RIPng uses the following timers:
Update timer: This timer periodically triggers Update packet transmission. By default, the interval at which Update packets are sent is 30s. This timer is used to synchronize RIPng routes on the network.
Age timer: If a RIPng device does not receive any Update packet from its neighbor before a route expires, the RIPng device considers the route to its neighbor unreachable.
Garbage-collect timer: If no packet is received to update an unreachable route after the Age timer expires, this route is deleted from the RIPng routing table.
Hold-down timer: If a RIP device receives an updated route with cost 16 from a neighbor, the route enters the holddown state, and the hold-down timer is started.
The following describes the relationship among these timers:
The advertisement of RIPng routing updates is periodically triggered by the update timer with default value 30 seconds. Each routing entry is associated with two timers: the Age timer and garbage-collect timer. Each time a route is learned and added to the routing table, the Age timer is started. If no Update packet is received from the neighbor within 180 seconds, the metric of the route is set to 16, and the garbage-collect timer is started. If no Update packet is received within 120 seconds, the route is deleted after the garbage-collect timer expires.
By default, hold-down timer is disabled. If you configure a hold-down timer, it starts after the system receives a route with a cost greater than 16 from its neighbor.