Highly Available Networks

as duplicate IP addresses are avoided.
For customers who are not concerned about maximizing network throughput and do not want to take on
the task of configuring gated on all their systems, the default route set to local will work as an
alternative. Configure each local node as the default router and it will broadcast all IP packages destined
for the other subnets.
Highly Available Star Topologies
In the Star topology section at the beginning of this paper, we learned the hub or the concentrator is a
SPOF for the LAN. Implementing duplicate stars removes this SPOF. Just as discussed in the previous
section on increased bus availability, a hub or concentrator failure will cause the biggest percentage of
communication outage. The cable has been changed from a high impact point to a low impact point,
because all cables are point to point instead of having multiple taps as in the bus configurations.
Figure 12: Highly Available Star Topology
In Figure 12, there are two ethernet cards on each system using twisted-pair cabling. The first ethernet
card is connected to the one hub, and the standby ethernet card is connected to the alternate hub. The
hubs are interconnected with one cable to make them one subnet. If a LAN card on a server fails, the
second LAN card will take over the communications.
Figure 13: Highly Available Star Topology with Routers