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Ethernet Ports
ROS™ v3.5 102 RS400
3.2.4 Link Detection Options
Figure 70: Link Detection Form
Fast Link Detection
Synopsis: { Off, On, On_withPortGuard }
Default: On_withPortGuard
This parameter provides system protection against a faulty end device generating an improper
link integrity signal. When a faulty end device or a mismatched fiber port is connected to the
unit, a large number of continuous link state changes can be reported in a short period of time.
This large rate of link state changes can render the system unresponsive as most of the system
resources are used to process the link state changes. This could in turn cause a serious
network problem as the unit's STP process might not be scheduled enough time to run, thus
allowing the potential for network loops to form.
Three different settings are available for this parameter:
ON_withPortGuard - This is the recommended setting. With this setting, an extended period
(>2 minutes) of excessive link state changes reported by a port will prompt the Port Guard
feature to disable Fast Link Detection on that port permanently and to raise an alarm. By
disabling Fast Link Detection on the port, excessive link state changes can no longer consume
a substantial amount of system resources. Note, however, that if Fast Link Detection is
disabled, the port will need a longer time to detect a link failure. If the port is part of a spanning
tree, this could result in a longer network recovery time, of up to 2s. Once Port Guard has
disabled Fast Link Detection on a particular port, the user can re-enable it by clearing the alarm.
ON - In certain special cases where prolonged, frequent link state change constitutes legitimate
link operation, using this setting prevents the system from disabling Fast Link Detection on the
port in question. If excessive link state changes persist for more than 2 minutes on a particular
port, an alarm will be generated to warn about the observed bouncing link. If the condition of
excessive link state changes is resolved later on, the alarm will be cleared automatically. Since
this option does not disable Fast Link Detection, a persistent bouncing link could affect the
response time of the system. This setting should be used with caution.