ORA-03135: connection lost contact - oracle

Question

I am getting the error as 'ORA-03135: connection lost contact' from my C# code while making connection to oracle DB. The same job works just fine from our test server. But it failed with ORA-03135: connection lost contact error from prod server.
The C# code use ODAC to connect to oracle DB.
Appreciate your inputs.
Thank you

Answer 1

This error is most likely caused by a firewall blocking the connection request. Check for any firewalls in your network or on the database server and make sure your access rules are configured correctly.
Also check this link for more troubleshooting tips: http://www.dba-oracle.com/t_ora_03135_connection_lost_contact.htm
ORA-03135: connection lost contact tips
What can I do to avoid the ORA-03135 error?
Answer: The oerr utility shows this for the ORA-03135 error:
ORA-03135: connection lost contact
Cause:
1) Server unexpectedly terminated or was forced to terminate.
2) Server timed out the connection.
Action:
1) Check if the server session was terminated.
2) Check if the timeout parameters are set properly in
sqlnet.ora.
The ORA-03135 error is common when connecting remotely when a firewall
terminates the connection.
One solution for the ORA-03135 error is to increase the value of the
sqlnet.ora expire_time parameter in the sqlnet.ora file or to check
for a expire parameter in a SQL*Plus profile.
To diagnose the ORA-03135 error, start by checking to see if the OS
PID still exists, using the "ps -ef | grep" syntax.
Check to see if there is a Network Address Translation (NAT) between
the client and server
In Windows, check to see if a Windows firewall is checking for your
local connections.
...
Also, setting the parameters sqlnet.inbound_connect_timeout and
inbound_connect_timeout_listenername to 0 can stop the ORA-03135
error.