EIGRP feasible successor

[bellocarico]

Please check the attachment.

Can anybody explain me why R2 and R3 are not the each other feasible successor to N1 (192.168.1.x)?

Thanks to read!

[bellocarico]

Here is the attachment :-)

[pkhatri]

Hi,

You have to remember that the reported distance by a router has to be less than the feasible distance for that route for it to be considered a feasible successor.

In your case, the FD is 40537600 but the reported distance (RD) by R3 (when considering R2) is also 40537600. Since the RD is equal to the FD (but not less than the FD), it is considered to not be a feasible successor. The same applies for the route advertised by R2 to R3.

Hope that helps - pls do remember to rate the post if it does.

Paresh

[bellocarico]

I don't know why, but I was thinking it was less or equal, where of course it is not. Never mind...

Following the scenario, R2 and R3 will never become the each other feasible successor to N1

The only things I can think is to manually make one router preferred (modifying the delay between R1-R3 e.g. so R2 can use R3 as feasible.

However doing this way R3 still need to go active in case of R1-R3 link failure

Any better advice?

[pkhatri]

You can certainly introduce a delay using an offset-list so either R2 will use R3 as a feasible successor OR R3 will use R2 as a feasible successor. However, there is no way to make them both use each other as feasible successors. If one is the FS for the other, then the other cannot be the FS for the first one - that is once again as per the definition of feasible successor. You will have to live with one of the routers going active when the main link fails.

Pls do remember to rate posts that help...

Paresh