RIP timers

A RIP timer is a network protocol mechanisms that

  • regulates RIP performance through timed intervals for routing updates and route management

  • controls when routes are marked invalid, placed in holddown, or flushed from the routing table, and

  • helps prevent network congestion by managing the timing of routing updates across devices.

RIP timer stages

RIP uses numerous timers to regulate its performance. These are the timer stages for RIP:

  • Update—The routing-update timer is the interval between periodic routing updates. This is how often the device sends routing updates. Generally, set to 30 seconds, a small random delay added to prevent simultaneous route updates.

  • Invalid—Each routing table entry has a route-timeout timer for the last valid update. When this timer expires, the route is marked invalid and moves to holddown once the timer expires. The default is 180 seconds (3 minutes).

  • Holddown—The period the system waits before accepting any new updates for invalid routes. The default is 180 seconds (3 minutes).

  • Flush—The route-flush timer marks the period from when the system receives the last valid update until the route is discarded and removed from the routing table. The default is 240 seconds (4 minutes).

RIP timer sequence when adjacent router interface goes down

When an adjacent router goes down, routing updates stop, and the Invalid and Flush timers start increasing. In the first 180 seconds, nothing will happen. After 180 seconds, the Invalid timer expires, marks the route invalid, and the Holddown timer begins, holding the route for 60 seconds. If there is no routing update for the adjacent router;s status (that is, it is still down), then the route enters into the Flush state where in total the system has waited for 240 seconds from the last update (180 seconds for the Invalid timer and 60 seconds for Holddown timer), and the system flushes the route. Even if the adjacent routers interface comes up immediately, the system waits for the Holddown timer to complete the 120-second period before accepting updates.