ORACLE_HOSTNAME for existing database

Question

We did a fresh install of oracle 10.2.0.4 database. The database is up and running fine.
Recently we decided that we will use virtual hostname and so we configured a new ethernet card and IP address.
The problem is we set ORACLE_HOSTNAME to the virtual hostname in the environment variable and started the database. Still the database is using the old hostname.
SQL> select instance_name,host_name from v$instance;
INSTANCE_NAME HOST_NAME
PRODDB server01
SQL>
Added the IP address and the virtual hostname to the /etc/hosts file.
$export ORACLE_HOSTNAME=prodserver
Restarted the database.
SQL> select instance_name,host_name from v$instance;
INSTANCE_NAME HOST_NAME
PRODDB server01
SQL>
After the restart host_name is still the actual hostname
How to overcome this situation ?

Answer 1

I am referring to the [Oracle Document|http://download.oracle.com/docs/cd/B28359_01/install.111/b32002/pre_install.htm]
Which says
2.5.3 Installing on Multihomed Computers
You can install Oracle Database on a multihomed computer. A multihomed computer is associated with multiple IP addresses. This is typically achieved by having multiple network cards on the computer. Each IP address is associated with a host name. In addition, you can set up aliases for the host name. By default, Oracle Universal Installer uses the ORACLE_HOSTNAME environment variable setting to find the host name. If ORACLE_HOSTNAME is not set and you are installing on a computer that has multiple network cards, then Oracle Universal Installer determines the host name by using the first entry in the /etc/hosts file.
Clients must be able to access the computer either by using this host name or by using aliases for this host name. To verify this, ping the host name from the client computers using the short name (host name only) and the full name (host name and domain name). Both tests must be successful.