oracle dbguard配置监听insufficient privileges

从库在启动到nomount后，通过监听怎么也登录不上，报错

ORA-01031: insufficient privileges

Enter user-name:

经过多方查找资料最后在 tnsnames后面加上一行 UR=A就可以了，虽然不明白是怎么回事，以后再慢慢研究

ORCLSTD =

  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST =192.168.1.203)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl)
      (UR=A)
    )
  )