LMS 3.2 Device Discovery

dcioffi · ‎01-28-2010

Is there a document that gives a better technical explanation of the discovery process? The

documentation I've found so far is fairly superficial.

I'm testing discovery with a new LMS 3.2 installation and so far it seems like I will have to enter every IP subnet we have in a ping sweep, because devices just aren't getting discovered. I tried CDP alone with one seed - a router at the hub of our network. I tried discovery with that one seed router with both CDP and Routing Table - I would expect that to discover other devices via the subnets in the routing table. That's not what happened, so I'm wondering how the "Routing Table" module actually works.

If we don't have CDP everywhere, will devices without CDP be discovered?

Finally, I've seen a number of comments here that say not to use the DCR as a seed file. I must be missing something, because I would think that you'd want to do a discovery starting with what you already have to find out what's been added to it, without having to tell the app where to look. That seems to defeat the purpose of discovery.

Any assistance would be greatly appreciated!

Joe Clarke · ‎01-29-2010

Discovery requires that every device be reachable via SNMP using the SNMP credentials you configured in Discovery. Devices which are found by the various algorithms which are not reachable via SNMP will be marked as unreachable, and will not be added to DCR. So, while you may configure ping sweeps, and Discovery may be able to ping certain nodes, it does not mean that those nodes will be discovered.

Generally, users choose CDP and ping sweep. Routing Table is fine, but it can lead to SNMP CPU spikes on routers with large routing tables. The way the routing table module works is to poll the ipRouteTable via SNMP, then go through each ipRouteNextHop to find the next hops. Because polling this table can be CPU-intensive, it is often filtered out using an SNMP view.

If you only go with CDP, then devices which do not have CDP neighbors will not be found dynamically. Such devices would need to be manually added as seeds.

And I generally recommend people enable "Use DCR as seed". This can greatly cut down discovery time.