Siemens RUGGEDCOM ROS v4.3 User Manual page 94

Chapter 3
Device Management
3
Figure 30: Link Detection Form
1. Fast Link Detection Box 2. Link Detection Time Box 3. Apply Button 4. Reload Button
2. Configure the following parameter(s) as required:
NOTE
When Fast Link Detection is enabled, the system prevents link state change processing from
consuming all available CPU resources. However, if Port Guard is not used, it is possible for almost
all available CPU time to be consumed by frequent link state changes, which could have a negative
impact on overall system responsiveness.
Parameter
Fast Link Detection
78
Description
Synopsis: { Off, On, On_withPortGuard }
Default: On_withPortGuard
This parameter provides protection against faulty end devices
generating an improper link integrity signal. When a faulty end
device or a mis-matching fiber port is connected to the unit, a
large number of continuous link state changes could be reported
in a short period of time. These large number of bogus link state
changes could render the system unresponsive as most, if not
all, 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 RSTP process may not be able to run, thus allowing
network loop 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 Port Guard feature to
disable FAST LINK DETECTION on that port and raise an alarm.
By disabling FAST LINK DETECTION on the problematic port,
excessive link state changes can no longer consume substantial
amount of system resources. However if FAST LINK DETECTION
is disabled, the port will need a longer time to detect a link
failure. This may result in a longer network recovery time of
up to 2s. Once Port Guard disables FAST LINK DETECTION of a
particular port, user can re-enable FAST LINK DETECTION on the
port by clearing the alarm.
• ON - In certain special cases where a prolonged excessive link
state changes constitute a legitimate link operation, using
this setting can prevent Port Guard from disabling FAST LINK
DETECTION on the port in question. If excessive link state
changes persist for more than 2 minutes, an alarm will be
generated to warn user about the observed bouncing link. If
the excessive link state changes condition is resolved later on,
the alarm will be cleared automatically. Since this option does
not disable FAST LINK DETECTION, a persistent bouncing link
RUGGEDCOM ROS
User Guide
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Configuring Link Detection