Partly as a result of having problems with conflicting versions or bitness with the full installation of Oracle client, my development team (of which I'm a member) has been moving towards using Oracle Instant Client and avoiding the installation on our development machines for most new projects. This has worked out pretty well, even to the point that we deploy to production with this setup. Since we're mostly a .NET shop, we're using the native client (with .NET wrappers), rather than the Java one.

Now a client is requiring that we register the database service with an LDAP server and use the LDAP server for name look up. They have provided sqlnet.ora and ldap.ora files (and an accompanying encryption config file) that appear to be correct. In particular, the sqlnet.ora file does specify LDAP as a possible source for looking up net service names:


I am confident that the machine I'm working with can use LDAP to access the service since I was able to do so using SQL Developer (which allowed me to input the LDAP information directly). Assuming they are correct, how can I get Instant Client to recognize this configuration and use LDAP for the name look up?

What I've tried so far

I have tried setting the TNS_ADMIN environment variable to the directory that contains the provided files, and while this works fine for making Instant Client recognize a tnsnames.ora file, it doesn't seem to be enough to get it to start looking at LDAP. Here are the results (with paths, usernames, and passwords changed):

(The following commands happen to be Windows Command Prompt, but I imagine something similar is doable on Linux. The sqlplus seen here is the Instant version as well, with accompanying Instant Client binaries in the same directory.)

C:\TEMP>SET TNS_ADMIN=C:\path\to\sqlnet\ldap\and\tnsnames\ora\files



SQL*Plus: Release Production on Mon Jul 7 10:22:25 2014

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options

SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release - 64bit Produ
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options


SQL*Plus: Release Production on Mon Jul 7 10:24:21 2014

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

ORA-12154: TNS:could not resolve the connect identifier specified

Side note

Are there tags for TNS, LDAP, or Instant Client (or even just normal Oracle Client) that could be added to this question? I couldn't locate any.

  • Is it the correct executable? "where sqlplus" Jul 7, 2014 at 19:25
  • @BjarteBrandt Yes, it is the one I expect it to be when I run where (C:\TEMP\sqlplus.exe). To be more specific, sqlplus is not "installed" on the machine. It's just sitting in the current directory, with the client binaries beside it. It's definitely picking up on the tnsnames.ora file using the TNS_ADMIN environment variable, since that is off in a completely different directory.
    – jpmc26
    Jul 7, 2014 at 19:26
  • @BjarteBrandt To confirm it's using the right client binaries, I went ahead and ran where oci.dll, too. It also gives the expected result: C:\TEMP\oci.dll.
    – jpmc26
    Jul 7, 2014 at 19:30
  • could be a domain issue. Did you also try with FQ name? (dbname_or_whatever.domainname)
    – user953
    Jul 7, 2014 at 20:41
  • 2
    @ora-600 Sorry, I forgot about this question. It turned out to be problems with the config files themselves, which were provided to us by our client. (Possibly the Kerberos config file; I can't recall off-hand.) What's funny is that I was working in a dev environment trying to do this, it was equally problematic to get it working in staging, and it still isn't working in prod as far as I know. (We ended up using a local TNS name to get the app working.) Definitely wasted money for the project; even if/when it works in prod, the return on investment would be miniscule compared to the cost.
    – jpmc26
    Dec 22, 2014 at 16:55

2 Answers 2


Place the sqlnet.ora and ldap.ora files in your $ORACLE_ADMIN directory and make sure to set the environment variables. I made mine the TNS_ADMIN directory

(Linux) my .bashrc

export TNS_ADMIN=/opt/oracle/instantclient_12_1/network/admin

$ ls
ldap.ora  sqlnet.ora  tnsnames.ora

And I was able to connect to a DB not in my tnsnames.ora


Using an Oracle 19c instant client, I found it necessary to copy the OH/[network|/mesg]/oraus.ms[bg] files from a 19c server, to the same location in instant client.

The tns files were copied so that tnsping would work, and the ldap files so that LDAP resolution would work.

$ ls -l $(pwd)/{ldap,network}/mesg/*
-rw-r--r-- 1 oracle dba 136704 Jul 21 06:20 /opt/oracle/instantclient_19_16/ldap/mesg/ldapus.msb
-rw-r--r-- 1 oracle dba 185547 Jul 21 06:20 /opt/oracle/instantclient_19_16/ldap/mesg/ldapus.msg
-rw-r--r-- 1 oracle dba  50688 Jul 21 06:12 /opt/oracle/instantclient_19_16/network/mesg/tnsus.msb
-rw-r--r-- 1 oracle dba 259879 Jul 21 06:12 /opt/oracle/instantclient_19_16/network/mesg/tnsus.msg

$ tnsping js01

TNS Ping Utility for Linux: Version - Production on 21-JUL-2023 06:26:34

Copyright (c) 1997, 2021, Oracle.  All rights reserved.

Used parameter files:

Used LDAP adapter to resolve the alias
OK (0 msec)

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.