The regular updates in RIP is sent every 30 seconds by default. The details of the regular updates can be seen by giving the command "sh ip protocols".
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds, next due in 20 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
The above example shows that updates are sent every 30 seconds and its been 10 seconds since the last update and so the next update is due in 20 seconds...
Flash Updates sends new update as soon as a route fails. When you give the command "flash update threshold 10" this means that the flash update will be suppressed (Not Sent) if the next regular update is due in either 10 seconds or less.
See the change in the output after applying this command....
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds, next due in 23 seconds
Flash update is suppressed when next update due within 10 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
This is just to avoid multiple updates from happening...As the regular update is less than 10 seconds away no point in sending another flash update. The default value of a Flash update is 5 seconds.
Shelley
