Understanding Timers in Routing Information Protocol

Understanding Timers in Routing Information Protocol

In this article I will explain you how is the packets transferred between routers in same broadcast domain is measured – Timers! Understanding timers in routing information protocol.

There are 4 types of timers available in RIP. Update, Invalid, Hold and Flush.

Update, Invalid and Flush timers all of them starts simultaneously at ZERO.

Update Timer: Default value is of 30 secs, it resets itself as soon as the update is received from neighboring router. Complete routing table is shared in this update.

However, any change in network topology will be shared immediately via triggered update.

Invalid Timer: Default value is of 180 secs, If a router fails to receive an update post 30 secs, it will wait for another 150 secs before declaring the route for which update was not received as “Invalid”

As soon as the route is marked Invalid a triggered update is sent to all the downstream routers with metric value 16 however, this route is still present in this router and will continue with hold timer of 60 secs before it flush outs the route from its routing table.

Hold Timer: It triggers as soon as Invalid timer is finished at 180 Secs. Hold timer will hold the Invalid route until the flush timer is complete on source router.

Flush Timer: Default time of 240 Seconds. This timer starts along with update and Invalid timer and it indicates how long a route can remain in a routing table before being flushed.

Imp: Router will not accept the route for which timer went into hold state. Instead it will flush the routes as soon as 240 secs are lapsed. Technically Hold timer starts when Invalid timer ends and ends with flush timer. Hence, hold timer is of just 60 secs.

Correction: Hold timer is of 180 Secs however, it only gets executed for 60 secs as show in the picture above.

Do you know these timers can be manipulated. I will explain you in next article. Stay tuned!

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