Listing of hosts in a LAN or domain name group?

What’s the preferred ruby way of listing hosts in a LAN or within a
domain group?

In particular, I am interested in 4 things:

  • Listing all connected hosts in a LAN / domain group (assuming
    there could be some hosts
    that appear and disappear, like wifi hosts – ie. not just /etc/
    hosts ).
  • Listing all hosts with a particular condition (say, allowing
    authenticated ssh connections).
  • Avoiding any hosts that are not in a trusted group (say,
  • Doing it fast.

I’m interested in Linux, mainly, but if the solution is multiplatform,
the better.