
Interface Redundancy Overview
114079 Rev. B
1-3
During normal data transfer, if the active interface fails, the following interfaces
become active, in this order:
1. Redundant interfaces on the slot that is processing the routing/bridging table
for this circuit
2. Redundant interfaces on other slots
BOFL Parameters and Role Change Speed on Ethernet
When you enable BOFL, the router only sends BOFL messages if the interface is
idle. If the interface is transmitting regular data traffic, it does not send BOFL
messages.
Three parameters control BOFL. The BOFL Retries parameter sets the number of
BOFL messages the interface transmits before the router declares the circuit
down. The number of seconds between BOFL messages is the value of the BOFL
Timeout parameter divided by the BOFL Timeout Divisor parameter.
To increase the speed of detecting failed interfaces and changing roles on Ethernet
connectors, set the BOFL Timeout parameter to a short interval, such as 1 second.
If you also set the BOFL Retries parameter to 4, and accept the BOFL Timeout
Divisor parameter default value of 1, a role change occurs in under 5 seconds. If
you set the BOFL Timeout Divisor parameter to a higher value, the router sends
BOFL messages so frequently that the cost in LAN bandwidth and CPU overhead
is high.
Refer to Appendix D for parameter descriptions and instructions for using Site
Manager to edit these parameters.
Hot and Warm Standby
When a redundant interface takes over for a failed interface without interruption in
service, it does so under one of two conditions: hot standby or warm standby.
Hot Standby
When an active interface fails, but the circuit is still up, the new active interface
retains access to the routing/bridging tables, and can continue transmission
immediately.
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