The Final Decision on What Routes Populate the Routing Table

The Final Decision on What Routes Populate the Routing Table
There are a couple of different factors that make the final decision on what routes will be placed
in the routing table, namely, administrative distance and metric, assuming that no route filtering
is in place that would specifically prevent a route from being placed in the routing table. The
first factor to be taken into consideration when making the decision of what route to place in
the routing table is administrative distance.
What is administrative distance? Administrative distance (AD) is the trustworthiness of the
routing protocol that produced the route. Administrative distance can be any value between 0
and 255. The lower the number, the more trustworthy the source of the route.
Table 1.3 shows the default administrative distance that a Cisco router will use to decide the
best route to a destination.