Remote Oracle Net connections hang -Doc ID 1302367.1

Symptoms:  Something may occur where there is a connectivity problem between clients or servers and a remote database such as standby or DR site.  What happens with a SQLPLUS test hang.  For example:  sqlplus username/password@remote_sid--> hangs

Cause determination:  One potential cause of this condition, is that a TCP/IP network device (firewall, router, etc.) located between the client and server is set to restrict or limit communication through it when nay MTU or packet size is exceeded.  This is an MTU setting at the network level, so the systems or network admin needs to analyze and correct the MTU setting.  The MTU setting problem is typical issue that caused the sqlplus in the remote site/standby site hang.

To enable traces for the hanging sqplus session:

sqlnet.ora, you need to add
DIAG_ADR_ENABLED=OFF
TRACE_LEVEL_CLIENT=16
TRACE-DIECTORY_CLIENT= <location> is the directory to write trace file to

Solution:  Verify the MTU settings from the network devices.