To help users, I would like my code to discover Oracle databases on the LAN. I thought to do this by first detecting all hosts, then checking each host to see if it is listening on Oracle's default port.
Any ideas how to go about this? Preferably in Java, but any language or algorithm would do.
Are you using DHCP? If so, your DHCP server has a list of the leases it has passed out. That should do you for a list of hosts on the LAN. Then try opening a connection to the Oracle port on each of those hosts and see if it accepts the connection.
It should be pretty simple to implement as a shell script with half a dozen lines or so. Java seems like overkill for something like this. Loop through the leases file, grab the IP from each lease, and telnet to the Oracle port; if it connects, disconnect and print the IP to standard out.