The Tool Desk
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The error message, failing stage, and connection path determine why an Oracle migration tool cannot connect. Start by recording the complete error and checking the host, port, connect identifier or service name, credentials, and account state. Then test the same connection independently where possible. A listener error, naming error, timeout, and login failure each point to a different next check; the title alone is not enough to identify one root cause.
Why won’t my Oracle migration tool connect?
Connection failures can arise at several different points: the migration client may not reach the database, Oracle Net may not resolve the requested database address or service, authentication may fail, or the migration product may lack a required driver, repository, or connection resource. Cloud deployments can add private-endpoint, routing, firewall, and access-policy requirements.
Before changing settings, capture the migration tool and version, source and target database products and versions, where each endpoint runs, the connection method, and the complete error text and code. Record whether the failure occurs during a test connection, source discovery, repository setup, or the migration itself. That stage helps separate a connection problem from a later migration prerequisite.
Check the connection details and database account first
Compare the values configured in the tool with the intended database endpoint. Check the hostname, TCP port, connect string or alias, database service name, username, and password. If the connection uses a wallet, confirm that the tool is using the intended wallet and connection configuration.
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- Verify that the hostname resolves to the intended database endpoint and that the port is the listener’s TCP port.
- Check whether the connection identifier is a full connect descriptor or an alias, and confirm that it points to the intended service.
- Confirm the account is valid, enabled, unlocked, and not using an expired password.
- Check that the account has the grants required for the operation being attempted; a successful network connection does not establish that the account has sufficient privileges.
When possible, try the same connection string and authentication details in another suitable Oracle client, such as SQLcl, from a network location with access to the database. If that client connects but the migration tool does not, the comparison narrows the investigation toward the tool’s connection configuration, driver, or workflow. It does not by itself prove which of those is at fault.
Use the Oracle error code to choose the next check
| Error | What it points to | Next check |
|---|---|---|
| ORA-12541, TNS:no listener | No listener is available at the host and port specified by the connection. | Verify the destination host, port, and connect string, then check whether the listener is running and listening at that address. Oracle describes the error as “Cannot connect. No listener at host_port.” |
| ORA-12154 | The supplied connect identifier could not be resolved. | Check the alias and naming configuration. If the connection uses a TNS alias, verify that the intended tnsnames.ora file is being used and that the alias is present and correct. |
| ORA-12170 or another connection timeout | The client did not complete the connection within the expected time; this can involve reachability, routing, security rules, or listener responsiveness. | Check whether the client can reach the database host and port along the permitted network path, and whether security controls or a slow/unresponsive listener are blocking or delaying the connection. |
| ORA-12514 | The listener does not know the requested service. | Compare the requested service name with the services registered with the listener. Confirm that the connection targets the intended database or pluggable database (PDB). |
These errors identify different layers, not a universal fix. Oracle’s Oracle Net troubleshooting guidance covers these error classes; the precise check depends on the database version and how the connection is configured.
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Check the listener and service registration
For ORA-12541, confirm that a listener is running on the database host and listening on the host and port in the connection descriptor. A listener running on a different interface or port will not satisfy a client that is pointed elsewhere. Use the listener tools and administrative access appropriate to the database environment, or ask the database administrator to verify listener status and address.
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For ORA-12514, the listener may be reachable even though it does not recognize the requested service. Verify the exact service name and whether it is registered with the listener. If the migration is meant to connect to a PDB, make sure the descriptor names that PDB’s service rather than an unintended container or service.
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Trace the network path without opening access broadly
If the error is a timeout or unreachable-host failure, verify that the database is running and accepts TCP connections, then trace the route from the migration client to the database endpoint. Check subnet and route configuration, firewalls, security lists or network security groups, and any private endpoint or public-IP access controls that apply to the actual deployment.
- For a database in a cloud virtual network, confirm that the client and database have a permitted route and that the relevant security rules allow the database TCP port.
- For a private database endpoint, verify the endpoint setup and that the client is on a network that can reach it.
- For a shared Autonomous Database reached through a public IP with an access-control list, verify that the client’s address or CIDR range is allowed.
- For a customer-managed database, check host firewall rules and the database’s listener port.
- If a connection previously worked, check for a stopped database or service and for changes to network configuration, IAM or group membership, or database privileges.
Do not expose a database port to the public internet as a generic troubleshooting step. Use only the route and access controls intended for that deployment, and involve the network or database administrator if you do not manage them.
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Check the migration product only after identifying it
“Oracle migration tool” can refer to products with different connection models. A prerequisite for one product is not automatically relevant to another.
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Oracle SQL Developer Migrations
SQL Developer Migrations uses a migration repository and may need a configured JDBC driver for certain third-party source connections. If the failure occurs while setting up the repository, check the repository schema’s required privileges, including RESOURCE, CREATE SESSION, and CREATE VIEW. A repository privilege error is not evidence of a network failure; use the failing stage and reported error to distinguish them.
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Database Migration Assistant for Unicode (DMU)
DMU’s target connection details include an administrative username and password, hostname, TNS listener port, and database service name. Check that each matches the intended target. DMU’s supported database and operating-system configurations depend on the release in use; consult documentation for that release rather than treating an older getting-started page as a current compatibility matrix.
OCI Database Migration
OCI Database Migration represents source and target databases as connection resources. In a workflow using an Oracle PDB as the source, the PDB connection is required, and the CDB details may also be needed; Oracle notes that the CDB connection is not required for an offline migration. Confirm that the connection resources point to the intended databases and that the service has the required network access.
Transfer methods also have different constraints. A database link uses a direct SQL*Net connection. Oracle recommends Data Pump through a database link only for small databases because parallelism cannot be enabled with that method. These are OCI Database Migration workflow details, not general requirements for SQL Developer Migrations or DMU.
What to include when escalating the failure
If the checks do not isolate the issue, provide the database or network administrator—and, where relevant, the migration-tool support team—with enough detail to reproduce the connection path without sharing secrets:
Quick Recap
- Migration product and version, source and target database products and versions, and the stage that fails.
- The complete Oracle error code and message, with passwords and other secrets removed.
- Whether the connection uses a service name, TNS alias, wallet, private endpoint, database link, or another method.
- The client and database network locations, such as on-premises, a cloud subnet, or a bastion host, plus the intended host and port.
- Whether another Oracle client can connect from the same network location using the same endpoint and account.
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