HP 600 Series, Services And Applications

Page: 197 / 316

Improving Network Availability
Updated 7/93
For companies that rely heavily on network applications, a failure in the
network can be disastrous. Network failures are more likely to occur as
networks grow—the natural result of employing more and more network
equipment. This application note examines some of the methods for
increasing network availability (uptime) in router-based networks and
thereby reducing or eliminating user-perceived network failures.
The most common technique for increasing network availability is to
provide alternate paths for data in the event of link or router failures. This
plays to the strength of routers—quickly detecting network failures and
routing data around them. This application note examines the different ways
of providing alternate data paths to survive both data-link and router failures.
Permanent Alternate Paths
Consider the network in figure 1. There is only one path for data from any site
to any other site. Should link 1 fail, for instance, systems at site A will be unable
to communicate with systems at either site B or site C, until link 1 has been
restored. Adding a third link, as indicated by the dotted line between the site
A and site C routers, provides an alternate path for data to and from sites A and
C. Once the third link has been installed, any single link failure will not result
in a user-perceived network failure.
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