Slow connection to Oracle

   About two years ago I was investigating a request from DEV team about slow connection to the database. The problem looked strange for me since we had two databases in one RAC and one had a version 10.2.0.4 and the other one was 11.1.0.7. The issue with slow connection was only for 11.1.0.7 database.
After long digging I found that one of two DNS servers in /etc/resolv.conf was unreachable. I had commented the bad DNS and the issue with slow connection has gone.
   Two months later the same problem was reported on the support.oracle.com like a bug that fixed in version 11.2.0.2. Note ID 561429.1.

So if you experiencing the same problem then just do the same!