Detecting Loops - Hirschmann RS20 User Manual

Operation Diagnosis

9.9 Detecting Loops

Loops in the network, even temporary loops, can cause connection
interruptions or data losses. The automatic detection and reporting of this
situation allows you to detect it faster and diagnose it more easily.
An incorrect configuration can cause a loop, for example, if you deactivate
Spanning Tree.
The device allows you to detect the effects typically caused by loops and
report this situation automatically to the network management station. You
have the option here to specify the magnitude of the loop effects that triggers
the device to send a report.
A typical effect of a loop is that frames from multiple different MAC source
addresses can be received at different ports of the device within a short time.
The device evaluates how many of the same MAC source addresses it has
learned at different ports within a time period.
Note: This procedure detects loops when the same MAC address is received
at different ports. However, loops can also have other effects.
Conversely, the same MAC address being received at different ports can
also have other causes than a loop.
 Select the Switching:Global dialog.
 Select "Enable address relearn detection". Enter the desired
threshold value in the "Address relearn threshold" field.
If the address relearn detection is enabled, the device checks whether
it has repeatedly learned the same MAC source addresses at different
ports. This process very probably indicates a loop situation.
If the device detects that the threshold value set for the MAC addresses
has been exceeded at its ports during the evaluation period (a few
seconds), the device creates an entry in the log file and sends an alarm
(trap). The preset threshold value is 1.
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9.9 Detecting Loops
UM BasicConfig L2E
Release 8.0 05/2013