Updated February 22, 2017
This is to guide NTM users with large networks regarding its performance during the discovery process. This also explains how the NTM discovery engine works and what goes on behind the scenes before displaying the network diagram.
All NTM versions
NTM includes a sophisticated multi-level discovery engine, which uses a combination of protocols and goes through 3 distinct phases in order to discover every node on a network and to produce a highly accurate map.
The completion of these 3 phases of the discovery process can be slowed down by a number of factors. Primarily these:
With all of that in mind, we have compiled the following recommendations to help you improve the performance of NTM as it discovers devices on your network.
The tendency of most NTM users is to try discovering their entire network on the first scan. The drawback here is, if you have a network with more than 1200 nodes you are in for a long wait and at the end of it, the map might look very cluttered. The smaller the range you define to scan, the faster you will receive the results and the easier it will be to interpret them. We recommend discovering Class C networks in at least 2 separate scans.
The most commonly used credentials should be at the top of the list, be it SNMP, WMI or VMWare. Performing this simple activity will help enhance the discovery. Also, note that the more credentials there are the longer discovery will take so do not use any unnecessary credentials.
Zero Hop Discovery
As you work your way through the discovery wizard, you will notice that you are prompted to provide the number of hops you wish to use during the scan. We recommend using 0 hops unless you are not finding all of your expected devices. The more hops the scan goes through, the longer it takes and 0 usually gets them all.
Scanning with NTM from within the same Management VLAN of your network can improve the speed of the discovery process significantly. This will reduce polling timeouts compared to scanning over VPN, dial-up or routing through another network.
If you manage a very large network or you see your network growing in the coming months, it would be best to run the discovery process during evening hours or on weekends and have your map ready for Monday morning. The key to this is making sure you have entered the proper credentials into the discovery wizard. Make sure to test your credentials before beginning the discovery process and leaving the building.