EIGRP acting funny (Neighborship but no routes, FD Inaccessable)

[Dean Romanelli]

Hi All,

I am witnessing a very puzzling issue at work this morning on my EIGRP network, and I'm hoping someone can provide some answers:

I have multiple sites world-wide, and one of my sites is causing an issue:  My other sites do not see the EIGRP route for this particular site, but they do see the neighborship.   When I show the EIGRP topology table for the subnet (we'll say its 1.1.1.0/27, for example's sake), is says "FD Inaccessible."  There is no redistribution happening on this segment, it is pure EIGRP to the destination.

So, we changed the site addressing space from 1.1.1.0/27, to 1.1.3.0/27 (again, for example's sake), and everything can now see the site that was causing the issue, and all is happy.  This lead me to believe the original IP space was in conflict, and existed elsewhere on the network, but I don't believe this is the case due to the following:

1. If the space existed elsewhere, then the devices holding those addresses should have become visable on the network once I changed the addressing to something "unique," and they didn't. I have no record of the space existing elsewhere.

2. It's been in production for more than a year under this subnet without issue.

Anyone have any ideas?

[juan-ruiz]

Hi Romanelli,

Not know much about the configuration do you have no summary configured on your EIGRP configuration?

Thanks,

Juan

[Dean Romanelli]

Hi Juan,

Thanks for replying.  Yes, I have "no auto-summary" configured under the EIGRP configurations.

I would paste config outputs if I could, but unfortauntely I can't really share company info to that degree.

Dean

[juan-ruiz]

Hi Dean,

I totally understand.

Do you have another routing source in your network that is new and might have a better admin distance than EIGRP that might be using that network and it overlapped?

[Dean Romanelli]

Juan,

No, unfortunately. We only use EIGRP on this segment.  I had suspected that it was an IP conflict as well, but when I removed the subnet, nothing else on the network became visible, which I had thought it would, since it was no longer being "bogged-down" by any conflicts.

[juan-ruiz]

For the site that sees the neighbor up but not the route in the routing table what does the topology table show for this neighbor?

If you are using EIGRP on this segment only how does the routing reach the central site? Does it use another protocol and redistribution?

I’m just throwing ideas out there that maybe you can explore or have already.

is this site firewalled by any chance?

[Dean Romanelli]

Hi Juan,

When the site was configured for the old space that was causing the issue, the topology table said "FD Inaccessible."

The Central site uses EIGRP. No redistribution occurring.  The central site is firewalled, but we've already ruled that out.

I think the only feasible answer here is that there is a conflict somewhere, even though we have no record of the space existing elsewhere, and cannot reach it.

[juan-ruiz]

Hi Dean,

Let me know if you ever find out what is the root cause and if you are planning on testing and debugging to gather more info.

I hope it works out.