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Redundancy, symmetry, and load balancing are
crucial needs facing anyone in the process of implementing a
high-throughput connection to the Internet. ISPs and their large customers
require adequate control over how traffic enters and exits their
respective autonomous systems.
Redundancy is achieved by providing
multiple alternate paths for the traffic, usually by having multiple
connections to one or more autonomous systems. Symmetry exists if traffic
leaves the AS from a certain exit point and returns through the same
point. Load balancing, as you have seen, results in the division of
traffic optimally over multiple links. Together, these three requirements
can be difficult to meet in a BGP environment because any provider between
the source and destination of a packet can affect its path.
The general design problem of how best to
implement redundancy, symmetry, and load balancing is common to every
network. The specific solution, however, depends on an individual
network's needs and unique configuration. The following sections examine
the general design issues: redundancy, symmetry, and load balancing, as
well as configuration models for successful implementation.
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