adept technology GadgetGateway User Manual page 20

GadgetGateway Overview
2.5 Redundant Twin Mode
Although 709.1 and some network management tools allow for a pair of conventional
709.1 routers to be identically configured and connected between the same two channels,
this configuration induces a doubling of the traffic between those two channels. The built-
in duplicate detection mechanism in 709.1 discards the duplicate packets at each receiving
node. However, the extra traffic (double) could tax network bandwidth and create other
problems.
In Twin Redundant Mode both routers are identically configured 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. This feature achieves the increased system reliabil-
ity of having a redundant backup router without the drawbacks of doubled traffic. The
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, diag-
nosed, 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 traf-
fic until the fault has been healed.
In addition, the router configuration is periodically automatically synchronized between
the two routers to reduce fail-over time and increase the fidelity between the backup and
primary router operation. Also supported is manual synchronization which makes it more
convenient to field replace one of the redundant pair and replicate its configuration. A high
2-10