title: What is the difference between "ORA-12571: TNS packet writer failure" and "ORA-03135: connection lost contact"?
body: <p>I am working in an environment where we get production issues from time to time related to Oracle connections.  We use ODP.NET from ASP.NET applications, and we suspect the firewall closes connections that have been in the connection pool too long.</p>
  
  <p>Sometimes we get an "ORA-12571: TNS packet writer failure" error, and sometimes we get "ORA-03135: connection lost contact."  </p>
  
  <p>I was wondering if someone has run into this and/or has an understanding of the difference between the 2 errors.</p>