根据redis的说明，protected-mode在同时存在如下两种情况时触发：
1) The server is not binding explicitly to a set of addresses using the "bind" directive.
2) No password is configured.
当Redis服务器存在这两种情况时，客户端（非服务器本机）可以正常连。但是进行数据操作时报错：
(error) DENIED Redis is running in protected mode because protected mode is enabled, no bind address was specified, no authentication password is requested to clients.
Redis提供的解决方案：
1) Just disable protected mode sending the command 'CONFIG SET protected-mode no' from the loopback interface by connecting to Redis from the same host the server is running, however MAKE SURE Redis is not publicly accessible from internet if you do so. Use CONFIG REWRITE to make this change permanent.
2) Alternatively you can just disable the protected mode by editing the Redis configuration file, and setting the protected mode option to 'no', and then restarting the server.
3) If you started the server manually just for testing, restart it with the '--protected-mode no' option.
4) Setup a bind address or an authentication password. NOTE: You only need to do one of the above things in order for the server to start accepting connections from the outside.