RuggedCom RS400 manual Link Detection Options, Fast Link Detection

Ethernet Ports

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.

ROS™ v3.5 102 RS400