Network Router User Manual

1.7. Redundant Twin Mode
e Twin Redundant Mode enables two GRouter devices to operate as a redundant pair for high
availability applications without generating duplicate trac. is enhanced capability increases
reliability and eliminates some single mode failure sources. A simple diagram showing a
redundant connection between two channels is shown below.
Router
IP/LON
709 with
852
709 with
LON
Ethernet
FTT-10
Router
IP/LON
709 with
852
709 with
LON
Ethernet
FTT-10
IP Ethernet Channel
709.1 FTT-10 Channel
Fig.1.11: Two redundant routers between the same channels
Although it is possible for a pair of conventional 709.1 routers to be identically congured and
connected between the same two channels, this conguration induces a doubling of the trac
between those two channels. e built-in duplicate detection mechanism in 709.1 discards the
duplicate packets at each receiving node. However, the doubled trac load could tax network
bandwidth and create other problems.
In Redundant Twin Mode (or for the sake of brevity, Twin Mode), both routers are identically
congured and connected between the same two channels as per the case described above but
unlike the case above only one of the two routers is forwarding packets. is feature achieves the
increased system reliability of having a redundant backup router without the drawbacks of
doubled trac. e Twin Mode routers monitor each others health and operational status and
dynamically activate forwarding as needed should one of the other fail. Failures are detected,
diagnosed, and reported so that repairs can be made to maintain continuous availability. Should
there be a fault in either interface then both routers will go active and forward trac until the
fault has been healed. In addition, the router conguration is periodically automatically
synchronized between the two routers to reduce fail-over time and increase the delity between
the backup and primary router operation. Also supported is manual synchronization which
makes it more convenient to replace one of the redundant pair and replicate its conguration. A
high availability building network can be constructed using pairs of redundant twin mode routers
and a redundant switched ethernet network. An example network showing the application of
Twin Mode is shown below.
-15-