ORA-12170: TNS:Connect timeout occurred

Time need for a client to make connection with the Database Server and authenticate it.
If client failed to establish and authenticate the connection in given time then database terminate the connection.
Value specified in this parameter is millisec (ms), sec or min. Default value is 60 seconds.

Get the following errors:
ORA-12170: TNS:Connect timeout occurred
ORA-12547: TNS:lost contact
ORA-12637: Packet receive failed

Oracle recommends to set parameter of listener and sqlnet.ora file both
In listener file: INBOUND_CONNECT_TIMEOUT_listener_name parameter
In SQLNET file: SQLNET.INBOUND_CONNECT_TIMEOUT parameter

Note: Value for INBOUND_CONNECT_TIMEOUT_listener_name parameter is set lower than SQLNET.INBOUND_CONNECT_TIMEOUT parameter.

Example

SQLNET.INBOUND_CONNECT_TIMEOUT=60

Note: if you do not specified the ms, sec or min then it will pick default as seconds.