ORA-12170: TNS:Connect timeout occurred

The client tried to reach the database and got no answer in time. Usually a firewall silently drops the packets, or the host or port is wrong. Test whether the port is reachable from the client’s own machine.

What ORA-12170 means

Unlike ORA-12541, where the server actively refuses the connection, here nothing answers at all. A silent drop is typical of firewalls and of VPN routes that do not reach the server. ORA-12170 can also mean the server was too busy to accept the connection in time.

Common causes of ORA-12170

A firewall between client and server blocking port 1521.
A wrong host name or IP address, or the VPN not being connected.
A server that is down or unreachable on the network.
A busy server or listener not answering within the timeout.

How to fix ORA-12170

Test the port from the client: nc -vz host 1521, or Test-NetConnection on Windows.
Check that the name resolves to the right address.
Check the VPN and firewall rules, on the server host too.
If the network is fine, see whether the server is overloaded and check the listener log.

ORA-12170 example

Is the port reachable?

# macOS / Linux
nc -vz db-host.example.com 1521

# Windows PowerShell
Test-NetConnection db-host.example.com -Port 1521

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Oracle documentation for ORA-12170. Oracle is a registered trademark of Oracle Corporation. SQLlightspeed is not affiliated with Oracle.