Once the router has performed these initial broadcasts and updated its routing information table, it is ready to accept routing requests and route packets. When a router receives information that causes it to change its routing information table, the router immediately passes that information on to its other directly connected network segments, except the segment from which the router received the information. The primary causes of a change in the network's configuration are file servers or external routers coming up or going down. If a router needs to be brought down, the router will inform its directly connected segments of the fact before discontinuing service. If a router goes down due to a hardware failure, power glitch, or power outage, other routers will not be notified that a change has occurred.
Routers maintain a timer for each entry in their routing information table.
Every time that information is received concerning the entry, the timer is reset to zero. If the timer reaches three minutes, the router assumes that the route to the network number is down and broadcasts that fact to its other segments. Because this information is new or changed, the routers that receive the information will pass it on immediately and the change will quickly permeate the network.