Managing Users  «Prev  Next»

Lesson 8Testing client connectivity
ObjectiveApply Oracle Net troubleshooting techniques.

Testing Oracle Client Connectivity

Oracle's TNS (Transparent Network Substrate) names resolution method relies on a configuration file known as tnsnames.ora. This file, typically located in the
, directory provides the necessary details for connecting to Oracle databases across a network. However, if you encounter issues connecting to an Oracle database, the tnsnames.ora file could be one of the potential causes. Here are several troubleshooting techniques you can utilize to resolve errors in this file:
  1. Syntax Verification: The tnsnames.ora file follows a specific syntax. 1) Misplaced parentheses, 2) missing parameters, or 3) typos can prevent the file from working correctly. Use a text editor to open the file and carefully verify the syntax against Oracle's official documentation. It is a common practice to verify the correct format using a working tnsnames.ora file from another system.
  2. Correct Naming: Confirm the naming conventions used in your tnsnames.ora file match those expected by your Oracle clients. This includes both the names of the databases and the names of the connection parameters.
  3. Location of the File: Ensure the tnsnames.ora file is in the correct directory. The default location is $ORACLE_HOME/network/admin, but this can be changed by setting the TNS_ADMIN environment variable to point to a different directory. Check the TNS_ADMIN variable and ensure it points to the correct directory containing your tnsnames.ora file.
  4. Permission Issues: Verify that the Oracle client has the necessary permissions to read the tnsnames.ora file. The file must have read permissions for the user running the Oracle client software.
  5. Connect Descriptor: Make sure the connect descriptor in the tnsnames.ora file contains valid hostnames or IP addresses, and that the port number matches the listener port on the database server.
  6. Testing Connection: Use Oracle's tnsping utility to test whether the Oracle client can connect to the database using the entries in the tnsnames.ora file. This utility helps you determine if the tnsnames.ora file is functioning correctly.
  7. Oracle Net Manager: Use the Oracle Net Manager (a GUI tool) to validate the tnsnames.ora file. It helps in managing and enabling detailed tracing for the client and the listener.

Remember, if you make any changes to the tnsnames.ora file, you should always attempt a new connection afterwards to ensure the changes have taken effect. Oracle's TNS resolution does not require a server or service restart after modifying the tnsnames.ora file.

Troubleshooting Oracle Net Connection which is not working

Sometimes you setup a Oracle Net connection and it does not work. This is more likely to happen when you edit your tnsnames.ora file manually instead of using (NETCA) Oracle Net Configuration Assistant. This is because Oracle Net Configuration Assistant
  1. tests the connection capability when you create it and
  2. using Oracle Net Configuration Assistant reduces your chance of making a mistake.

If you are faced with a Oracle Net connection that is not working, there are several things that you should check:
  1. Whether your listener.ora file on the server is correct
  2. The syntax of your tnsnames.ora entry
  3. The underlying network connectivity
  4. The Oracle Net connectivity
  5. The default domain in your sqlnet.ora file

listener.ora File

The first item, the entry for the database in your listener.ora file, is normally an issue only when you have recently edited that file.

Oracle error TNS-03505: "Failed to resolve name"

The Oracle error TNS-03505: "Failed to resolve name" indicates an issue during the initial stages of establishing a connection to an Oracle database. It signifies that the TNS (Transparent Network Service) layer cannot locate the database you're trying to connect to.There are a few reasons why you might encounter this error:
  1. Missing or Incorrect TNS Entry: The most common cause is that the service name you're using to connect doesn't exist or is misspelled in the `tnsnames.ora` file. This file maps user-friendly service names to the actual connection details (host, port, SID) of the database. Double-check the service name you're using and ensure it matches an entry in your `tnsnames.ora`.
  2. Domain Name Issues (if applicable): If your `tnsnames.ora` uses a domain name to specify the host, make sure the domain name is spelled correctly and that your network can resolve it. Additionally, verify the `NAMES.DEFAULT_DOMAIN` parameter in your `sqlnet.ora` file (if present) is set correctly for your domain environment.
  3. Listener Not Running: The TNS layer communicates with a background process called the "listener service." Ensure the listener service is running on the database server you're trying to connect to. You can check its status using the `lsnrctl status` command on the server.
  4. Incorrect Network Configuration: Less likely, but in rare cases, firewall restrictions or incorrect network configuration might prevent the TNS layer from reaching the listener service. Verify that network communication is allowed between your client machine and the database server.
Troubleshooting Steps:
  • Verify the service name in your connection string matches an entry in `tnsnames.ora`.
  • Check for typos in the hostname or domain name used in the `tnsnames.ora` entry.
  • Confirm the listener service is running on the database server.
  • If using domain names, ensure proper domain name resolution and `NAMES.DEFAULT_DOMAIN` setting (if applicable).

By following these steps and considering the potential causes, you should be able to resolve the TNS-03505 error and successfully connect to your Oracle database.

SEMrush Software