This is the algorithm that allows EIGRP to have all the features it has and allows traffic to be so reliable. The following is a list of the essential tasks that it does:
- Finds a backup route if the topology permits
- Support for VLSM
- Dynamic route recovery
- Query its neighbor routers for other alternate routes
EIGRP routers maintain a copy of all their neighbors' routes, so they can calculate their own cost to each destination network. That way, if the successor route goes down, they can query the topology table for alternate or backup routes. This is what makes EIGRP so awesome, since it keeps all the routes from their neighbors and, if a route goes down, it can query the topology table for an alternate route.
But, what if the query to the topology table does not work? Well, EIGRP will then ask its neighbors for help to find an alternate...
