mongo只读账户一直连接不上，WHY?

• 只读账户连接，一直连接不上。

[2016-08-28 12:15:49.094] [INFO] Mongodb - start initing.
[2016-08-28 12:15:49.096] [INFO] Mongodb - trying to connect db#db [mongodb://read_all:pwd@ip:27017/db] 

• 正常账户连接，没有问题。

[2016-08-28 12:18:39.763] [INFO] Mongodb - start initing.
[2016-08-28 12:18:39.764] [INFO] Mongodb - trying to connect db#db [mongodb://user:pwd@ip:27017/db]
[2016-08-28 12:18:40.212] [INFO] Mongodb - db#db [mongodb://user:pwd@ip:27017/db] ready.

有没有大神给点意见或者解决办法