Database Software

gurus:

I installed a 11.2.0.2 standalone grid infrastructure on a linux box and created a database manually. I then used netca to create my listener which created 2 listener files:

a. under my DB home:
aml6:/u00/app/oracle/product/11.2.0/dbhome_1/network/admin > cat listener.ora
# listener.ora Network Configuration File: /u00/app/oracle/product/11.2.0/dbhome_1/network/admin/listener.ora
# Generated by Oracle configuration tools.

LISTENER_ETL =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = aml6.lynk.lynksystems.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
)
)

ADR_BASE_LISTENER_ETL = /u00/app/oracle

b. under my grid home:
aml6:/u00/app/11.2.0/grid/network/admin > cat listener.ora
LISTENER_ETL=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_ETL)))) # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_ETL=ON # line added by Agent

I observed that the one under my DB home was the one that really got used when I tried to logon to a database.

Here are my questions:
1. what is the use for the listener under my DB home?
2. what is the use for the listener under my grid home?
3. the grid infrastructure document says that the default home for listener and tnsnames files are grid home, however, it seemed that I have to use the listener under my db home directory.
4. which listener is the ASM instance use?

Thanks a lot for your help.

dz