RIP maximum equal cost paths feature

In this lab, we check how maximum equal paths feature works in RIP

In this lab R2 advertises subnetwork to R1 via RIP. R1 processed three equal paths through interfaces fa0/0, fa1/0 and fa1/1 to join R2 loopback0 interface subnet.

First, R1 uses R2 updates to populates RIP database

Because RIP is configured to accept four equal cost paths by default, it accepts the three of them

R1 default routing table is populated after

The protocol is router R1 is configured by default

To see the timers into run, we change their default values

At T0 we change the maximum accepted equalt cost paths from 4 to only 2 and observe the effect on tables : rip database, default routing table and cef

We notice that in RIP database, the third path has disapeared after 90 seconds the invalid timer

We redo our test and check how default routing table react

Using debug ip routing

In this Cisco router, as soon as the feature is configured the route (including the paths) are deleted waiting for the next updates to rebuild the entry again

Let’s redo the same test and check what happen on the wire at the control plane

On the path (fa1/0) that was deleted from the routing table (because of the maximum paths limit) R1 sends an update that includes the subnetwork

If the route (via path fa1/0) was in the routing table the split horizon rule would’ve prevented it from being advertised back to the advertiser (R2).

Because the split horizon check is done against the routing table, the is sent back to R2.

In R2 the route is not installed because of the connected subnet having the lowest admin distance.


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