The Lazy Networker

Update: frequency of updates, default 30 seconds.

Invalid: seconds since a valid update was seen, to consider the route invalid and placing the route into hold down, default is 180 seconds, in other words six updates. After 180 seconds the route is considered invalid – unreachable (metric is 16).

Hold Down: Once in hold down, how long (in seconds) to “not believe” any equal or less impressive (worse) route updates for routes that are in hold down, default is 180 seconds.

Flush: how many seconds, since the last valid update, until we throw that route in the trash (garbage collection for un-loved non-updated routes)

Defaults are(in seconds), here is what ciscopress says:Update: 30 Invalid: 180 Hold Down: 180 Flush: 240

The Invalid and Holddown Timers start together and have the same default value, what it means is, if a router does not receive any update for 180 seconds – it is considered invalid and during the same time (at least during the wait for an update) the holddown timers is also ticking and will not accept a worse update. The Flush Timers (after 180 seconds) will allow the better metric route to get entered during last 60 seconds and after waiting for 240 seconds since the last update, the route will be flushed from the route table.