Internet Routing Architectures, Second Edition

Redundancy

Although corporations and providers would prefer uninterrupted connectivity, connectivity problems occur for one reason or another from time to time. Connectivity is not the responsibility of one entity. A router's connection to the Internet involves the router, the CSU/DSU, power, cabling, physical access line, and numerous administrators—each with influence over different parts of the connection. At any time, human error, software errors, physical errors, or adverse unforeseen conditions (such as bad weather or power outages) can jeopardize connectivity.

For all these reasons, redundancy is generally desirable. Finding the correct balance between redundancy and symmetry, however, is critical. Redundancy and symmetry can be conflicting ...