Take a look into TIME-WAIT (sometimes spelled like TIME_WAIT by netstat utility) TCP/IP state:
Net effect of how TCP/IP protocol works is that one client can generate about 500 database connections per second and then it [client] will hit OS limit. The number 500 comes from 30K ports available / 60 TIME-WAIT seconds.
Who would do that in the database world you may ask. Answer: if it can be done it will be done. I personally came across 3 applications in the last month doing exactly that, one finally hit the 30K connections limit in TIME-WAIT state.
Truth be told those were MySQL applications. MySQL is pretty forgiving when it comes to 500 connects/disconnects per second, but a) MySQL is Oracle now b) not a big deal to do the same on Oracle RDBMS either.
Btw, sometimes the situation can be both masked (and saved) by forcing local connections which bypass the TCP/IP stack. In that case all works fine till some part of application starts using TCP/IP.