Below is based upon excellent comment from Ask Tom
Database connection closed on port
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General
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Application recieve time out errors.
When checking Oracle alert.log, there are following messages
Step 1. - check alert.log
less alert.log
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Archived Log entry 160083 added for thread 1 sequence 160094 ID 0x36162634 dest 1:
Wed Sep 06 05:12:16 2017
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Fatal NI connect error 12170.
VERSION INFORMATION:
TNS for Linux: Version 11.1.0.7.0 - Production
Oracle Bequeath NT Protocol Adapter for Linux: Version 11.1.0.7.0 - Production
TCP/IP NT Protocol Adapter for Linux: Version 11.1.0.7.0 - Production
Time: 06-SEP-2017 05:12:16
Tracing not turned on.
Tns error struct:
ns main err code: 12535
TNS-12535: TNS:operation timed out
ns secondary err code: 12560
nt main err code: 505
TNS-00505: Operation timed out
nt secondary err code: 110
nt OS err code: 0
Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=111.222.555.200)(PORT=43680))
Wed Sep 06 05:32:39 2017
Thread 1 advanced to log sequence 160096 (LGWR switch)
Step 2. - get listener log details
Search for server 111.222.555.200 in listener logs
oracle@my_server:/software/oracle/diag/rdbms/igt/igt/trace>% lsnrctl status LSNR_IGT
LSNRCTL for Linux: Version 11.1.0.7.0 - Production on 06-SEP-2017 06:34:43
Copyright (c) 1991, 2008, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=ora_server)(PORT=1521)))
STATUS of the LISTENER
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Alias lsnr_igt
Version TNSLSNR for Linux: Version 11.1.0.7.0 - Production
Start Date 18-JUL-2016 10:52:34
Uptime 414 days 19 hr. 42 min. 8 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /software/oracle/111/network/admin/listener.ora
Listener Log File /software/oracle/diag/tnslsnr/my_server/lsnr_igt/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=100.000.555.125)(PORT=1521)))
Services Summary...
Service "igt" has 1 instance(s).
Instance "igt", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully
Step 3. - in listener log, look to IP 10.128.156.200:
less /software/oracle/diag/tnslsnr/my_server/lsnr_igt/alert/log.xml
<msg time='2017-09-06T04:16:39.191+00:00' org_id='oracle' comp_id='tnslsnr'
type='UNKNOWN' level='16' host_id='my_server'
host_addr='10.0.156.126'>
<txt>06-SEP-2017 04:16:39 * (CONNECT_DATA=(SID=igt)(CID=(PROGRAM=)(HOST=__jdbc__)(USER=iu))) * (ADDRESS=(PROTOCOL=tcp)(HOST=111.222.555.200)(PORT=45413)) * establish * igt * 0
</txt>
</msg>
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Additional info, per "Ask Tom" post:
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Basically it means that there is a network issue between client and the server.
It could be client itself, or a firewall timeout, or a timeout on some network hardware between the two devices.
These time out related messages are mostly informational in nature.
The messages indicate the specified client connection (identified by the 'Client address:' details) has experienced a time out.
The 'nt secondary err code' identifies the underlying network transport, such as (TCP/IP) timeout limits after a client has abnormally terminated the database connection.
The 'nt secondary err code' translates to underlying network transport timeouts for the following Operating Systems:
For the Solaris system: nt secondary err code: 145:
ETIMEDOUT 145 /* Connection timed out */
For the Linux operating system: nt secondary err code: 110
ETIMEDOUT 110 Connection timed out
For the HP-UX system: nt secondary err code: 238:
ETIMEDOUT 238 /* Connection timed out */
For AIX: nt secondary err code: 78:
