show ip eigrp topology and topology all-links show different successor paths?

[gregoriusutama]

Hello,

Some time ago I got into a problem where R1 would like to communicate with the loopback interface of R2. R1 can reach R2 through RA and RB. EIGRP runs through the whole network. R1 was configured with `variance 10` and nothing else. The path through RB is expensive, due to the pre-configured high delay values. Let's say that the FD through RA is 1000, and the FD through RB is 3500 However:

1. R1 chooses path through RB even tho the FD and RD through RA is lower
2. There is only one path inserted in the routing table, the path through RB
3. The `show ip eigrp topology` command shows 1 successor, and FD is 3500
4. The `show ip eigrp topology all-links` command shows 1 successor, and FD is 1000, says the RA path is the chosen path, and it also shows RB as another path there, but not as successor even though the variance was 10
5. Let's just say the loopback interface of R2 is 172.16.0.1/32. Doing `show ip route 172.16.0.1` in R1 shows both routes through RA and RB, but RB is the chosen one (the one marked with star). There is a load balancing action shown tho, (I forgot the numbers, so let's just say the load balancing is RA:RB = 1:3).

How is this possible? I forgot other running configurations. I guess there may be some configurations that I missed. I want to know all possible configurations that may result in this situation.

Thank you in advance!

[gregoriusutama]

This seems to be a bug is it not? Because it does not come from actual Cisco device, this is from a sim. But I just want to know if this is possible in real Cisco device.

[paul driver]

Hello
Preemption of the feasible successor to successor isn’t applicable even though your feasible successor has the better optimal path it sounds like wasn’t calculated as that at time of convergence therefore eigrp chosen the RB link as the best path however if RBs path disappears RA would probably succeed given its reported metrics you have stated.

[gregoriusutama]

Alright I get what you said. But why is the output of `show ip eigrp topology` and `show ip eigrp topology all-links` show different successor routes? As I said before, the eigrp topology command shows the successor route is the RB (the worse route), but all-links says that the successor route is RA. This is the expected behavior, or no?

[paul driver]

Hello

Without see that topology table i cannot really comment but note the "all links" show all successors, including non and feasible ones.

[Georg Pauwen]

Hello,

which simulator are you using ? If possible, post all configurations as well as an overview of your topology, so we can lab this. It might as well indeed be a bug in your simulator...

[gregoriusutama]

Sorry but I don't have access to the sim again.

But as I remember correctly, the configuration under `router eigrp <as number>` is just `variance 10` and a couple of `network` commands.