A/B SWITCH WITH REMOTE INTERFACE
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A/B Switch receives a command from the Ethernet network interface or from the serial RS232 interface. In addition
the STATUS LED will blink when a switching command is issued via the remote control contacts or front panel
push button switches.
The A/B Switch also has the ability to issue either SNMP traps, or UDP syslog messages. These messages can be
sent to one or more network administrator systems to provide notification when the A/B Switch changes connection
states either automatically (auto bypass switching or auto recovery switching) or via manual control (front panel
toggle switch or commands received on the RS232 or Ethernet interfaces), and when certain other events occur. See
section 10 and section 11 for additional details.
To restrict access to the A/B Switch, each of the Ethernet interface options (SNMP, telnet, and web browser) can be
independently enabled/disabled, and if enabled, can be configured to require a login password. Additionally, user
access can be restricted by IP address so only commands received from pre-defined “administrator” IP addresses
will be acknowledged and acted upon. See section 7 for additional information regarding these commands.
5.5 Automatic Switching
The A/B Switch models that support Ethernet remote control can also be configured to automatically switch
between a “normal” connection state (port C connected to port B) and a “bypass” or “failover” connection state (port
C connected to port A). User configurable failover and recovery parameters control the auto-switching functions to
allow the switch to be used in a variety of applications. In order to be able to perform the auto bypass and auto
recovery switching functions, the A/B Switch issues ICMP echo request (PING) packets from its Ethernet network
interface to a user configurable IP address on the network. If the “normal” network path connections between the
A/B Switch and the device being monitored go down for any reason, the A/B Switch will no longer be able to PING
the specified IP address, and will then automatically switch from the “normal” connection state (port C connected to
port B) to the “bypass” or “failover” connection state (port C connected to port A). Once the problems on the
primary path have been identified and corrected, the user can issue a command to cause the A/B Switch to switch
from the failover connection state back to the normal connection state. If auto recovery is enabled, the A/B Switch
will automatically re-connect the normal path connections when it is again able to PING the user specified IP
address. When using the auto recovery feature, it is important that the Ethernet network port on the A/B Switch be
connected to the user’s network such that the normal path is continuously being monitored even when the backup
path has been selected, otherwise the A/B Switch could repeatedly switch (flap) back and forth between the failed
primary path and the functioning backup path. See the diagrams below for examples of auto switching
configurations.
Auto Failover & Manual Recovery
1.1.10.1
A/B Switch
PING 2.2.20.1
C
A
B
Network
Port
Network 1
primary
WAN
Note: The A/B Switch monitors the WAN
connections by PINGing the far side router
thru the primary WAN link. If the primary WAN
link fails, the A/B Switch auto switches to the
backup WAN link. Auto recovery is disabled
in this configuration to prevent flapping.
router
2.2.20.1
primary
WAN
backup
WAN
backup
WAN
Network 2
router
