tnsnames.ora中的一个连接串不能从LISTENER连接时通过另一个监听连接（failover）

LISTENER.ORA文件内容：

LISTENER=
  (DESCRIPTION=
    (ADDRESS_LIST=
      (ADDRESS=(PROTOCOL=tcp)(HOST=hostname)(PORT=1521))
      (ADDRESS=(PROTOCOL=ipc)(KEY=extproc))))
LSNR2=
  (DESCRIPTION=
    (ADDRESS_LIST=
      (ADDRESS=(PROTOCOL=tcp)(HOST=hostname)(PORT=1526))
      (ADDRESS=(PROTOCOL=ipc)(KEY=extproc1))))
SID_LIST_LISTENER=
  (SID_LIST=
    (SID_DESC=
      (GLOBAL_DBNAME=CSDB)
      (ORACLE_HOME=/u01/app/oracle/product/10.2.0/db_1)
      (SID_NAME=CSDB))
    (SID_DESC=
      (SID_NAME=plsextproc)
      (ORACLE_HOME=/u01/app/oracle/product/10.2.0/db_1)
      (PROGRAM=extproc)))

tnsnames.ora文件内容

LSNR2=

      (ADDRESS=(PROTOCOL=tcp)(HOST=hostname)(PORT=1526))

CSDB=

  (description =

     (address = (protocol = tcp)(host = hostname)(port = 1521))

     (connect_data =

   (server = DEDICATED)

   (service_name = CSDB)

   )

   )

CSDB_SF=

  (description =

     (FAILOVER=on)

     (address = (protocol = tcp)(host = hostname)(port = 1521))

     (address = (protocol = tcp)(host = hostname)(port = 1526))

     (connect_data =

    (server = DEDICATED)

    (service_name = PROD)

    )

    )