C
HAPTER
4
| Configuring the Switch
Configuring the Spanning Tree Algorithm
– 77 –
CONFIGURING GLOBAL
SETTINGS FOR STA
Use the RSTP System Configuration page to configure settings for STA
which apply globally to the switch.
PARAMETERS
The following parameters are displayed on the RSTP System Configuration
page:
◆ System Priority – Bridge priority is used in selecting the root device,
root port, and designated port. The device with the highest priority
becomes the STA root device. However, if all devices have the same
priority, the device with the lowest MAC address will then become the
root device. Note that lower numeric values indicate higher priority.
(Options: 0-61440, in steps of 4096; Default: 32768)
◆ Max Age – 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. (Note that
references to “ports” in this section mean “interfaces,” which includes
both ports and trunks.)
Minimum: The higher of 6 or [2 x (Hello Time + 1)]
Maximum: The lower of 40 or [2 x (Forward Delay - 1)]
Default: 20
◆ Forward Delay – The maximum time (in seconds) this device will wait
before changing states (i.e., 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.
Minimum: The higher of 4 or [(Max. Message Age / 2) + 1]
Maximum: 30
Default: 15
◆ Transmit Hold Count – The number of BPDU's a bridge port can send
per second. When exceeded, transmission of the next BPDU will be
delayed. (Range: 1-10; Default: 6)
◆ Protocol Version – Specifies the type of spanning tree used on this
switch. (Options: Normal – RSTP, or Compatible – STP;
Default: Normal)
RSTP supports connections to either RSTP or STP nodes by monitoring
the incoming protocol messages and dynamically adjusting the type of
protocol messages the RSTP node transmits, as described below:
RSTP Mode - If RSTP is using 802.1D BPDUs on a port and receives an
RSTP BPDU after the migration delay expires, RSTP restarts the
migration delay timer and begins using RSTP BPDUs on that port.
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