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How to Resolve ORA-12535: TNS:operation timed out

ORA-12535 and TNS-12535

ORA-12535 is the same as TNS-12535, they all indicate that the connection between the client and the listener has been timed out.

First, let’s see how we reproduce TNS-12535.

C:\Users\ed>tnsping compdb

TNS Ping Utility for 64-bit Windows: Version - Production on 22-JUL-2014 19:03:21

Copyright (c) 1997, 2013, Oracle.  All rights reserved.

Used parameter files:

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = primary01)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = compdb)))
TNS-12535: TNS:operation timed out


TNS-12535 means the connect identifier can be found in tnsnames.ora and the hostname is resolvable by DNS or /etc/hosts, but somehow network problems make the connection timed out.

There could be several causes of TNS-12535 that I listed below.

  1. The hostname in the connect descriptor of compdb points to a wrong IP address.
  2. The port specified in the connect descriptor of compdb points to a wrong one.
  3. The port specified in the connect descriptor of compdb is not opened on firewall of the database server.
  4. DNS or /etc/hosts points to a wrong IP address while resolving domain name.
  5. Any other anti-virus software on clients.
  6. The server has been shutdown, there's no way to go.


  1. Inspect the content of tnsnames.ora closely once again to make sure there's no any typo or mistake.
  2. Check your DNS, /etc/hosts or C:\Windows\System32\drivers\etc\hosts file to make sure the IP mapping is correct. Additionally, make sure the format of IP mapping is correct.
  3. Open the port 1521.
  4. Revert any changes of security policy on network appliances including IPS, IDS and firewall. I have ever met a case related to IPS.
  5. If the server is down, then recover server's availability.
  6. Usually, TNS-12535 accompanies with ORA-3136 (or ORA-03136), you may consider to raise timeout period on the server.

For more connection troubleshooting, you may refer to Oracle 19c Net Services Administrator's Guide: 15 Testing Connections.

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