EIGRP Week: Wednesday

Welcome to wednesday, yesterday we configured EIGRP on a 5 router topology. Today we will take a closer look on how why EIGRP selects the paths through the network, and what happens if something or someone changes the topology. Lets take a look again at our network diagram, for a better understanding I marked the FastEthernet links green and the 10mbit Ethernet links are yellow.

Since EIGRP always chooses the fastest path as a succsessor R5s way to reach R1s loopback interface should go via R2 and the path via R3 should be in the EIGRP topology table as the feasible succsessor.

Lets check out the path packets are taking from R5 to R1s loopback interface:

As you can see packets are beeing routed via the 192.158.4.2 neighbor which is the 100 mbit highway to Loopback 0.

Now what about the topology table?

Our actual best path to the destination network is marked with the green arrow whilst the feasible succsessor is behind the yellow arrow.

Now lets see what happens if we take R2 out of the game.

R2 is gone and R3 has become the succsessor an also is beeing put in the routingtable with no delay. If R2 comes back online EIGRP changes the topology table as soon as the neighbor adjacency is beeing formed again and the old succsessor route will be reinstalled.

Thats all for this wednesday, tomorrow we wil look into EIGRP route manipulation.

The GNS3 file used for this is the same as provided yesterday and can be downloaded ->here<-
and the imagefile used is C3660-jk.bin