RTFM first ! There is no (Debian) packages for 'ipdiscover' !!
In documentation, you have to understand there is 'ipdiscover' for agents and 'ipdiscover' for the server.
With agents, you have to activate ipdiscover, define each subnets you want, define 1 (or 2) agents for each subnets defined. Wait a day and you have ipdiscovered subnets.