[sophacles]

Running out of ports is a poor way to put it, but it can be read as "Run the target machine out of fd (file descriptors)." In unixy systems there is a system parameter limiting the maximum number of file descriptors that can be open at one time (actually 2, per-proces and system-wide limits). These limits need to be turned up for big servers.

The why is a pretty boring story: the number exists as a check against runaway processes or big jobs (e.g. busy servers) causing an I/O overload, so the numbers are set to a "reasonable value" by default. Of course the reasonable value is usually much lower than the system can handle, and at tuned for older common hardware.