Figure 99: Router Redundancy with two paired L-IP Redundant routers
During power-up the two L-IP Redundant routers automatically negotiate, which one
becomes the active router (primary router) and which one the inactive standby router
(secondary router)
. The active router forwards packets, performs bus loop monitoring, and
has node monitoring enabled, while the inactive devices has all these functions disabled.
After this initial startup-phase the devices periodically monitor each other on the CEA-709
and on the CEA-852 (IP) side. If the secondary router no longer reaches the primary router
on either side it becomes active and issues an alarm, if the primary router no longer reaches
the secondary router just an alarm is issued.
Further, the secondary device, even though it is inactive and does not forward packets, it
counts the number it would forward based on the packets it receives and on its routing
tables. Now the two devices periodically compare these numbers and if these numbers
significantly differ over multiple monitoring intervals an alarm is issued. This algorithm
ensures that the routing tables of both devices are consistent and the secondary router is
correctly configured and able to take over if the primary device fails. Further, if the primary
device does not forward any packets in one direction, while the secondary would forward
packets the secondary devices takes over and the primary device becomes inactive.
Router redundancy can be used with or without bus loop monitoring enabled (see Section
9.2.1).
To enable router redundancy both routers must be commissioned and added to the same
IP-852 channel. Further, the two routers must be linked by binding certain network
variables, which are used for communication between the two paired L-IP Redundant
routers. Please see Section 9.4.3.2 on how to configure the L-IP Redundant for router
redundancy.
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