quote of the day...

ravi malhotra

or notsohotra...

from ip routing http://oreilly.com/catalog/iprouting/chapter/ch04.html#71987

 If a reported distance for a destination is less than the feasible distance for the same destination, the router that advertised the RD is said to satisfy the feasibility condition (FC) and is referred to as a feasible successor (FS).

as if you haven't read that enough times... READ IT AGAIN...

Any of the following events can cause DUAL to reevaluate its feasible successors:

• The transition in the state of a directly connected link
• A change in the metric of a directly connected link
• An update from a neighbor

 If DUAL finds a feasible successor in its own topology table after one of these events, the route remains in passive state. If DUAL cannot find a feasible successor in its topology table, it will send a query to all its neighbors and the route will transition to active state.