ECS4110-28P_Management Guide

C HAPTER 8 | Spanning Tree Algorithm
Configuring Global Settings for STA
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◆ Transmission Limit – The maximum transmission rate for BPDUs is
specified by setting the minimum interval between the transmission of
consecutive protocol messages. (Range: 1-10; Default: 3)
When the Switch Becomes Root
◆ Hello Time – Interval (in seconds) at which the root device transmits a
configuration message.
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Default: 2
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Minimum: 1
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Maximum: The lower of 10 or [(Max. Message Age / 2) -1]
◆ Maximum Age – The maximum time (in seconds) a device can wait
without receiving a configuration message before attempting to
reconverge. 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. (References to “ports” in this section mean “interfaces,” which
includes both ports and trunks.)
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Default: 20
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Minimum: The higher of 6 or [2 x (Hello Time + 1)]
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Maximum: The lower of 40 or [2 x (Forward Delay - 1)]
◆ 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.
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Default: 15
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Minimum: The higher of 4 or [(Max. Message Age / 2) + 1]
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Maximum: 30
RSTP does not depend on the forward delay timer in most cases. It is
able to confirm that a port can transition to the forwarding state
without having to rely on any timer configuration. To achieve fast
convergence, RSTP relies on the use of edge ports, and automatic
detection of point-to-point link types, both of which allow a port to
directly transition to the forwarding state.
Configuration Settings for MSTP
◆ Max Instance Numbers – The maximum number of MSTP instances
to which this switch can be assigned.
◆ Configuration Digest – An MD5 signature key that contains the VLAN
ID to MST ID mapping table. In other words, this key is a mapping of all
VLANs to the CIST.