward Delay – The maximum time (in seconds) the switch waits before
changing states (for example, from discarding 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
discarding state; otherwise, temporary data loops might result.
■ Root Hold Time – The interval (in seconds) during which no more than two
configuration BPDUs shall be transmitted by the switch.
The following root device global parameters can be configured:
■ Priority – The bridge priority that is used in selecting the root device, root port,
and designated port. The device with the highest priority becomes the STA root
device (0=highest, 61440=lowest). However, if all devices have the same priority,
the device with the lowest MAC address will then become the root device.
Specify a value from 0 to 61,440 in steps of 4096. The possible options are 0, 4096,
8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248,
57344, and 61440. The default is 32,768.
■ Hello Time – The interval (in seconds) after which the switch transmits a
configuration BPDU frame when it becomes the root device.
Specify a value from 1 to the lower of 10 or [(Max. Message Age / 2) -1]. The
default is 2 seconds.