When I set the connecting information on the GUI in SQLDeveloper I get the following error (everytime!)

Status : Failure -Test failed: IO Error: The Network Adapter could not establish the connection

Connection information:

user: hr

pass: hr

Conn. type: basic / Role: default

hostname: localhost

port: 1521

SID: xe

I couldn't connect with the sys user either.

Previously I successfully unlocked the HR user through SQLPLUS command line

(as described here:

and set the port=localhost in the tnsnames.ora and listener.ora, the OracleXETNSListener service is up and running as well as the OracleServiceXE)

Sadly I'm still getting this error message...

I'm on a laptop (with wireless wifi connection only), under Windows 7. What might be the problem? Thank you for your help.

1 Answer 1


In the meantime I figured it out myself.

The connection couldn't be established from SQL Developer because I was logged into my company's VPN and so "localhost" was resolved somehow as an IPV6 address.

When I closed the VPN connection and tried to connect with the same connection information it worked, localhost was resolved as normal IPV4 address then.

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