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NBS008A
Chapter 5: Operation
To be able to perform the auto bypass and auto recovery sw itching functions, the switch issues ICMP echo request (PING ) packets
from its Ethernet network interface in order to determine if a path exists to an IP address specified during configuration of the
switch automatic switching feature. If the “normal” network path connections between the switch and the device being moni-
tored go down for any reason, the switch will no longer b e able to PING the specified IP address, and will then automatically
switch from the “normal” connection state (all COMMON ports connected to their respective B ports) to the “bypass” or
“failover” connection state (all COMMON ports are connected to their respective A ports) by internally executing a “SET SYSTEM
A” command. Once the problems on the primary path have been corrected, the user can issue a “SET SYSTEM B” command to
cause the switch to switch from the failover connection state back to the normal connection state. Or if auto recovery is enabled,
the switch will automatically re-connect the normal path connections (by internally executing a “SET SYSTEM B” command) when
it is again able to PING the user specified IP address. When using the auto recovery feature, make sure the Ethernet network por t
on the switch is connected to the user’s network so that the normal path is continuously being monitored even when the backup
path has been selected. Otherwise, the switch could repeatedly switch (flap) back and forth between the failed primary path and
the functioning backup path. See the following diagrams for examples of auto switching configurations.
Figure 5-1. Auto failover and manual recovery.
NOTE: The switch monitors the WAN connections by PINGing the far side router through the primary WAN link. If the primary
WAN link fails, the switch auto switches to the backup WAN link. Auto recovery is disabled in this configuration to prevent
flapping.
Figure 5-2. Auto failover and auto recovery.
NOTE: The switch monitors the WAN connections by PINGing the far side router through the primary WAN link. If the primary
WAN link fails, the switch auto switches to the backup WAN link. When the primary WAN link is available again, the
switch auto switches back to the primary WAN path.
The monitorip address and monitormac address parameters used by the automatic switching feature on the switch can be
configured to allow the switch to monitor connectivity to any device within or outside of the switch’s subnet. After you have
entered the monitorip address, you can either manually enter the monitormac address or allow the switch to determine it
automatically.