&tldr; in sqlnet.ora :
# the minimum allowed client version to connect to the databases from this home # set this to accept lower versions of the autentication protocol SQLNET.ALLOWED_LOGON_VERSION_SERVER=11 # if you have a database link to a lower version of an Oracle # set this to that lower version to talk the same authentication protocol # 12a => 12.1.0.2 # SQLNET.ALLOWED_LOGON_VERSION_CLIENT=12a # 12a for Oracle Database 12c release 12.1.0.2 or later # 12 for the critical patch updates CPUOct2012 and later Oracle Database 11g # 11 for Oracle Database 11g # 10 for Oracle Database 10g # 9 for Oracle9i # 8 for Oracle8i
Ah, an old client is trying to connect to Oracle 12c (presumably)… ;)
Also “ORA-03134: Connections to this server version are no longer supported” can occur.
This actually implies that the authentication protocols use between client and server do not match. In Oracle 12c, the authentication protocol uses SHA-2 encryption algorithm by default, where older clients use SHA-1. So when an older client is used with defaults, the server will not accept the connection.
The best option would be upgrading the client, but when older dll’s are used (like ojdbc14.jar and you can not change this), this is a problem. The database instance can be told to accept older clients and use the older SHA-1 encryption algorithm.