Hi Alex,
NPM does indeed use CDP as well as MAC address tables, ARP tables, and a bunch of other stuff to discover and calculate topology. The following things help make it more accurate:
- Add all of the involved network devices to NPM.
- Make sure topology polling is enabled on each node (list resources tells you).
- Enable CDP where possible.
- Verify SNMP credentials for your nodes are working.
Keep in mind that ConnectNow provides you with a representation of how two or more nodes connect directly to each other, even if there are intermediate device. In other words, if you have network path A -> B -> C but only have A and C on your map then hit Connect Now, it will draw a line between A and C. To discover the whole topology rather than logically connecting the nodes already in your map, you could use NTM.