测试环境安装了一套Oracle 12c R2的数据库，想要通过PL/SQL developer连接上数据库，但是报错
ORA-28040: No matching authentication protocol
上网查了原因：Oracle 12c的参数SQLNET.ALLOWED_LOGON_VERSION默认等于11。当我们使用11g JDBC之前版本的thin驱动连接的时候，就会报错。
于是按网上的方法解决方法来做：
在数据库服务器上的oracle/network/admin/sqlnet.ora文件添加一行SQLNET.ALLOWED_LOGON_VERSION=8
修改之后再次连接却又报错ORA-01017: invalid username/password; logon denied
确认用户名和密码是没问题的，但就是连接不上，在服务器端就可以连接
[oracle@t13s ~]$ sqlplus pdbadmin@pdb1
SQL*Plus: Release 12.2.0.1.0 Production on Fri Mar 17 10:25:22 2017
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Enter password:
Last Successful login time: Thu Mar 16 2017 20:28:26 +08:00
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
PDBADMIN@pdb1>
于是在MOS上搜索相关文档，查到这样一篇文章Client / Server Interoperability Support Matrix for Different Oracle Versions (文档 ID 207303.1)
从文章中可以看出只有11.2.0.3及以上的版本的客户端才能连接12.2版本的服务端。再检查本地的Oracle客户端的版本是11.2.0.1，原来是客户端版本太低了，安装12.1版本的客户端，顺利登录。
MOS文章大致内容如下：
ClientVersion Server Version
12.2.0 12.1.0 11.2.0 11.1.0 10.2.0 10.1.0 9.2.0
12.2.0 Yes Yes Yes No No
12.1.0 Yes Yes Yes Was
11.2.0 Yes Yes Yes Was No
11.1.0 No Was Was Was
10.2.0 No MDS Was
10.1.0 No No Was Was Was
9.2.0 No No Was Was
Key:
ES Supported but fixes only possible for customers with .
LES or MDS Supported but fixes only possible for customer with a valid Limited Extended Support or Market-Driven Support contract respectively.
Was Was a supported combination but one of the releases is no longer covered by any of Premier Support, Primary Error Correct support, Extended Support, nor Extended Maintenance Support. Fixes are no longer possible.
No Has never been Supported
Specific Notes: