A routing protocol's capability 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 can be used. Another
advantage is that maintaining multiple routes to a single destination
reduces a network's 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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