Maximum EIGRP neighbors

[brian.carlson]

Is there a limit to the maximum number of EIGRP neighbors? I have a 7206VXR with 256MB of memory and am closing in on 1000 neighbors (800) and adding more every day. I've heard that 1000 is the magical number for EIGRP neighbors before there are issues.

[ruwhite]

The "normal" answer is: "It depends." :-) There isn't any "magical number" for the maximum number of EIGRP neighbors, it really depends on a couple of things:

-- How much information are you sending to each neighbor?

-- How much information are you getting from each neighbor?

-- What are your processor and link loads like?

So, for the first question, it's more than just the number of routes, it's also the number of queries your hub router needs to send you lose a link. Summarization and stubs both play a role here, with summarization decreasing the amount of information from the hub to the remotes in "normal operation," and stubs helping out when there's a topology change. Stubs mostly reduce the amount of processor required on the hub router, rather than really doing a lot for the remotes (this is something normally misunderstood about stubs, that it's for reducing load on the remote routers--summarization reduces load on the remotes, stubs on the hub).

The second question is the same one, but in the other direction. How many routes is each remote sending towards the hub? This has a huge impact on processing and work on the hub side, and is dirctly impacted by filtering, summarization, and marking the remotes stubs.

Now, the third question is mostly just looking at the link statuses, and how much hardware you throw at the problem.

Having said all of this, I would say that, in my experience, you've reaced the top level of where you want to go in terms of peers. 1000 isn't a "magic number," but it's the most I can recall seeing on any real, operational network. The primary problem you're going to hit isn't in bringing up more than this, it's in converging if you have to bring them all up at once, for some reason. Of course, if you're summarizing from the hub router(s) into the rest of the network, and following all the concepts above, you're going to be much better off than if you don't do them.

Again, 1000 neighbors isn't a "magic number." You're close to the maximum I've ever seen in the field, but that doesn't mean more aren't possible, it's just a matter of making certain it actually works in your environment.

HTH

:-)

Russ.W

[brian.carlson]

Hi Russ,

Thanks for the reply. As an aside, I was in a few of your Networkers sessions and wanted to say you did an excellent job, you have a great sense of humor. Anyway, we are summarizing our hub site routes down to 3 routes which are sent to the remote sites. Our remote sites typically will send 2 or 3 routes back to the hub site. So I think we have the summarizing part taken care of. We don't do any stub routing which we should/will probably implement soon. Other than that, I'm guessing that at this point (nearing 1000 neighbors) are options are limited. Is the best solution a second hub site router at this point? Static routes are obviously an option but that would require more configuration maintenance to add those everytime. Any suggestions? Thanks again.

[ruwhite]

Thanks for the networkers compliment! :-)

I would say the best option at this point would be a second hub site router, unless you want to start moving into something like statics. And I would definitely recommend using stubs....

:-)

Russ.W

[dgahm]

I have never seen a definitive max number. There are so many variables that would impact the load on router resources, that this is very much a "it depends" situation.

What does your processor and memory usage look like?

show processor

show processor cpu

show memory statistics

sh memory failures

Are most of these neighbors configured as stubs? If so that would help limit queries, and updates. Are you doing any route filtering/summarization? How big is the route table?

Have you done any failure mode testing to see if the router can handle it? A clear ip eigrp neighbors would be interesting -- during a maintenance window of course.