RIP flush time

By default RIP sends updates each 30 seconds

In this lab we change the value of the invalid timer to 90 seconds

What happens if we filter RIP updates R2 sends over fa0/0 link?

Before the filter

Because R1 receives no updates about on path fa0/0, the path is invalidated after the invalid timer

Let’s do the same thing of the other path (the last)

Because the last path to the has been lost, the route in the routing table is marked as being inaccessible and enter the holddown state

Which expires in 180 seconds

In RIP database the route is marked as possibly down,

as soon as the route enters the holddown state

Are updates accepted during holddown? We send an update during holddown and check that the udpate is not accepted as the holddown counter keep counting down

When flush timer enters into play? Let’s configure the holddown timer to be equal to 300 seconds to a period that is larger than the flush time which is by default 240 seconds

The route is flushed after 240 seconds

As soon as an update is received the timers (for the last path): flush and invalid timers are initiated to 240 and 90 seconds respectively

If no update is received for the invalid timer, the route (last path) is put into the holddown state for the duration of the holddown timer

If the invalid+holddown total time is lower than the flush time then the route disappears from the routing table before the flush timer expiration?!

Let’s confirm this hypothesis by recording the time of the next update and applying the distribute-list to stop udpates

After invalid “path” time the route is put into holddown state

After 240 seconds the route is deleted

Let’s now change the holddown timer to a value less so that invalid+holddown time is less than the flush time

We record the time of the last update before applying the distribute-list

After 90 seconds the route enter the holddown state (lost the last path to destination subnet)

After only 30 seconds the route is NOT deleted

But the counter is put to 0

Would it be able to be updated in this state? We suppress the filter so that update flow again…

And yes, as soon as an update is received the route came out of the holddown state (that has expired)

It has not to wait to be flushed before being installed again in the routing table…


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