9.5 Redundancy, Symmetry, and Load Balancing
9.5.6
Redundancy, symmetry, and load balancing in a single-homed AS
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.