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The capability of a routing protocol to
update and calculate routes efficiently is based on several factors:
- Whether the protocol calculates and
stores multiple routes to each destination
- The manner in which routing updates
are initiated
- The metrics used to calculate
distances or costs
The following sections discuss these three factors in detail.
Multiple routes to a single destination
Some routing protocols allow the router to install only a single route
to a destination network in its routing table. Other routing protocols
permit the router to store multiple routes to each destination, at the
cost of additional overhead. One advantage of multiple routes is that
equal-cost load balancing or unequal-cost load balancing may be used.
Another advantage is that maintaining multiple routes to a single
destination reduces the network vulnerability to routing loops and
dropped packets when a link fails. If a router maintains two different
routes to 10.0.0.0 and one route fails, the router can continue to
route to 10.0.0.0 using the second route, without waiting for an
alternate route to propagate. Maintaining multiple routes does not
reduce convergence time, but it can insulate a router from
instabilities during the convergence process.
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