# 连接失败，提示：exception: login failed 以及 U_STRINGPREP_PROHIBITED_ERROR
#### 问题描述
使用如下命令连接DDS实例时报错。
**./mongo "mongodb://rwuser:** *xxxxxx* **@192.168.0.45:8635,192.168.0.96:8635/test?authSource=admin\&replicaSet=replica"**
报错信息如下：
```
MongoDB shell version v4.0.3
connecting to: mongodb://192.168.0.45:8635,192.168.0.96:8635/test?authSource=admin&replicaSet=replica
2021-11-05T05:52:53.717+0000 I NETWORK  [js] Starting new replica set monitor for replica/192.168.0.45:8635,192.168.0.96:8635
2021-11-05T05:52:53.718+0000 I NETWORK  [ReplicaSetMonitor-TaskExecutor] Successfully connected to 192.168.0.45:8635 (1 connections now open to 192.168.0.45:8635 with a 5 second timeout)
2021-11-05T05:52:53.718+0000 I NETWORK  [js] Successfully connected to 192.168.0.96:8635 (1 connections now open to 192.168.0.96:8635 with a 5 second timeout)
Implicit session: session { "id" : UUID("5945d2a5-8275-4e3c-b06f-632f062a2ead") }
MongoDB server version: 4.0.3
2021-11-05T05:52:53.722+0000 I NETWORK  [js] Marking host 192.168.0.96:8635 as failed :: caused by :: Location50692: can't authenticate against replica set node 192.168.0.96:8635 :: caused by :: Error preflighting normalization: U_STRINGPREP_PROHIBITED_ERROR
2021-11-05T05:52:53.722+0000 I NETWORK  [js] Successfully connected to 192.168.0.45:8635 (1 connections now open to 192.168.0.45:8635 with a 0 second timeout)
2021-11-05T05:52:53.723+0000 I NETWORK  [js] Marking host 192.168.0.45:8635 as failed :: caused by :: Location50692: can't authenticate against replica set node 192.168.0.45:8635 :: caused by :: Error preflighting normalization: U_STRINGPREP_PROHIBITED_ERROR
2021-11-05T05:52:53.724+0000 I NETWORK  [js] Marking host 192.168.0.96:8635 as failed :: caused by :: Location50692: can't authenticate against replica set node 192.168.0.96:8635 :: caused by :: Error preflighting normalization: U_STRINGPREP_PROHIBITED_ERROR
2021-11-05T05:52:53.725+0000 I NETWORK  [js] Marking host 192.168.0.45:8635 as failed :: caused by :: Location50692: can't authenticate against replica set node 192.168.0.45:8635 :: caused by :: Error preflighting normalization: U_STRINGPREP_PROHIBITED_ERROR
2021-11-05T05:52:53.725+0000 E QUERY    [js] Error: can't authenticate against replica set node 192.168.0.45:8635 :: caused by :: Error preflighting normalization: U_STRINGPREP_PROHIBITED_ERROR :
DB.prototype._authOrThrow@src/mongo/shell/db.js:1685:20
@(auth):6:1
@(auth):1:2
exception: login failed
```
#### 可能原因
输入的实例密码异常。
#### 排查思路
- 检查设置的DDS实例密码中是否有'@'、'%'和'!'字符，如果有，需要转义。
- DDS实例当前支持的特殊字符，有（\~ ！@ # % \^ \* - _ = + ？，其中使用%@需要转义）。
 
#### 处理方法
方法一：修改DDS实例的密码，新密码中不能包含'@'、'%'和'!'字符。
方法二：连接DDS实例时，需要分别将'@'、'%'和'!'字符进行转义，替换为对应的十六进制的URL编码（ASCII码）"%40"、"%25"和"%21"。
例如：密码为\*\*\*\*@%\*\*\*!，对应的URL编码为\*\*\*\*%40%25\*\*\*%21。
#### 背景知识
'@'、'%'和'!'字符在DDS实例连接时会作为特殊的字符进行处理，如果设置的DDS实例中使用了上述字符，在使用高可用连接地址连接DDS实例时，需要对其进行转义处理，否则不能得到预期的解析。