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744 Chapter 12 • Operational and Organizational Security: Policies and Disaster Recovery

Consideration should also be given to methods of communication. Members of
the incident response team will not be able to coordinate their efforts, and func-
tions of the business may not operate properly, if people cannot talk to one
another. Imagine a police department that loses its radio system and officers are
unable to respond to calls or report on their situations.To deal with the possibility
of phone lines and other communication systems going down, administrators
should plan to use other systems. Mobile phones are one possibility, while sending
e-mails through high-speed broadband is another.The important thing is to have
an alternative system ready for when it is needed.

High Availability/Fault Tolerance

A single point of failure can be the Achilles heel that brings down a system.
Imagine a single road with a bridge that provides the only way to enter or exit a
town. If the bridge fell down, no one would be able to enter or leave the town. Just
as the bridge provides a single point of failure that can cut people off from the out-
side world, a single point of failure in a system can sever a company’s ability to per-
form normal business functions.
High availability is provided through redundant systems and fault tolerance. If
the primary method used to store data, transfer information, or other operations
fails, then a secondary method is used to continue providing services.This ensures
that systems are always available in one way or another, with minimal downtime to
prevent people from doing their jobs.
Redundancy is often found in networks, such as when multiple links are used
to connect sites on a WAN. Network lines may be used to connect two sites, with
a separate network line set up in case the first goes down. If this first link fails, the
network can be switched over to use the second link. In other instances, additional
lines may be set up in other ways to provide redundancy. For example, site A is
connected to site B, which is connected to site C.These two links connect the
three sites together, but if either of them fails, one of the sites will be unable to
communicate with the others, and vice versa.To provide high availability, a third
link can be set up between sites A and C.As shown in Figure 12.4, the additional
link allows the three sites to communicate with one another if any one link fails.

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