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Single-homed customers connect to the Internet
via one connection to a service provider (see the figure).
Within a single-homed AS, a static default
route is typically all that is needed to point traffic toward the provider.
And, as discussed in Chapter 8, the provider can use several methods to
learn and propagate routes to the customer's network, including static
routing. In the case of a single-homed AS, there is no issue of route
symmetry because traffic has a single entrance and a single exit point.
Moreover, redundancy and load balancing are not an issue. If the single
connection is lost, the customer must tolerate the outage until it is
repaired. Obviously, such an arrangement would not satisfy
mission-critical data communication requirements. An AS must be multihomed
to accommodate e-commerce and other mission-critical applications.
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