??add an entry in the hosts file :ORA-12545 Connect failed because target host or object does not exist

I track down the solution to ora-12545 error in MetaLink. what and where is the "OMS system hosts file" it refers to??

thanks

Fact: Oracle Enterprise Manager

Symptom: Connecting to Database from Enterprise Manager Console Fails Symptom: Connecting to Database outside Enterprise Manager Console succeeds
Symptom: ORA-12545 Connect failed because target host or object does not exist

Cause: There are two frequent causes of this problem:

o 'Host1' and 'host2' are the same and the OMS is on a different system

   than the OEM Client. The cause is simply a TCP/IP configuration issue

   in that this hostname does not resolve to the IP address on the OMS system.

o 'Host1' and 'host2' are different. The OMS may be running on the same

   or a different system than the OEM Client. The reason why 'host1' is

   different than 'host2' could be that the real hostname of the node on

   which the managed database resides is 'host1', while the node is generally

   known across the network as 'host2'.

When the OEM Console performs service discovery, it contacts the Intelligent
Agent running on the node that is being discovered. The Agent registers
the node with OMS using the real hostname that it gets from running the
'hostname' command.

To verify if this is the case, run the 'hostname' command on the node of the
managed database. If the result is 'host1', then this is the cause of the
difference between 'host1' and 'host2'.

Fix:
1. Find the sqlnet.log file on the system on which the Oracle Management

    Server is running and in the Oracle Home in which it is installed.

2. Check at the end of the sqlnet.log for an entry for the ORA-12545 error.

    In particular, check the description of the address it is trying to

    connect to. Note down the value of the HOST parameter, e.g.,
'host1'.

3. Ping this hostname from the system on which the OMS is running. You

    should find that ping fails with a message such as 'Bad IP Address'.

    For example:

      OMS system:
      ping host1
      Bad IP Address host1

4. Find the tnsnames.ora file on the system on which the Oracle Enterprise

    Manager client is installed and in the Oracle Home in which it is     installed.

5. Get the Net8 service name for the managed database and note down the

    value of the HOST parameter, e.g., 'host2'. You may find that this value

    is different from the value found in the sqlnet.log file above.

6. Ping this new value for host. This time you should find that the ping

    command succeeds. For example:

      OEM Client system:
      ping host2
      Pinging host2 [178.4.5.1] with 32 bytes of data:
      Reply from 178.4.5.1: bytes=32 time=30ms TTL=253
      ...

7. The solution is to add an entry in the hosts file of the system on which

    the Oracle Management Server is running so that the hostname
'host1' on

    the OMS systems resolves to the same IP address as 'host2' on the OEM
    Client system. For example:

      OMS system hosts file:
      host1       178.4.5.1

      OMS system:
      ping host1
      Pinging host1 [178.4.5.1] with 32 bytes of data:
      Reply from 178.4.5.1: bytes=32 time=30ms TTL=253
      ...

After this modification and test, you should find that you can now connect
to the managed database from the Enterprise Manager Console. Received on Fri Nov 02 2001 - 11:26:48 CST