Oracle 12c R2 on Windows Server added more complexity than even 12c R1.
1) Windows user name cannot have a space in it. The Oracle Setup will hang up before it completes (with no explanation).
2) Turn off Password Complexity on Windows Server or Oracle Setup can't create a user for Oracle (if you are wanting it to create a user)
3) In listener.ora and tnsname.ora, change "localhost" to your machine name or you will not be able to connect from other machines.
4) If you need older clients to connect with Oracle 12c R2, in the sqlnet.ora, you will have to add:
SQLNET.ALLOWED_LOGON_VERSION_SERVER=8
SQLNET.ALLOWED_LOGON_VERSION_CLIENT=8
You can use a different minimum (instead of 8), but this is the lowest.
You will get this error on other machine if this is the case:
ORA 28040: No matching authentication protocol
5) If you have already created users in Oracle before adding the entries to sqlnet.ora, you will have to reset the passwords if you want to connect from the older versions.
ALTER USERIDENTIFIED BY
You will get the following error until this is done (for no apparent reason):
ORA-01017 Invalid Username/Password
Resources:
https://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:9533918300346989898
https://community.microstrategy.com/s/article/ORA-28040-No-matching-authentication-protocol-when-connecting-to-Oracle-12c-or-higher-database
https://stackoverflow.com/questions/37615088/unable-to-connect-to-oracle-12c-from-client-machine
